CVE-2025-53499

Executive Summary

CVE-2025-53499 is a Missing Authorization vulnerability in the AbuseFilter extension for MediaWiki, the open-source wiki platform used by Wikipedia and countless other sites. The flaw allows an unauthenticated attacker to bypass authorization checks, leading to Unauthorized Access to certain AbuseFilter functionalities. This could enable an attacker to view, modify, or bypass abuse filters, potentially allowing malicious edits, spam, or vandalism to go undetected.

The vulnerability affects MediaWiki versions 1.43.0 and 1.43.1. The Wikimedia Foundation has released version 1.43.2 which contains the fix. No public proof-of-concept (PoC) or exploit code has been released at this time, and the EPSS score is 0.0%, indicating a low immediate exploitation likelihood. However, given the widespread deployment of MediaWiki, the risk of targeted attacks remains.

Supply Chain & Package Security

This vulnerability is specific to the MediaWiki ecosystem, which is a PHP-based application. It is not a package manager (NPM, PyPI, Go, Ruby) issue. The fix is delivered through the official MediaWiki release channel.

CVSS Breakdown & Threat Level

• CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N
• Base Score: 6.5 (Medium)
• Attack Vector: Network (AV:N) – The vulnerability can be exploited remotely.
• Attack Complexity: Low (AC:L) – No special conditions are required.
• Privileges Required: None (PR:N) – No authentication is needed.
• User Interaction: None (UI:N) – No user action is required.
• Scope: Unchanged (S:U) – The vulnerable component and the impacted component are the same.
• Confidentiality Impact: Low (C:L) – Limited information disclosure (e.g., filter rules).
• Integrity Impact: Low (I:L) – Limited modification of filter rules.
• Availability Impact: None (A:N) – No denial of service.

Threat Level: Medium. While the CVSS score is moderate, the ability to bypass abuse filters can have significant downstream effects on content integrity.

Deep Dive & Mechanics

The AbuseFilter extension allows wiki administrators to create custom filters that automatically detect and block problematic edits (e.g., spam, vandalism). The vulnerability lies in how the extension handles authorization for certain API endpoints or internal actions.

Root Cause: A missing authorization check in one or more API modules or special pages within the AbuseFilter extension. This allows an unauthenticated user to perform actions that should require specific user rights (e.g., abusefilter-modify, abusefilter-view).

Attack Vector:

1. An attacker sends a crafted HTTP request to a vulnerable MediaWiki endpoint (e.g., api.php?action=abusefilter... or a special page URL).
2. The server processes the request without verifying the user's permissions.
3. The attacker can then:
   • View existing abuse filter rules (information disclosure).
   • Modify or disable filters (integrity impact).
   • Bypass filters by altering their conditions.

Impact: A successful attack could allow malicious actors to bypass content moderation, leading to the publication of spam, malware links, or defacement on the wiki.

Vulnerable vs. Patched Code

The specific code change is not publicly available in a diff format, but the fix is included in the MediaWiki 1.43.2 release. The general pattern of the fix is to add an authorization check (e.g., $this->checkUserRightsAny( 'abusefilter-modify' )) before executing sensitive operations.

Vulnerable Code (Conceptual):

// In some API module or special page
public function execute() {
    // No permission check
    $this->getResult()->addValue( null, 'filters', $this->getAllFilters() );
}

Patched Code (Conceptual):

public function execute() {
    // Added authorization check
    if ( !$this->getUser()->isAllowed( 'abusefilter-view' ) ) {
        throw new PermissionsError( 'abusefilter-view' );
    }
    $this->getResult()->addValue( null, 'filters', $this->getAllFilters() );
}

Exploitation & Lab Setup

Red Team (Offensive)

Prerequisites:

• A target running MediaWiki 1.43.0 or 1.43.1 with the AbuseFilter extension enabled.
• Network access to the wiki's API or web interface.

Exploitation Steps:

1. Identify the target: Use Shodan or Google dorks to find vulnerable MediaWiki instances.
2. Enumerate API endpoints: Send a request to api.php?action=help&modules=abusefilter to list available modules.
3. Attempt unauthorized access: Try to access a sensitive module without authentication. For example:

   GET /w/api.php?action=abusefiltercheck&filter=1&user=test&title=Main_Page&text=spam
   

   If the response returns filter results without requiring login, the instance is vulnerable.
4. Modify filters: If the abusefilter module allows modification without auth, an attacker could disable or alter filters:

   POST /w/api.php?action=abusefiltermodify&filterid=1&newfilter=...
   

