CVE-2025-57757

Executive Summary

CVE-2025-57757 is an information disclosure vulnerability in the Contao Open Source CMS. The flaw allows unauthorized access to news items from protected news archives via RSS feeds. When a news feed is configured to include a protected news archive, the access control mechanism fails to filter out the protected items, making them publicly available in the RSS feed output. This bypasses the intended access restrictions and exposes potentially sensitive content to unauthenticated users.

The vulnerability affects Contao versions 5.0.0 through 5.3.37 and 5.4.0 through 5.6.0. The CVSS score is 5.3 (Medium), with a vector emphasizing network-based, low-complexity exploitation without authentication. The EPSS score is 0.0%, indicating no active exploitation in the wild at the time of analysis. No public proof-of-concept code or exploit templates are available.

Supply Chain & Package Security

Contao is a PHP-based CMS distributed via Composer. The vulnerability exists in the core news module. While no direct supply chain compromise is reported, the risk of using unpatched versions is significant. Organizations should verify their Composer lock files and ensure they are not pinned to vulnerable versions. The patch is available via the official Contao repository and Composer package updates.

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 (AV): Network – The vulnerability can be exploited remotely.
• Attack Complexity (AC): Low – No special conditions or complex steps are required.
• Privileges Required (PR): None – No authentication is needed.
• User Interaction (UI): None – No user action is required.
• Scope (S): Unchanged – The exploit does not affect other components.
• Confidentiality (C): Low – Limited information disclosure (news items).
• Integrity (I): None – No data modification.
• Availability (A): None – No service disruption.

Threat Level: Medium. The vulnerability is easy to exploit but only leads to information disclosure. However, if the protected news archives contain sensitive business or personal data, the impact could be higher.

Deep Dive & Mechanics

The vulnerability resides in the RSS feed generation logic of Contao's news module. When a news feed is created, it can include one or more news archives. Contao supports access control on news archives, allowing administrators to restrict viewing to authenticated users or specific user groups. However, the RSS feed generation code does not check the access permissions of the included archives.

Root Cause: The NewsFeedModel or equivalent class iterates over all news items from the selected archives without applying access control filters. The code likely uses a query like:

$newsItems = NewsModel::findBy(['pid IN (?)'], [$archiveIds], ['order' => 'date DESC']);

This query retrieves all items from the specified archives, regardless of their protected status. The feed generation then outputs these items without checking if the current user (or the feed context) has permission to view them.

Attack Scenario:

1. An attacker identifies a Contao site with RSS feeds enabled.
2. The attacker discovers the RSS feed URL (e.g., /share/news.xml or /feed.xml).
3. The attacker accesses the feed and sees news items from archives that should be protected.
4. The attacker can then read the full content of those news items, potentially gaining access to confidential information.

Vulnerable vs. Patched Code

Vulnerable Code (Conceptual):

// In NewsFeedGenerator.php (vulnerable version)
public function generateFeed($feedId) {
    $feed = NewsFeedModel::findById($feedId);
    $archives = $feed->getArchives();
    $items = NewsModel::findByArchives($archives); // No access check
    foreach ($items as $item) {
        $this->addItemToFeed($item);
    }
}

Patched Code (Conceptual):

// In NewsFeedGenerator.php (patched version)
public function generateFeed($feedId) {
    $feed = NewsFeedModel::findById($feedId);
    $archives = $feed->getArchives();
    $accessibleArchives = array_filter($archives, function($archive) {
        return $archive->isPubliclyAccessible(); // Check access
    });
    $items = NewsModel::findByArchives($accessibleArchives);
    foreach ($items as $item) {
        $this->addItemToFeed($item);
    }
}

The patch adds a permission check on each archive before including its items in the feed. Only archives that are publicly accessible (or have no access restrictions) are included.

Exploitation & Lab Setup

Red Team (Exploitation)

Prerequisites:

• A Contao instance running a vulnerable version (5.0.0 to 5.3.37 or 5.4.0 to 5.6.0).
• At least one news archive configured as "protected" (e.g., requiring login).
• A news feed that includes that protected archive.

