Contao, Cross-Site Scripting (XSS), CVE-2025-XXXX (Critical)

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How the Mentioned CVE Works:

The vulnerability (CVE-2025-XXXX) in Contao arises due to insufficient validation of SVG files uploaded by users. SVG files can contain embedded JavaScript code, which is executed when the file is rendered in the browser. In affected versions of Contao (4.0.0 to 4.13.53, 5.3.0 to 5.3.29, and 5.4.0 to 5.5.5), malicious users can upload SVG files containing XSS payloads. When these files are processed by the backend or displayed on the frontend, the embedded JavaScript executes, potentially allowing attackers to steal session cookies, deface websites, or perform actions on behalf of authenticated users. This vulnerability is particularly critical because it can be exploited without user interaction, making it a high-risk issue.

DailyCVE Form:

Platform: Contao
Version: 4.0.0 – 4.13.53, 5.3.0 – 5.3.29, 5.4.0 – 5.5.5
Vulnerability: XSS via SVG
Severity: Critical
Date: Mar 18, 2025

What Undercode Say:

Exploitation:

  1. Craft Malicious SVG: Create an SVG file with embedded JavaScript, e.g., <script>alert('XSS')</script>.
  2. Upload SVG: Exploit the vulnerability by uploading the malicious SVG to the Contao backend or frontend.
  3. Trigger Execution: The JavaScript executes when the SVG is rendered, compromising user sessions or performing unauthorized actions.

Protection:

  1. Update Contao: Upgrade to patched versions (4.13.54, 5.3.30, or 5.5.6).
  2. Restrict File Types: Remove `svg` and `svgz` from allowed uploads in config.yaml: 
    contao:
editable_files: [bash]
  3. Input Validation: Implement server-side validation to sanitize SVG content before rendering.

Commands:

1. Check Contao Version:

php bin/console contao:version

2. Update Contao:

composer require contao/core-bundle:4.13.54

Code Snippets:

1. Sanitize SVG Uploads:

$svgContent = file_get_contents($_FILES[bash][bash]);
if (preg_match('/

<script/i', $svgContent)) {
throw new Exception('Malicious SVG detected.');
}

2. Disable SVG Uploads:

$allowedTypes = [bash];
if (!in_array($_FILES[bash][bash], $allowedTypes)) {
throw new Exception('Invalid file type.');
}

Analytics:

– Affected Users: All Contao users with file upload functionality.
– Exploit Complexity: Low (requires minimal technical knowledge).
– Impact: High (potential for full system compromise).
– Mitigation Difficulty: Medium (requires configuration changes or updates).

References:

– [bash](https://contao.org/en/security-advisories/cross-site-scripting-through-svg-uploads)
– [bash](https://github.com/advisories)

References:

Reported By: https://github.com/advisories/GHSA-vqqr-fgmh-f626
Extra Source Hub:
Undercode

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