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cors-auditor

Skill13 starsChanged 5 months agoMITView on GitHub

Audit a site's Cross-Origin Resource Sharing (CORS) configuration for misconfigurations — wildcard origin with credentials, reflected arbitrary Origin, the 'null' origin, overly broad allowed methods, and risky credentialed CORS. Use when the user asks to "check my CORS config", "is my API's CORS safe", "test for CORS misconfiguration", or "why can any site call my API".

1 other project uses a version of this.

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    1. Starr-del/ShipSafe★ 0same name

    How matches are found. Word for word: the exact same text. Edited: shares passages with this file (“99% same” means 99% of its five-word phrases also appear here; 10% or more counts). Their own version: similar meaning, or, weakest, the same name. We can’t tell which project had it first. Projects are counted among the 200 most-starred candidates, and mentions are links to the repository we found, up to 50 per site, so both counts are a floor.

  • In this repository7 other files it gives its agents.

The file

We split this skill into the rules it gives an agent

2 rules. About 0 are common, 1 is distinctive, and 1 is very specific to this project.

  • ≈0

    Common · estimate

    Many files like this have a rule of this kind.

  • ≈1

    Distinctive · estimate

    This author's own choices. Worth a look.

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  • Common
  • Distinctive
  • Very specific
  1. Very specific:

    Every reported finding fails the build.

    line 55
  2. Distinctive:

    Only test APIs the user owns or is authorized to test.

    line 67

≈ “Common” is an estimate: at least 1 in 5 of the 350,495 skill files we read have a rule of the same kind, not the same words. “Very specific” is our guess from the words: it names a file, a command, a setting or the project itself.

Keep what fits and drop the rest. Your version, ready for your agents.
Files
SKILL.md

CORS Misconfiguration Auditor

Inspects CORS response headers and reports exploitable misconfigurations with fixes. The analysis core is pure and offline-testable; live probing uses only stdlib urllib and sends a throwaway Origin header to detect origin reflection.

When to use this skill

  • "Audit the CORS configuration of https://api.example.com."
  • "Is it safe that my API returns Access-Control-Allow-Origin: *?"
  • "Does my server reflect any Origin back?"

What it checks

  • Wildcard + credentials — Allow-Origin: * with Allow-Credentials: true (cors-wildcard-credentials).
  • Reflected origin — server echoes the request Origin back (cors-reflected-origin); critical when combined with credentials.
  • Null origin — Allow-Origin: null (cors-null-origin).
  • Wildcard origin — Allow-Origin: * without credentials (cors-wildcard).
  • Credentialed CORS — informational note when credentials are enabled (cors-credentials-enabled).
  • Wildcard methods — Allow-Methods: * (cors-methods-wildcard).

How to run it

# Live probe (sends a throwaway Origin to test reflection)
python skills/cors-auditor/auditor.py https://api.example.com

# Probe with a specific origin
python skills/cors-auditor/auditor.py https://api.example.com --origin https://evil.example

# Offline: audit a captured header block; pass --origin to test reflection
python skills/cors-auditor/auditor.py --headers-file resp.txt --origin https://evil.example

# Only fail CI on high/critical (hides the medium wildcard + info notes)
python skills/cors-auditor/auditor.py https://api.example.com --min-severity high

Exit codes: 0 clean · 1 findings reported · 2 fetch/usage error. Every reported finding fails the build. The default reports everything down to info (including cors-credentials-enabled); raise --min-severity to low/medium/high to filter advisory notes out of both the report and the exit code.

Recommended workflow for Claude

  1. Probe the endpoint (live) or audit captured headers (offline).
  2. Explain each finding and why it is exploitable (e.g. reflected origin + credentials = cross-origin data theft).
  3. Recommend an explicit origin allowlist and dropping credentials where not needed.
  4. Only test APIs the user owns or is authorized to test.

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