Steps:

1. Identify the RSS feed URL. Common paths include:
   • /share/news.xml
   • /feed.xml
   • /news.xml
   • /index.php/feed.xml
2. Use curl or a browser to access the feed:

   curl -v http://target.com/share/news.xml
   

3. Examine the XML output. Look for <item> elements that contain news from the protected archive.
4. Extract the full content of those items, including titles, descriptions, and links.

Example Output:

<rss version="2.0">
  <channel>
    <item>
      <title>Confidential Internal Announcement</title>
      <description>This is a protected news item that should not be public.</description>
      <link>http://target.com/news/confidential-announcement.html</link>
    </item>
  </channel>
</rss>

Blue Team (Detection & Defense)

Detection:

• Monitor access logs for requests to RSS feed URLs (e.g., feed.xml, news.xml).
• Look for unusual patterns, such as repeated requests to the same feed from different IPs.
• Check for the presence of protected content in feed outputs by comparing feed items with the access control list.

Defense:

• Apply the patch immediately (upgrade to 5.3.38 or 5.6.1).
• As a workaround, remove protected news archives from any news feed configuration.
• Implement additional access controls on the feed endpoint, such as IP whitelisting or authentication.
• Use a Web Application Firewall (WAF) to block automated scraping of feeds.

Indicators of Compromise (IOCs)

• Network:
  • HTTP requests to /share/news.xml, /feed.xml, /news.xml, or similar paths.
  • User-Agent strings indicating automated tools (e.g., curl, wget, python-requests).
• File System:
  • No specific file-based IOCs.
• Logs:
  • Access log entries showing 200 responses to feed URLs from unauthenticated users.
  • Error logs may show attempts to access protected archives via feed generation.

Detection Engineering

YARA Rule

rule CVE_2025_57757_Contao_Feed_Disclosure {
    meta:
        description = "Detects Contao RSS feed responses containing protected news items"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2025-57757"
        hash = "unknown"
    strings:
        $rss_start = "<rss version=\"2.0\">"
        $item_start = "<item>"
        $title = "<title>"
        $description = "<description>"
        $protected_keywords = /(confidential|internal|protected|private|restricted)/i
    condition:
        $rss_start and $item_start and $title and $description and #protected_keywords >= 1
}

Sigma Rule

title: Contao RSS Feed Information Disclosure
id: 8a4b3c2d-1e5f-6a7b-8c9d-0e1f2a3b4c5d
status: experimental
description: Detects access to Contao RSS feeds that may expose protected news items
author: Valters IT
date: 2025-04-10
references:
    - https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2025-57757
logsource:
    category: webserver
    product: apache
    service: access
detection:
    selection:
        cs-method: 'GET'
        cs-uri-stem|endswith:
            - '/share/news.xml'
            - '/feed.xml'
            - '/news.xml'
            - '/index.php/feed.xml'
    condition: selection
falsepositives:
    - Legitimate feed readers
level: medium
tags:
    - attack.t1190
    - cve.2025.57757

Suricata Rule

alert http any any -> $HOME_NET any (
    msg:"CVE-2025-57757 - Contao RSS Feed Information Disclosure";
    flow:to_server,established;
    content:"GET";
    http_method;
    content:"/share/news.xml";
    http_uri;
    sid:10000001;
    rev:1;
    metadata:attack_target Web_Server, deployment Perimeter, signature_severity Medium, created_at 2025_04_10, updated_at 2025_04_10;
)

Remediation & Mitigation

Immediate Actions:

1. Upgrade Contao to version 5.3.38 or 5.6.1 (or later).
2. If upgrade is not immediately possible, remove protected news archives from any news feed configuration.
3. Review RSS feed content to ensure no protected items have been exposed.

Long-term Measures:

• Implement regular security audits of CMS configurations.
• Use a Web Application Firewall (WAF) to monitor and block suspicious feed requests.
• Enable logging and alerting for access to feed endpoints.
• Follow the principle of least privilege for content access.

Patch Verification:

• After upgrading, verify the fix by checking that protected archives are no longer included in feeds.
• Use the following test:

  curl http://target.com/share/news.xml | grep -i "protected"
  

  If no protected content appears, the patch is effective.

Valters IT
Securing Digital Frontiers