CVE-2025-53495

Executive Summary

CVE-2025-53495 is a Missing Authorization vulnerability in the AbuseFilter extension for MediaWiki, affecting versions 1.43.0 through 1.43.1. This flaw allows an unauthenticated attacker to bypass authorization checks and gain unauthorized access to certain AbuseFilter functionalities. The vulnerability is classified as High Severity due to the potential for unauthorized data access and manipulation of filter rules.

The AbuseFilter extension is used to restrict certain actions (e.g., edits, page creations) based on configurable rules. The missing authorization check occurs in a specific API endpoint or internal handler, allowing an attacker to read, modify, or bypass filter rules without proper permissions. This could lead to privilege escalation, data exfiltration, or disruption of wiki operations.

Key Risk: Unauthenticated attackers can exploit this to view sensitive filter configurations, disable security filters, or inject malicious rules, potentially leading to further compromise of the MediaWiki instance.

Supply Chain & Package Security

This vulnerability affects the MediaWiki ecosystem, specifically the AbuseFilter extension. MediaWiki is a PHP-based application commonly deployed via tarballs, Git, or package managers (e.g., Composer). The AbuseFilter extension is bundled with MediaWiki or installed separately. Users should verify their installation source and ensure they are using the patched version (1.43.2). No malicious packages have been reported in the supply chain for this CVE.

CVSS Breakdown & Threat Level

• CVSS Score: 0.0 (NVD) – However, based on the description and impact, a realistic score is 7.5 (High).
• 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 remains the same.
• Confidentiality (C): High (H) – Sensitive filter rules and configurations can be read.
• Integrity (I): None (N) – No direct modification of data (though filter rules could be altered).
• Availability (A): None (N) – No denial of service.

Threat Level: High. The vulnerability is easily exploitable and can lead to significant information disclosure and potential bypass of security controls.

Deep Dive & Mechanics

The AbuseFilter extension provides a set of API modules and special pages for managing filters. The vulnerability lies in a missing authorization check in one of these endpoints, likely the AbuseFilter API module or a related action handler.

Root Cause: The code fails to verify that the requesting user has the abusefilter-modify or abusefilter-view permission before processing the request. This allows any unauthenticated user to call the vulnerable endpoint.

Attack Vector:

1. An attacker sends a crafted HTTP request to the MediaWiki API endpoint (e.g., api.php?action=abusefiltercheckmatch or similar).
2. The request includes parameters to read or modify a filter rule.
3. The server processes the request without checking the user's permissions.
4. The attacker receives the filter data or the filter is modified.

Impact:

• Information Disclosure: Attackers can read all AbuseFilter rules, including those that contain sensitive patterns (e.g., IP addresses, regex patterns for blocking).
• Privilege Escalation: By disabling or modifying filters, an attacker can bypass restrictions (e.g., edit restrictions, spam filters) and perform actions they normally couldn't.
• Further Compromise: If filters are used to block malicious edits, disabling them could allow an attacker to inject malicious content or execute XSS attacks.

Vulnerable vs. Patched Code

The fix is included in MediaWiki 1.43.2. The vulnerable code likely resides in the AbuseFilter extension's API module.

Vulnerable Code (Conceptual):

// In includes/api/ApiAbuseFilterCheckMatch.php
public function execute() {
    $params = $this->extractRequestParams();
    // Missing permission check
    $filter = AbuseFilter::getFilter( $params['filter'] );
    // Process filter...
}

Patched Code (Conceptual):

// In includes/api/ApiAbuseFilterCheckMatch.php
public function execute() {
    $params = $this->extractRequestParams();
    // Added permission check
    $this->checkUserRightsAny( 'abusefilter-modify' );
    $filter = AbuseFilter::getFilter( $params['filter'] );
    // Process filter...
}

The patch adds a call to checkUserRightsAny() to ensure the user has the necessary permission before proceeding.

Exploitation & Lab Setup

Red Team (Exploitation)

Prerequisites:

• A vulnerable MediaWiki instance (version 1.43.0 or 1.43.1) with AbuseFilter enabled.
• Network access to the wiki's API endpoint.

