ctf-malware

ctf-malware is a skill for Claude Code from ljagiello/ctf-skills. It costs 101 tokens per session (2,197 once invoked), scanned A, original, MIT.

A reference guide for analysing malicious software and network traffic in capture-the-flag (CTF) security puzzles. It covers scripts, binaries, encrypted communications, memory evidence, and methods malware uses to hide its behaviour.

In plain words
What is it for?
Deobfuscating scripts, examining Windows and .NET programs, analysing command-and-control traffic, decoding custom encryption, inspecting memory, and writing detection rules.
Why use it?
It gives investigators a structured way to understand suspicious code, uncover its communication protocol, and detect obfuscation or evasion techniques.

Skill for Claude Code

Written for Claude Code: allowed-tools in frontmatter. Also seen: mentions Claude Code.

Good fit Deobfuscating scripts, examining Windows and .NET programs, analysing command-and-control traffic, decoding custom encryption, inspecting memory, and writing detection rules.

Compare 6 skills from other repositories ↓
Install with agentmods
npx agentmods add skills/ljagiello/ctf-skills/ctf-malware
About the project

ctf-skills is a collection of agent instructions for solving capture-the-flag security challenges, including web exploitation, binary vulnerabilities, cryptography, reverse engineering, forensics, and OSINT. It is intended for agents and people working through CTF problems, and its skills can be loaded into supported coding-agent workflows.

ljagiello/ctf-skills · 3,234 stars · on GitHub · ljagiello.github.io

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 ljagiello/ctf-skills --skill ctf-malware
Clone the repo
git clone --depth 1 https://github.com/ljagiello/ctf-skills

Made for: Claude Code.

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-malware

README.md
[![agentmods](https://agentmods.dev/badge/skills/ljagiello/ctf-skills/ctf-malware/github.svg)](https://agentmods.dev/skills/ljagiello/ctf-skills/ctf-malware)
Your own site
<a href="https://agentmods.dev/skills/ljagiello/ctf-skills/ctf-malware"><img src="https://agentmods.dev/badge/skills/ljagiello/ctf-skills/ctf-malware/github.svg" alt="Measured on agentmods" height="20"></a>

Or the 80×15 button, for a site that already has a row of RSS and ATOM ones. Only the verdict fits; the numbers stay here.

agentmods 80×15 button for ctf-malware

Your own site · 80×15
<a href="https://agentmods.dev/skills/ljagiello/ctf-skills/ctf-malware"><img src="https://agentmods.dev/badge/skills/ljagiello/ctf-skills/ctf-malware.svg" alt="Reviewed on agentmods" width="80" height="20"></a>
Per session 101 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 2,197 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
  • Socket pass 18 Apr 2026
  • Snyk fail 18 Apr 2026
  • NVIDIA SkillSpector warn 7 Sept 2026
SkillSpector: 1 finding, up to critical

These are SkillSpector’s own severities. On a checked sample its high-severity flags on skills were ~96% false positives — a documented command, a public API, a “never do X” rule — so we show them as a caution to read, not a verdict. Why →

  • critical YARA Match · line 20
    YARA rule matched a known malware signature (reverse shell, backdoor, ransomware, C2 framework, or info stealer).
    Fix: Remove the malware payload or compromised file entirely. Investigate how it entered the skill and audit all other artifacts for additional indicators of compromise.
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 $0.00101 $0.02197
Opus 5 $0.00051 $0.01099
Sonnet 5 $0.00020 $0.00439
Haiku 4.5 $0.00010 $0.00220

Measured 11d ago against content hash 3a73e3ea43b2, method: parsed. Prices are Anthropic first-party input rates as of 2026-09-10, from the pricing page.

Security

Grade A, and why

ctf-malware 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 11d 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.

Origin

Copies of this mod

3 near-identical copies found in the catalogue:

ctf-malware/SKILL.md · 180 lines

How it starts

The opening of the file, as written. The whole thing — 180 lines — stays where its author put it; the contents beside it link to each section on GitHub.

CTF Malware & Network Analysis

Quick reference for malware analysis CTF challenges. Each technique has a one-liner here; see supporting files for full details with code.

Prerequisites

Python packages (all platforms):

pip install yara-python pefile capstone oletools unicorn pycryptodome \
  volatility3 dissect.cobaltstrike

Linux (apt):

apt install strace ltrace tshark binwalk binutils

macOS (Homebrew):

brew install wireshark binwalk binutils ghidra

Manual install:

  • dnSpy — GitHub, .NET decompiler (Windows)

Additional Resources

  • scripts-and-obfuscation.md - JavaScript deobfuscation, PowerShell analysis, eval/base64 decoding, junk code detection, hex payloads, Debian package analysis, dynamic analysis techniques (strace/ltrace, network monitoring, memory string extraction, automated sandbox execution), YARA rules for malware detection, shellcode analysis (Unicorn Engine, Capstone), memory forensics for malware (Volatility 3 malfind, process injection detection), anti-analysis techniques (VM detection, timing evasion, API hashing, process injection), trojanized plugin analysis with custom alphabet C2 decoding
  • c2-and-protocols.md - C2 traffic patterns, custom crypto protocols, RC4 WebSocket, DNS-based C2, network indicators, PCAP analysis, AES-CBC, encryption ID, Telegram bot recovery, Poison Ivy RAT Camellia decryption
  • pe-and-dotnet.md - PE analysis (peframe, pe-sieve, pestudio), .NET analysis (dnSpy, AsmResolver), LimeRAT extraction, sandbox evasion, malware config extraction, PyInstaller+PyArmor

When to Pivot

  • If the sample is really just a normal crackme, packed challenge binary, or custom VM with no malware behavior, switch to /ctf-reverse.
  • If the main job is network reconstruction, disk carving, or host artifact recovery, switch to /ctf-forensics.
  • If the challenge turns into public attribution or infrastructure tracing, switch to /ctf-osint.

Read the full file on GitHub · 180 lines

Files

What ships with it

3 files beside SKILL.md in the same directory: the scripts, references and assets a skill reads on demand. Not counted in the per-session cost; read them before you install if any of them is executable.

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. 11d ago First seen · 180 lines · 101 tokens per session scan A 3a73e3ea43b2

Subscribe to this mod's changes

ctf-malware is a skill published in the GitHub repository ljagiello/ctf-skills (3,234 stars, last pushed 16d ago), licensed MIT. It adds 101 tokens to every session and 2,197 once invoked, about $0.0005 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 2026-08-30.

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