> 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/path-traversal/validating-the-start-of-the-path-directory-traversal.md).
# Validation du début de la traversée de répertoire
Notes sur la validation du début de la traversée de répertoire pour les laboratoires de la PortSwigger Web Security Academy, incluant le workflow d’exploitation, les tests de payloads, la validation dans Burp Suite et le contexte de remédiation.
### Traversée de chemin de fichier, validation du début du chemin
L'application transmet l'intégralité du chemin du fichier via un paramètre de requête et vérifie seulement que ce chemin **commence** correspond au dossier attendu. Cette validation est insuffisante : en ajoutant des éléments après le préfixe autorisé, il est possible d'accéder à des fichiers arbitraires.
#### **Analyse**
Le paramètre filename inclut directement un chemin absolu, par exemple :
```bash
/var/www/images
```
Si l'on essaie un contournement classique :
```bash
../../../../../etc/passwd
```
l'application le bloque.
Mais si l'on fournit **le chemin attendu**, suivi de `../` séquences pour en sortir, la validation ne détecte pas l'évasion :
Comme le chemin commence bien par `/var/www/images/`, la vérification est satisfaite, mais la résolution finale pointe en réalité vers `/etc/passwd`.
```bash
/var/www/images/../../../../../etc/passwd
```
---
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