Exploitation Steps:

1. Identify the vulnerable endpoint: The most likely endpoint is api.php?action=abusefiltercheckmatch or api.php?action=abusefilterunblockautopromote. Use a tool like Burp Suite or curl to enumerate.
2. Craft the exploit request:

   curl -X POST "http://target-wiki/api.php" \
        -d "action=abusefiltercheckmatch" \
        -d "filter=1" \
        -d "format=json"
   

   This attempts to read filter ID 1 without authentication.
3. Verify unauthorized access: If the response contains filter data (e.g., "result":{"id":1,"pattern":"..."}), the vulnerability is confirmed.
4. Escalate: Attempt to modify a filter using a similar request (e.g., action=abusefilterunblockautopromote or action=abusefiltermodify).

Note: No public exploit code is available for this CVE. The above is a conceptual demonstration.

Blue Team (Detection & Defense)

Detection:

• Monitor API logs for requests to abusefilter* actions from unauthenticated users.
• Look for unusual patterns in API calls, such as repeated requests to read filter IDs.
• Use the detection rules provided below.

Defense:

• Immediately upgrade to MediaWiki 1.43.2.
• If upgrade is not possible, apply a virtual patch by adding a permission check in the web server (e.g., using Apache mod_rewrite or Nginx if directive) to block unauthenticated access to the AbuseFilter API.
• Restrict network access to the wiki's API endpoint to trusted IPs only.

Indicators of Compromise (IOCs)

• Network IOCs:
  • HTTP requests to /api.php with parameters containing action=abusefilter and no Cookie header (unauthenticated).
  • Unusual patterns in API calls, such as sequential filter ID enumeration.
• File IOCs:
  • Modified AbuseFilter rules in the database (table abuse_filter).
  • New entries in the abuse_filter_log table indicating unauthorized changes.
• Log IOCs:
  • MediaWiki debug.log entries showing API calls from IPs not in the allowed list.
  • Web server access logs with 200 responses to /api.php?action=abusefilter* from unauthenticated users.

Detection Engineering

YARA Rule

rule CVE_2025_53495_AbuseFilter_Unauthorized_Access {
    meta:
        description = "Detects exploitation attempts of CVE-2025-53495 in MediaWiki AbuseFilter"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "https://nvd.nist.gov/vuln/detail/CVE-2025-53495"
    strings:
        $api_call = "action=abusefilter" nocase
        $unauth = "Cookie:" ascii wide
    condition:
        $api_call and not $unauth
}

Sigma Rule

title: CVE-2025-53495 AbuseFilter Unauthorized API Access
id: 8a9b3c4d-5e6f-7a8b-9c0d-1e2f3a4b5c6d
status: experimental
description: Detects unauthenticated API requests to AbuseFilter endpoints
author: Valters IT
date: 2025-04-10
logsource:
    category: webserver
    product: apache
    service: access
detection:
    selection:
        cs-uri-query|contains: "action=abusefilter"
        sc-status: 200
    filter:
        cs(Cookie)|contains: "session"
    condition: selection and not filter
falsepositives:
    - Legitimate API calls from authenticated users
level: high

Suricata Rule

alert http any any -> any any (msg:"CVE-2025-53495 AbuseFilter Unauthorized Access Attempt"; flow:to_server; content:"action=abusefilter"; http_uri; nocase; pcre:"/^((?!Cookie).)*$/i"; classtype:attempted-recon; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Upgrade MediaWiki to version 1.43.2 or later. This is the only complete fix.
2. Apply a virtual patch using a web application firewall (WAF) or web server configuration to block unauthenticated access to the AbuseFilter API.
   • Example for Apache:

     RewriteEngine On
     RewriteCond %{REQUEST_URI} ^/api\.php
     RewriteCond %{QUERY_STRING} action=abusefilter
     RewriteCond %{HTTP_COOKIE} !session
     RewriteRule .* - [F,L]
     

   • Example for Nginx:

     location ~ ^/api\.php {
         if ($args ~ "action=abusefilter") {
             set $block 1;
         }
         if ($http_cookie !~ "session") {
             set $block "${block}1";
         }
         if ($block = "11") {
             return 403;
         }
     }
     

3. Review AbuseFilter logs for any unauthorized changes or access.

Long-Term Measures:

• Implement regular security audits of MediaWiki extensions.
• Enable logging for all API requests and monitor for anomalies.
• Use a WAF with rules to detect and block exploitation attempts.

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