variant-analysis

Overview of variant-analysis skill

variant-analysis is a security-focused skill for finding related bugs after you already have one confirmed issue. It helps you turn a single vulnerable pattern into a repeatable search across a codebase, which is especially useful for Security Audit work, exploit triage, and building better CodeQL or Semgrep rules.

What variant-analysis is best for

Use the variant-analysis skill when you need to answer: “Where else does this same root cause appear?” It fits post-discovery audits, not broad exploratory review. The real job-to-be-done is to map one confirmed weakness into a search pattern, then test that pattern against similar code paths.

What makes it different

The variant-analysis guide is opinionated about root cause first, pattern second. It emphasizes exact matches before abstraction, then gradually widens the search until you balance recall and false positives. That makes it more reliable than a generic “find similar code” prompt, especially when you need defensible findings.

When it will pay off

This skill is most valuable when bugs cluster through copy-paste, framework misuse, incomplete fixes, or repeated dangerous API use. If you already know the sink, source, and missing protection, variant-analysis can help you find variants much faster than manual grep alone.

How to Use variant-analysis skill

Install and open the right files

For variant-analysis install, use the directory’s skill install flow for trailofbits/skills, then start with SKILL.md and METHODOLOGY.md. After that, inspect resources/variant-report-template.md and the language-specific rules in resources/codeql/ and resources/semgrep/ to see how the skill expresses findings in practice.

Give the skill a root-cause statement

The best variant-analysis usage starts with a precise vulnerability statement, not a vague goal. Strong input looks like: “Untrusted HTTP parameter reaches exec() without argument separation” or “User-controlled path reaches file open without canonicalization.” That single sentence becomes the search pattern.

Follow the exact-to-abstract workflow

Start with an exact match for the original bug, then generalize only if the first pass is too narrow. A good workflow is: identify the dangerous operation, confirm the missing guard, search for identical code shape, then broaden to equivalent APIs or framework idioms. This is the core variant-analysis usage pattern because it reduces false positives early.

Use the supplied resources as templates

The repository’s resources/codeql/*.ql and resources/semgrep/*.yaml files are practical references for how to encode variants by language. Read the file for your stack first, then adapt sources, sinks, and sanitizers to your project’s framework conventions. For Security Audit work, the report template is especially useful because it forces you to record root cause, location, and false-positive reasoning.

variant-analysis skill FAQ

Is variant-analysis for finding new bugs from scratch?

No. It is not the best fit for initial discovery. The variant-analysis skill assumes you already know the bug pattern and want to search for siblings, not start from zero.

How does it compare with a normal prompt?

A normal prompt can suggest generic checks, but variant-analysis gives you a disciplined sequence: understand the original issue, make an exact match, then widen the search. That structure matters when you need reproducible Security Audit results instead of a one-off hunch.

Is it beginner-friendly?

Yes, if you can describe the original vulnerability in plain language. You do not need to write perfect CodeQL or Semgrep on day one, but you do need a concrete source, sink, and missing protection. Without that, the search will be too broad to trust.

When should I not use it?

Do not use variant-analysis for general code review, unfamiliar-code orientation, or writing remediation text. If you only want to understand a repository, or only need a fix recommendation, another workflow will give better results.

How to Improve variant-analysis skill

Be specific about the exploit path

The biggest quality lever is input precision. Instead of “look for command injection,” say exactly how data flows, which API is dangerous, and what safeguard is missing. The variant-analysis skill performs best when you define the root cause in a way a rule can test.

Tell it what safe code looks like

False positives drop when you describe the expected guardrails. For example: “flag subprocess.run() only when user input reaches a shell command string,” or “ignore paths that pass through filepath.Clean() and a base-directory check.” This helps the variant-analysis guide separate true variants from intended behavior.

Iterate from findings, not theory

After the first pass, compare results against the template in resources/variant-report-template.md and refine the search pattern based on what was noisy or missed. If you find only trivial matches, widen the abstraction level; if you get too many false positives, narrow the source set or add sanitizers. That feedback loop is what makes variant-analysis for Security Audit practical.

Adapt per language and framework

Use the language-specific CodeQL or Semgrep examples as starting points, not universal rules. The best variant-analysis improvement is to swap in your project’s real sources, sinks, and safe wrappers so the search matches how your code actually behaves.