> 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/es/web/path-traversal/validating-the-start-of-the-path-directory-traversal.md).
# Validación del inicio del recorrido de directorios de ruta
### Recorrido de rutas de archivos, validación del inicio de la ruta
La aplicación transmite toda la ruta del archivo mediante un parámetro de consulta y solo comprueba que esta ruta **empieza** coincida con la carpeta esperada. Esta validación es insuficiente: añadiendo después del prefijo permitido, es posible acceder a archivos arbitrarios.
#### **Análisis**
El parámetro filename incluye directamente una ruta absoluta, por ejemplo:
```bash
/var/www/images
```
Si uno intenta un cruce clásico:
```bash
../../../../../etc/passwd
```
la aplicación lo bloquea.
Pero si proporcionamos **la ruta esperada**, seguida de `../` secuencias para salir, la validación no detecta la escapada:
Como la ruta empieza bien con `/var/www/images/`, la comprobación se cumple, pero la resolución final en realidad apunta a `/etc/passwd`.
```bash
/var/www/images/../../../../../etc/passwd
```
---
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