Note: No public exploit code is available. This is a conceptual demonstration.

Blue Team (Defensive)

Detection:

• Monitor for unusual API requests to api.php with action=abusefilter* parameters from unauthenticated users.
• Look for spikes in 403 Forbidden errors followed by successful 200 OK responses on AbuseFilter endpoints.
• Check web server logs for requests to /w/api.php?action=abusefilter* without a valid session cookie.

Hunting:

• Search for any modifications to abuse filters that occurred without a corresponding user session.
• Review recent changes to the abuse_filter and abuse_filter_log database tables.

Indicators of Compromise (IOCs)

• Network:
  • HTTP requests to /w/api.php?action=abusefilter* without a Cookie header or with an invalid session.
  • Unusual POST requests to /w/api.php?action=abusefiltermodify from unknown IPs.
• Host:
  • Unexpected changes to the abuse_filter database table.
  • Log entries in MediaWiki's exception.log or debug.log related to PermissionsError or AbuseFilter exceptions.
• File:
  • Modified files in the extensions/AbuseFilter/ directory (if an attacker gained write access).

Detection Engineering

YARA Rule

rule Detect_CVE_2025_53499_Exploit_Attempt {
    meta:
        description = "Detects HTTP requests attempting to exploit CVE-2025-53499 in MediaWiki AbuseFilter"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2025-53499"
    strings:
        $api_call = "action=abusefilter" nocase
        $modify = "abusefiltermodify" nocase
        $check = "abusefiltercheck" nocase
        $no_auth = "Cookie:" nocase
    condition:
        $api_call and ($modify or $check) and not $no_auth
}

Sigma Rule

title: CVE-2025-53499 AbuseFilter Unauthorized Access Attempt
id: 8a4b3c2d-1e5f-4a7b-9c8d-0e1f2a3b4c5d
status: experimental
description: Detects attempts to exploit missing authorization in MediaWiki AbuseFilter extension
author: Valters IT
date: 2025-04-10
references:
    - https://nvd.nist.gov/vuln/detail/CVE-2025-53499
logsource:
    category: webserver
    product: apache
    service: access_combined
detection:
    selection:
        cs-method: 'GET' or 'POST'
        cs-uri-query|contains: 'action=abusefilter'
        cs-uri-query|contains: 
            - 'abusefiltermodify'
            - 'abusefiltercheck'
            - 'abusefilterview'
    filter:
        cs(Cookie): '*'  # Presence of a cookie indicates authentication
    condition: selection and not filter
falsepositives:
    - Legitimate admin actions (should have a valid session)
level: high

Suricata Rule

alert http any any -> any any (msg:"CVE-2025-53499 MediaWiki AbuseFilter Unauthorized Access Attempt"; flow:to_server; content:"GET"; http_method; content:"/w/api.php"; http_uri; content:"action=abusefilter"; http_uri; content:"!Cookie"; http_header; nocase; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Upgrade MediaWiki to version 1.43.2 or later. This is the official fix.
2. If immediate upgrade is not possible, disable the AbuseFilter extension temporarily:
   • Remove or rename the extensions/AbuseFilter directory.
   • Or comment out wfLoadExtension( 'AbuseFilter' ); in LocalSettings.php.

Long-term Mitigations:

• Implement a Web Application Firewall (WAF) rule to block unauthenticated requests to api.php with action=abusefilter*.
• Enforce strict authentication for all API actions. Consider using OAuth or session-based authentication.
• Regularly audit MediaWiki extensions and apply security patches promptly.
• Monitor the MediaWiki security mailing list for future advisories.

Workaround (if patching is delayed):

• Add the following to .htaccess (Apache) or a similar configuration to restrict access to the AbuseFilter API:

  RewriteEngine On
  RewriteCond %{QUERY_STRING} action=abusefilter [NC]
  RewriteCond %{HTTP_COOKIE} !.*session.* [NC]
  RewriteRule ^ - [F,L]
  

Valters IT
Securing Digital Frontiers