exploiting-format-string-vulnerabilities

Exploits format string bugs in printf-family functions to leak memory and hijack control flow.

954|172|Updated Mar 13, 2026

Search Tags:#memory leak #pwntools #CTF #printf #binary exploitation #format string #GOT overwrite

One-click install

npx skills add https://github.com/xalgord/xalgorix --skill exploiting-format-string-vulnerabilities

Or copy as Structured Prompt for Agent▼

Please help me install this Agent Skill.
Skill: exploiting-format-string-vulnerabilities
Source: https://github.com/xalgord/xalgorix/tree/main/internal/tools/skills/data/binary-exploitation/exploiting-format-string-vulnerabilities
Command: npx skills add https://github.com/xalgord/xalgorix --skill exploiting-format-string-vulnerabilities

SYSTEM DOCUMENTATION & REQUIREMENTS

💡 This Skill requires pwntools.

What problem does it solve?

During authorized binary exploitation assessments, format string vulnerabilities require precise offset discovery, careful payload byte ordering, and error-prone %n write arithmetic that often fails silently. This Skill provides a confirmed methodology for turning attacker-controlled format arguments into reliable memory-disclosure and arbitrary-write primitives.

Core Features & Use Cases

Offset Discovery and Read Primitives: Brute-force the stack argument offset with %N$p probes, then leak stack contents, libc pointers, and stack canaries to defeat ASLR, PIE, and canary protections.
Arbitrary Write via %n/%hn: Craft single or multi-half writes to overwrite GOT entries, .fini_array destructors, or saved return addresses, using pwntools fmtstr_payload and FmtStr to automate the math.
Use Case: Given a 32-bit no-RELRO binary calling printf(user_input) in a loop, confirm the input offset, leak the libc base, overwrite printf@GOT with system, and send /bin/sh on the next pass to obtain a shell.

Quick Start

Analyze the target binary ./chall for a format string vulnerability, confirm the argument offset, and build a pwntools exploit that leaks libc and overwrites the GOT to spawn a shell.

Frequently Asked Questions about exploiting-format-string-vulnerabilities

High-intent search queries and answers about installing and using this skill.

FAQPage Schema

How do I exploit a format string vulnerability with pwntools?▼

Use fmtstr_payload(offset, {target_address: value}) to automatically craft the multi-write payload, or the FmtStr class with execute_fmt for interactive targets. pwntools computes the offset and splits writes into %hn operations, avoiding manual HOB/LOB arithmetic errors.

How are format string bugs exploited on Windows x64?▼

When a buggy _snprintf call passes no varargs, conversions read pointers from the RCX, RDX, R8, and R9 registers. A leading %p leaks a stable in-module pointer from R9, letting you recover the image base and build a ROP chain.