ctf-rev

ctf-rev is a skill for Claude Code from 26zl/cybersec-toolkit. It costs 86 tokens per session (1,048 once invoked), scanned A, original, MIT.

A workflow for reverse-engineering compiled programs in capture-the-flag (CTF) competitions. It covers identifying binaries, unpacking them, and studying native, .NET, Java, Android, and web-assembly files.

In plain words
What is it for?
Use it to inspect strings and file protections, detect packers, choose a decompiler, recover useful symbols, and analyze binaries across several platforms.
Why use it?
It gives you an ordered way to understand a program when source code is missing, symbols were removed, or the file is deliberately packed or obfuscated.

Skill for Claude Code

Written for Claude Code: installed under .claude/.

Part of the cybersec-toolkit plugin — 197 skills, 2 hooks, 1 MCP server shipped together

Good fit Use it to inspect strings and file protections, detect packers, choose a decompiler, recover useful symbols, and analyze binaries across several platforms.

Compare 6 skills from other repositories ↓
Install with agentmods
npx agentmods add skills/26zl/cybersec-toolkit/ctf-rev
Install

Getting it into your agent

One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.

Any agent
npx skills add 26zl/cybersec-toolkit --skill ctf-rev
Clone the repo
git clone --depth 1 https://github.com/26zl/cybersec-toolkit

Made for: Claude Code.

Or install cybersec-toolkit, the plugin that ships this one along with the rest of its 197 skills, 2 hooks, 1 MCP server.

Wrote this? Show the measurements

A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.

agentmods badge for ctf-rev

README.md
[![agentmods](https://agentmods.dev/badge/skills/26zl/cybersec-toolkit/ctf-rev.svg)](https://agentmods.dev/skills/26zl/cybersec-toolkit/ctf-rev)
Your own site
<a href="https://agentmods.dev/skills/26zl/cybersec-toolkit/ctf-rev"><img src="https://agentmods.dev/badge/skills/26zl/cybersec-toolkit/ctf-rev.svg" alt="Measured on agentmods" height="20"></a>
Per session 86 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 1,048 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. A grade says what 26 rules found in the file — not that it is safe. Third-party audits
  • NVIDIA SkillSpector pass 7 Sept 2026
How audits are shown
Origin original No closer match found in the catalogue.
Token cost

What it costs to keep this loaded

Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.

ModelPer sessionOnce invoked
Fable 5.1 $0.00086 $0.01048
Opus 5 $0.00043 $0.00524
Sonnet 5 $0.00017 $0.00210
Haiku 4.5 $0.00009 $0.00105

Measured 4d ago against content hash bcb303573b9b, method: parsed. Prices are Anthropic first-party input rates as of 2026-09-08, from the pricing page.

Security

Grade A, and why

ctf-rev scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 4d ago.

A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.

Nothing flagged

None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.

.claude/skills/ctf-rev/SKILL.md · 109 lines

How it starts

The opening of the file, as written. The whole thing — 109 lines — stays where its author put it; the contents beside it link to each section on GitHub.

CTF reverse engineering methodology

1. Triage

file ./bin
strings ./bin | head -50
strings ./bin | grep -i "flag\|ctf{\|password\|key"
xxd ./bin | head -20                       # magic bytes
checksec --file=./bin                      # protections

2. Detect packing

# Entropy check (>7.5 = packed/encrypted)
ent ./bin   # or: python3 -c "from collections import Counter; ..."

# UPX / known packers
upx -t ./bin            # tests + identifies UPX
detect-it-easy-cli ./bin
diec ./bin

If UPX-packed: upx -d ./bin -o unpacked. For custom packers: dump from memory after unpacking stub runs (gdb / x64dbg).

3. Pick the decompiler

Binary type Best tool
ELF / PE / Mach-O Ghidra (registry), IDA (commercial), Binary Ninja
Stripped ELF Ghidra + recover symbols via FunctionID / Lumen
.NET (DLL/EXE) dnSpyEx, ilspycmd, dotPeek
Java JAR jadx, cfr, procyon
Java class javap -c -p
Android APK jadx-gui, apktool d then jadx on dex
iOS / Mach-O Hopper, Ghidra
Go binary redress, GoReSym, Ghidra + Go plugin
Rust Ghidra + rustfilt for symbols
WASM wabt (wasm-decompile), wasmer for run
Python .pyc uncompyle6, decompyle3, pycdc
PyInstaller .exe pyinstxtractor then pycdc on .pyc
Compiled Lua unluac, luadec

4. Dynamic analysis

# Trace
ltrace ./bin
strace ./bin
strace -f -e trace=read,write,open ./bin

# Debugger
gdb-multiarch ./bin
# pwndbg or gef extensions are loaded by default

# Fault injection / branch flipping
gdb> set $eax = 1     # change return value to bypass check

For Android: frida for runtime instrumentation, objection on top.

5. Anti-debug / anti-VM

Common checks:

  • ptrace(PTRACE_TRACEME) returns -1 if already debugged → patch with nop
  • /proc/self/status TracerPid: 0 check → LD_PRELOAD a fake or patch
  • timing checks (rdtsc) → patch
  • IsDebuggerPresent() (Windows) → patch the call site

Read the full file on GitHub · 109 lines

Changes

What this file has done since we first saw it

Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.

  1. 4d ago First seen · 109 lines · 86 tokens per session scan A bcb303573b9b

Subscribe to this mod's changes

ctf-rev is a skill published in the GitHub repository 26zl/cybersec-toolkit (49 stars, last pushed today), licensed MIT. It adds 86 tokens to every session and 1,048 once invoked, about $0.0004 per session on Opus 5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-09-03.

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