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.
npx skills add miru-zero/zero-brain --skill cors-cross-origin-misconfigurationgit clone --depth 1 https://github.com/miru-zero/zero-brainWrote 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.
[](https://agentmods.dev/skills/miru-zero/zero-brain/cors-cross-origin-misconfiguration)<a href="https://agentmods.dev/skills/miru-zero/zero-brain/cors-cross-origin-misconfiguration"><img src="https://agentmods.dev/badge/skills/miru-zero/zero-brain/cors-cross-origin-misconfiguration/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.
<a href="https://agentmods.dev/skills/miru-zero/zero-brain/cors-cross-origin-misconfiguration"><img src="https://agentmods.dev/badge/skills/miru-zero/zero-brain/cors-cross-origin-misconfiguration.svg" alt="Reviewed on agentmods" width="80" height="20"></a>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.
| Model | Per session | Once invoked |
|---|---|---|
| Fable 5.1 | $0.00043 | $0.02391 |
| Opus 5 | $0.00022 | $0.01196 |
| Sonnet 5 | $0.00009 | $0.00478 |
| Haiku 4.5 | $0.00004 | $0.00239 |
Grade A, and why
cors-cross-origin-misconfiguration scanned grade A with 1 finding 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 8d 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.
Makes network callslowCapability
Not a fault in itself. Listed so you know the mod talks to something, and to what.
curl -H "Origin: https://evil.com" https://target.com/api/data -I This is a copy
98% identical to cors-cross-origin-misconfiguration — 4 lines differ, which has more behind it and is treated as the original. This page carries a canonical link to it rather than competing with it.
How it starts
The opening of the file, as written. The whole thing — 270 lines — stays where its author put it; the contents beside it link to each section on GitHub.
SKILL: CORS Misconfiguration — Credentialed Origins, Reflection, and Trust Boundary Errors
AI LOAD INSTRUCTION: Use this skill when browsers can access authenticated APIs cross-origin. Focus on reflected origins, credentialed requests, wildcard trust, parser mistakes, and origin allowlist bypasses. For JSONP hijacking deep dives, same-origin policy internals, honeypot de-anonymization, and CORS vs JSONP comparison, load the companion SCENARIOS.md.
Extended Scenarios
Also load SCENARIOS.md when you need:
- JSONP hijacking complete attack scenario — watering hole +
<script>cross-origin data theft - Honeypot de-anonymization via JSONP — use social platform JSONP endpoints to identify anonymous visitors
- Same-origin policy deep dive — protocol/hostname/port definition,
document.domainsubdomain relaxation and its security risks - CORS vs JSONP technical comparison — methods, error handling, credential behavior, migration path
- CORS exploitation payloads — reflected origin with
credentials: include, null origin via sandboxed iframe - Dual-site attack lab pattern — localhost:8981 (target) + localhost:8982 (attacker) testing setup
1. WHEN TO LOAD THIS SKILL
Load when:
- Responses contain
Access-Control-Allow-Origin,Access-Control-Allow-Credentials, or preflight headers - A browser-based attack path might read authenticated API responses
- JSON endpoints appear protected from CSRF but are readable cross-origin
2. HIGH-VALUE MISCONFIGURATION CHECKS
| Theme | What to Check |
|---|---|
| wildcard with credentials | Access-Control-Allow-Origin: * plus credential support or equivalent broken behavior |
| reflected origin | server echoes arbitrary Origin |
| weak allowlist | suffix, prefix, substring, regex, or mixed-case matching errors |
null origin |
acceptance of sandboxed, file, or serialized origins |
| preflight trust | overbroad methods and headers |
| internal API exposure | admin or tenant data readable cross-origin |
What ships with it
1 file 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.
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.
- 8d ago First seen · 270 lines · 43 tokens per session scan A 09bdae8963d8
cors-cross-origin-misconfiguration is a skill published in the GitHub repository miru-zero/zero-brain (0 stars, last pushed 21d ago), licensed MIT. It adds 43 tokens to every session and 2,391 once invoked, about $0.0002 per session on Opus 5. A static security scan graded it A with 1 finding (makes network calls). It is 98% identical to cors-cross-origin-misconfiguration, differing in 4 lines, and is treated as a copy.
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