scanning-samples-with-yara

scanning-samples-with-yara is a skill for Claude Code, Codex from meltedinhex/analyst-ai-pack. It costs 65 tokens per session (765 once invoked), scanned A, original, Apache-2.0.

A guide to using YARA, a rule-based file scanner, to classify suspicious files by their strings and byte patterns.

In plain words
What is it for?
Use it to organise and apply YARA rules, inspect matched strings and file locations, tune false positives, and triage directories of samples.
Why use it?
It speeds up the first pass over many samples and helps test whether files resemble a malware family or capability. A match alone does not prove where a sample came from.

Skill for Claude CodeCodex

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

Good fit Use it to organise and apply YARA rules, inspect matched strings and file locations, tune false positives, and triage directories of samples.

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Install with agentmods
npx agentmods add skills/meltedinhex/analyst-ai-pack/scanning-samples-with-yara
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 meltedinhex/analyst-ai-pack --skill scanning-samples-with-yara
Clone the repo
git clone --depth 1 https://github.com/meltedinhex/analyst-ai-pack

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.

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README.md
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Your own site · 80×15
<a href="https://agentmods.dev/skills/meltedinhex/analyst-ai-pack/scanning-samples-with-yara"><img src="https://agentmods.dev/badge/skills/meltedinhex/analyst-ai-pack/scanning-samples-with-yara.svg" alt="Reviewed on agentmods" width="80" height="20"></a>
Per session 65 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 765 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.
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 $0.00065 $0.00765
Opus 5 $0.00032 $0.00382
Sonnet 5 $0.00013 $0.00153
Haiku 4.5 $0.00006 $0.00076

Measured 9d ago against content hash 132919157361, method: parsed. Prices are Anthropic first-party input rates as of 2026-09-12, from the pricing page.

Security

Grade A, and why

scanning-samples-with-yara 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 9d ago.

The scan reads SKILL.md. This mod also ships 1 executable file (scripts/analyst.py), listed below but not scanned — reading those needs a real analyzer, not pattern matching.

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.

skills/scanning-samples-with-yara/SKILL.md · 100 lines

How it starts

The opening of the file, as written. The whole thing — 100 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Scanning Samples with YARA

When to Use

  • You want to classify one or many samples against known malware-family or capability rules.
  • You need to confirm a family hypothesis with a targeted rule and read which strings matched.
  • You are triaging a directory of files and want to flag the suspicious ones.

Do not use a YARA match as proof of family attribution on its own — public rules vary in quality and can over-match. Corroborate with behavior or code analysis.

Prerequisites

  • yara CLI or yara-python (pip install yara-python).
  • A curated rule set (your own plus vetted public rules). Avoid blindly merging large noisy collections.
  • Samples in neutralized form inside the lab.

Workflow

Step 1: Organize rules

Keep rules in categories (family, capability, packer, anomaly) and compile them once for speed. Tag rules so matches are self-describing.

Step 2: Scan and read matches

python scripts/analyst.py scan rules/ sample.bin
# prints matched rule names, tags, and matched strings with offsets

The matched string offsets matter: they tell you where in the file the signal is (header, overlay, resource), which guides deeper analysis.

Step 3: Triage a directory

python scripts/analyst.py scan rules/ ./samples --recursive --summary

Rank files by number/severity of matches to prioritize analyst time.

Step 4: Tune for false positives

If a rule fires on benign files, tighten it: require multiple strings (2 of ($a*)), anchor to file structure (uint16(0) == 0x5A4D), or raise the condition specificity.

Step 5: Promote good signals to detection

A rule that reliably identifies a family or capability becomes a hunting/detection artifact — hand it to the detection-engineering workflow.

Validation

  • Matches reproduce across runs and tools (CLI and yara-python agree).
  • Each kept rule has an acceptable false-positive rate against a known-clean corpus.
  • Match offsets correspond to meaningful file regions, not incidental byte coincidences.

Read the full file on GitHub · 100 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. 9d ago First seen · 100 lines · 65 tokens per session scan A 132919157361

Subscribe to this mod's changes

scanning-samples-with-yara is a skill published in the GitHub repository meltedinhex/analyst-ai-pack (22 stars, last pushed 2mo ago), licensed Apache-2.0. It adds 65 tokens to every session and 765 once invoked, about $0.0003 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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