CVE-2025-57756

Executive Summary

CVE-2025-57756 is an information disclosure vulnerability in the Contao Open Source CMS. The flaw affects protected content elements that are rendered as fragments. When the front end search feature is enabled, these protected elements are inadvertently indexed and become publicly searchable, exposing sensitive data to unauthorized users. The vulnerability impacts Contao versions starting from 4.9.14 up to, but not including, 4.13.56, 5.3.38, and 5.6.1. The CVSS score is 5.3 (Medium), and the EPSS probability is 0.0%, indicating a low likelihood of exploitation in the wild. No public proof-of-concept or exploit code is available at this time.

Supply Chain & Package Security

This vulnerability is specific to the Contao CMS ecosystem. Contao is a PHP-based open source CMS distributed via Composer. The vulnerability does not directly affect the supply chain of packages like NPM, PyPI, Go, or Ruby. However, organizations using Contao should verify their dependency versions and ensure they are updated to the patched releases.

CVSS Breakdown & Threat Level

• CVSS Score: 5.3 (Medium)
• Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N
• Attack Vector: Network
• Attack Complexity: Low
• Privileges Required: None
• User Interaction: None
• Scope: Unchanged
• Confidentiality Impact: Low
• Integrity Impact: None
• Availability Impact: None

The vulnerability is exploitable remotely without authentication or user interaction. The primary risk is the exposure of protected content, which could include sensitive information such as member-only pages, internal documents, or draft content.

Deep Dive & Mechanics

Contao uses a fragment-based rendering system for content elements. Protected content elements are intended to be visible only to authenticated users with appropriate permissions. However, when the front end search feature indexes content, it processes these fragments without checking access controls. As a result, the search index includes the text of protected elements, making them discoverable via the public search functionality.

The root cause lies in the search indexing logic, which does not enforce access control checks on content elements rendered as fragments. The search index is built by crawling the site, and the crawler does not respect the protection status of individual elements.

Vulnerable vs. Patched Code

The vulnerable code is in the search indexing module. The exact code changes are not publicly available, but the patch likely involves adding access control checks during the indexing process.

Vulnerable Code (Conceptual):

// In the search indexer, content elements are indexed without checking protection
foreach ($contentElements as $element) {
    $indexer->addToIndex($element->getText());
}

Patched Code (Conceptual):

// After the patch, the indexer checks if the element is protected before indexing
foreach ($contentElements as $element) {
    if (!$element->isProtected()) {
        $indexer->addToIndex($element->getText());
    }
}

Exploitation & Lab Setup

Red Team

1. Setup: Deploy a vulnerable Contao instance (version 4.9.14 to 4.13.55, 5.3.0 to 5.3.37, or 5.4.0 to 5.6.0) with the front end search enabled.
2. Create Protected Content: Create a protected content element (e.g., a member-only article) and ensure it is rendered as a fragment.
3. Trigger Indexing: Use the front end search feature or trigger a search index rebuild.
4. Exploit: Perform a search query that matches the protected content. The search results will include the protected element, revealing its content to unauthenticated users.

Example Search Query:

GET /search?q=sensitive+keyword HTTP/1.1
Host: vulnerable-contao-site.com

Blue Team

1. Detection: Monitor search logs for queries that return protected content. Look for patterns where unauthenticated users access search results that should be restricted.
2. Mitigation: Disable the front end search feature as a workaround. Apply the patch by updating Contao to version 4.13.56, 5.3.38, or 5.6.1.
3. Verification: After patching, verify that protected content is no longer indexed by performing a search as an unauthenticated user.

Indicators of Compromise (IOCs)

• Search Logs: Unauthenticated search queries that return results containing protected content.
• Index Files: The search index files (e.g., in var/search/) containing text from protected elements.
• Database Entries: The tl_search table may contain entries for protected content.

Example IOC (Search Log Entry):

192.168.1.100 - - [01/Jan/2025:12:00:00 +0000] "GET /search?q=confidential HTTP/1.1" 200 1234

Detection Engineering

YARA Rule

rule CVE_2025_57756_Contao_InfoDisclosure {
    meta:
        description = "Detects Contao search index files containing protected content"
        author = "Valters IT"
        date = "2025-01-01"
        reference = "CVE-2025-57756"
    strings:
        $protected = "protected" nocase
        $search_index = "tl_search" nocase
    condition:
        $protected and $search_index
}

Sigma Rule

title: CVE-2025-57756 - Contao Protected Content Exposure via Search
id: 12345678-1234-1234-1234-123456789012
status: experimental
description: Detects unauthenticated search queries that may expose protected content in Contao CMS
author: Valters IT
date: 2025-01-01
logsource:
    category: webserver
    product: apache
detection:
    selection:
        c-uri|contains: "/search?q="
        sc-status: 200
    condition: selection
falsepositives:
    - Legitimate search queries for public content
level: medium

Suricata Rule

alert http any any -> any any (msg:"CVE-2025-57756 - Contao Protected Content Exposure via Search"; flow:to_server; content:"/search?q="; http_uri; classtype:attempted-recon; sid:1000001; rev:1;)

Remediation & Mitigation

1. Immediate Workaround: Disable the front end search feature in the Contao backend settings.
2. Patch: Update Contao to version 4.13.56, 5.3.38, or 5.6.1.
3. Verification: After patching, rebuild the search index and verify that protected content is no longer publicly searchable.
4. Long-term: Implement additional access control checks on search indexing and consider using a dedicated search service that respects permissions.

Valters IT