Getting it into your agent
It runs from inside its repository, so the clone comes first — what it calls does not travel with the file alone.
git clone --depth 1 https://github.com/JustineDevs/premortemnpx agentmods add skills/justinedevs/premortem/csrf-cross-site-request-forgeryWrote 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/justinedevs/premortem/csrf-cross-site-request-forgery)<a href="https://agentmods.dev/skills/justinedevs/premortem/csrf-cross-site-request-forgery"><img src="https://agentmods.dev/badge/skills/justinedevs/premortem/csrf-cross-site-request-forgery/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/justinedevs/premortem/csrf-cross-site-request-forgery"><img src="https://agentmods.dev/badge/skills/justinedevs/premortem/csrf-cross-site-request-forgery.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 | $0.00044 | $0.04192 |
| Opus 5 | $0.00022 | $0.02096 |
| Sonnet 5 | $0.00009 | $0.00838 |
| Haiku 4.5 | $0.00004 | $0.00419 |
Grade D, and why
csrf-cross-site-request-forgery scanned grade D with 2 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 10d 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.
Hidden instructionshighPrompt injection
Directives inside HTML comments, invisible characters or bidirectional overrides are read by the model and not by the person reviewing the file.
<!-- If server accepts GET for state-changing endpoint: --> Sends data to an external URLmediumData exfiltration
A POST to an outside endpoint may be telemetry or may be exfiltration; either way the mod talks to somewhere, and you should know where.
fetch('https://target.com/api/v1/change-email', { method: 'POST', This is a copy
100% identical to csrf-cross-site-request-forgery — 0 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 — 527 lines — stays where its author put it; the contents beside it link to each section on GitHub.
SKILL: CSRF — Cross-Site Request Forgery — Expert Attack Playbook
AI LOAD INSTRUCTION: Expert CSRF techniques. Covers modern bypass vectors (SameSite gaps, custom header flaws, tokenless bypass patterns), JSON CSRF, multipart CSRF, chaining with XSS. Base models often present only basic CSRF without covering SameSite edge cases and common broken token implementations.
0. RELATED ROUTING
Also load:
- cors cross origin misconfiguration when JSON endpoints become readable cross-origin
- oauth oidc misconfiguration when login, account linking, or callback binding relies on OAuth state
1. CORE CONCEPT
CSRF exploits a victim's active session to perform state-changing requests from the attacker's origin.
Required conditions:
- Victim is authenticated (active session cookie)
- Server identifies session via cookie only (no secondary check)
- Attacker can predict/construct the valid request
- Cookie is sent cross-origin (SameSite=None or legacy behavior)
2. FINDING CSRF TARGETS
High-value state-changing endpoints:
- Password change ← account takeover
- Email change ← account takeover
- Add admin / change role ← privilege escalation
- Bank/payment transfer ← financial impact
- OAuth app authorization ← hijack oauth flow
- Account deletion
- Two-factor auth disable
- SSH key / API key addition
- Webhook configuration
- Profile/contact info update
3. TOKEN BYPASS TECHNIQUES
No Token Present
Simplest case — form simply lacks CSRF token. Check if POST /change-email has any token. If not → trivially exploitable.
Token Not Validated (most common finding!)
Token exists in request but is never verified server-side:
Remove the _csrf_token parameter entirely → does request still succeed?
→ YES → trivial bypass
Token Tied to Session but Not to User
Step 1: Log in as UserA → obtain valid CSRF token
Step 2: Log in as UserB in other browser → obtain UserB CSRF token
Step 3: Use UserB's CSRF token in UserA's session (attacker controls UserB)
→ If server validates token exists but doesn't check if it belongs to the session → bypass
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.
- 10d ago First seen · 527 lines · 44 tokens per session scan D b837b92b54fa
csrf-cross-site-request-forgery is a skill published in the GitHub repository JustineDevs/premortem (2 stars, last pushed 1mo ago), licensed Apache-2.0. It adds 44 tokens to every session and 4,192 once invoked, about $0.0002 per session on Opus 5. A static security scan graded it D with 2 findings (hidden instructions, sends data to an external url). It is 100% identical to csrf-cross-site-request-forgery, differing in 0 lines, and is treated as a copy.
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