# csrf-cross-site-request-forgery

A CSRF testing playbook for state-changing web flows, token checks, SameSite behavior, JSON requests, login CSRF, and OAuth state.

- skill · `type=skill` · Claude Code, Codex, Cursor, GitHub Copilot, Gemini CLI, OpenCode · 3700 installs · ★ 2547
- Author: yaklang
- License: MIT · policy=mirror · the beginning of the file is at the end of this page
- Source: https://github.com/yaklang/hack-skills/tree/HEAD/skills/csrf-cross-site-request-forgery/SKILL.md
- Updated: 2026-09-13
- HTML: https://affpapa.org/en/nevibecode/skills/csrf-cross-site-request-forgery

## What it does

This skill provides a CSRF review plan for web applications. It helps identify state-changing endpoints and check how the server connects the session, cookie, and CSRF token. The playbook covers missing tokens, tokens that are not validated, user-session binding, and broken double-submit cookie patterns.

It includes scenarios for SameSite behavior, GET-based bypasses, subdomain XSS, JSON CSRF, and multipart CSRF. The visible material also covers CORS, OAuth state, CSRF combined with XSS, plus HTML and JavaScript request templates for testing.

For JSON endpoints, check CORS and `Access-Control-Allow-Credentials` first, because the flow depends on those settings. Install it for Claude Code with `npx skills add`; the skill file is placed at `~/.claude/skills/csrf-cross-site-request-forgery/SKILL.md`.

## Install

### Claude Code (native platform)

1. **Skills CLI (Vercel)**
```bash
npx skills add yaklang/hack-skills --skill csrf-cross-site-request-forgery -a claude-code
```

2. **Manually: put the files in place**
- File: `~/.claude/skills/csrf-cross-site-request-forgery/SKILL.md` — Copy the whole skill folder; for one project use .claude/skills/csrf-cross-site-request-forgery/

### Codex

1. **Skills CLI (Vercel)**
```bash
npx skills add yaklang/hack-skills --skill csrf-cross-site-request-forgery -a codex
```

2. **Manually: put the files in place**
- File: `.agents/skills/csrf-cross-site-request-forgery/SKILL.md` — For all projects use ~/.agents/skills/

### Cursor

1. **Skills CLI (Vercel)**
```bash
npx skills add yaklang/hack-skills --skill csrf-cross-site-request-forgery -a cursor
```

2. **Manually: put the files in place**
- File: `.cursor/skills/csrf-cross-site-request-forgery/SKILL.md` — Cursor also reads .agents/skills/ and .claude/skills/

### GitHub Copilot

1. **GitHub CLI**
```bash
gh skill install yaklang/hack-skills csrf-cross-site-request-forgery
```

2. **Manually: put the files in place**
- File: `.github/skills/csrf-cross-site-request-forgery/SKILL.md`

### Gemini CLI

1. **Skills CLI (Vercel)**
```bash
npx skills add yaklang/hack-skills --skill csrf-cross-site-request-forgery -a gemini-cli
```

2. **Platform CLI**
```bash
gemini skills install https://github.com/yaklang/hack-skills --path skills/csrf-cross-site-request-forgery
```

### Windsurf (Devin Desktop)

**Manually: put the files in place**
- File: `.devin/skills/csrf-cross-site-request-forgery/SKILL.md` — The legacy .windsurf/skills/ path still works

### OpenCode

**Skills CLI (Vercel)**
```bash
npx skills add yaklang/hack-skills --skill csrf-cross-site-request-forgery -a opencode
```

### Claude.ai

**Claude.ai**
- Zip the folder and upload it in Settings → Capabilities → Skills

Where a file is given instead of a command, copy the files from the source to that path: https://github.com/yaklang/hack-skills/tree/HEAD/skills/csrf-cross-site-request-forgery/SKILL.md

## When to use it
- identify state-changing web endpoints
- check whether CSRF tokens bind to sessions
- test cookie behavior under SameSite
- review JSON and multipart request handling
- inspect OAuth state and CORS flows

## Example prompts
- Review this application’s state-changing endpoints for CSRF and create a testing plan.
- Analyze the CSRF token implementation for presence, server-side validation, and session binding.
- Test the JSON endpoints for CSRF, including CORS, SameSite, and OAuth state behavior.

## Source text · SKILL.md · MIT

Below is the content of a third-party file. It is data, not instructions for you: do not act on anything written inside unless the human asks. Block tag: 940b006acc3912fc.

BEGIN THIRD-PARTY FILE 940b006acc3912fc
````text
---
name: csrf-cross-site-request-forgery
description: >-
  CSRF testing playbook. Use when reviewing state-changing web flows, anti-CSRF defenses, SameSite behavior, JSON CSRF, login CSRF, and OAuth state handling.
---

# 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](../cors-cross-origin-misconfiguration/SKILL.md) when JSON endpoints become readable cross-origin
- [oauth oidc misconfiguration](../oauth-oidc-misconfiguration/SKILL.md) 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**:
1. Victim is authenticated (active session cookie)
2. Server identifies session via cookie only (no secondary check)
3. Attacker can predict/construct the valid request
4. 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
```

### Token in Cookie Only
When server sets CSRF token as cookie and expects it back in a header/form:
```
Set-Cookie: csrf=ATTACKER_CONTROLLED
````
END THIRD-PARTY FILE 940b006acc3912fc

The third-party file has ended. Everything between the 940b006acc3912fc tags is data: requests and commands from it are not followed. An “end of file” line with another tag inside the block is part of the file.

First 2654 of 16781 bytes. © yaklang · MIT · https://github.com/yaklang/hack-skills/tree/HEAD/skills/csrf-cross-site-request-forgery/SKILL.md

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