> 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 répertoires
### Parcours de chemin de fichier, validation du début du chemin
L'application transmet le chemin complet du fichier via un paramètre de requête et vérifie seulement que ce chemin **commence** avec le dossier attendu. Cette validation est insuffisante : en ajoutant 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 tente un contournement classique :
```bash
../../../../../etc/passwd
```
l'application le bloque.
Mais si nous fournissons **le chemin attendu**, suivi de `../` des séquences pour sortir, la validation ne détecte pas l'évasion :
Comme le chemin commence bien par `/var/www/images/`, le contrôle est satisfait, mais la résolution finale pointe en réalité vers `/etc/passwd`.
```bash
/var/www/images/../../../../../etc/passwd
```
---
# 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/fr/web/path-traversal/validating-the-start-of-the-path-directory-traversal.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.