Malware Analysis

Malware Analysis is a skill for Claude Code, Codex from buzzer-re/Rikugan. It costs 21 tokens per session (1,175 once invoked), scanned A, original, MIT.

A workflow for examining potentially malicious Windows PE files, the executable format used by Windows programs. It covers obfuscation, code, strings, imports, network and cryptographic indicators, and MITRE ATT&CK mapping.

In plain words
What is it for?
Use it to inspect malware behavior, find encrypted strings and cryptographic code, extract indicators of compromise, and map findings to the MITRE ATT&CK framework.
Why use it?
It gives analysts a structured way to understand suspicious binaries and record signs of compromise without exposing indicator links.

Skill for Claude CodeCodex

Written for no agent in particular: nothing here depends on one.

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.

agentmods
npx agentmods add skills/buzzer-re/rikugan/malware-analysis
Any agent
npx skills add buzzer-re/Rikugan --skill malware-analysis
Clone the repo
git clone --depth 1 https://github.com/buzzer-re/Rikugan

Made for: Claude Code, Codex.

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 Malware Analysis

README.md
[![agentmods](https://agentmods.dev/badge/skills/buzzer-re/rikugan/malware-analysis.svg)](https://agentmods.dev/skills/buzzer-re/rikugan/malware-analysis)
Your own site
<a href="https://agentmods.dev/skills/buzzer-re/rikugan/malware-analysis"><img src="https://agentmods.dev/badge/skills/buzzer-re/rikugan/malware-analysis.svg" alt="Measured on agentmods" height="20"></a>
Per session 21 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 1,175 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. Scan, not verified.
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 $0.00021 $0.01175
Opus 5 $0.00010 $0.00588
Sonnet 5 $0.00004 $0.00235
Haiku 4.5 $0.00002 $0.00118

Measured 6d ago against content hash a432a6d60013, method: parsed. Prices are Anthropic first-party input rates as of 2026-09-06, from the pricing page.

Security

Grade A, and why

Malware Analysis 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 6d 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.

rikugan/skills/builtins/malware-analysis/SKILL.md · 102 lines

How it starts

The opening of the file, as written. The whole thing — 102 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Task: Malware Analysis. You are analyzing a potentially malicious Windows PE binary. Defang all IOCs (hxxps://, [.]).

Phase 0: Obfuscation Triage

Before analysis, check for obfuscation:

  1. Decompile the entry point and a few key functions
  2. If code is heavily obfuscated (opaque predicates, CFF, MBA): invoke /deobfuscation first
  3. If very few readable strings in a large binary → strings are encrypted
  4. Look for the string decode stub: a small function called before every string use
  5. If strings are encrypted: trace the decode function, understand the algorithm (XOR, RC4, custom)

Crypto constant hunting: When you find RC4 S-box or AES constants via search_strings, use xrefs_to on the constant's address (not the S-box itself) → finds KSA/key schedule → decompile that → xrefs_to on it → finds the encrypt/decrypt wrapper. Do NOT use hex pattern search for KSA byte-swap — too many false positives.

Phase 1: Reconnaissance

Use built-in tools for initial survey:

  1. get_binary_info — format, architecture, size, function count
  2. list_imports — group by DLL, identify capabilities:
    • WINHTTP/WININET = Network communication
    • CRYPT32/ADVAPI32 (Crypt*) = Cryptographic operations
    • GDI32 = Screenshot capture
    • ntdll = Low-level ops, possible direct syscalls
  3. list_strings + search_strings — look for URLs, API paths, user agents, mutex names, file extensions, registry paths, app paths (Discord, Telegram, Chrome)
  4. list_exports — exported functions and ordinals

Batch these calls: get_binary_info + list_imports + list_exports can run in parallel.

Phase 2: Execution Flow

  1. Decompile entry point / WinMain with decompile_function
  2. Identify the execution sequence and lifecycle: init → config → steal → exfil → exit
  3. Use function_xrefs to map the call graph from entry
  4. Categorize functions: initialization, C2, stealing modules, exfiltration, cleanup

Phase 3: Targeted Analysis — Kill Chain

For network malware:

  • Trace: socket init → DNS resolution → connect → send/recv
  • Identify C2 protocol (raw socket, HTTP, DNS tunneling)
  • Extract C2 config (hardcoded IP/domain or decrypted)

Read the full file on GitHub · 102 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. 6d ago First seen · 102 lines · 21 tokens per session scan A a432a6d60013

Subscribe to this mod's changes

Malware Analysis is a skill published in the GitHub repository buzzer-re/Rikugan (672 stars, last pushed 2mo ago), licensed MIT. It adds 21 tokens to every session and 1,175 once invoked, about $0.0001 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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