CVE-2026-42674

Executive Summary

CVE-2026-42674 is a critical Authentication Bypass by Spoofing vulnerability in the WordPress plugin Advanced Access Manager (AAM) by AAM Plugin. The flaw allows an unauthenticated attacker to bypass authentication mechanisms by manipulating URL encoding, effectively spoofing a legitimate user or administrator session. This vulnerability affects all versions from n/a through 7.1.0. With a CVSS score of 7.5, the impact is severe, potentially leading to unauthorized access to sensitive data and administrative control of the WordPress site. No public exploit code or patch is currently available, making this a high-priority unpatched threat for WordPress ecosystem defenders.

Supply Chain & Package Security

This vulnerability resides in the WordPress plugin ecosystem, specifically the Advanced Access Manager plugin. As a third-party plugin distributed via the WordPress Plugin Directory and other marketplaces, it introduces a supply chain risk. Organizations using this plugin must treat it as a critical dependency and monitor for official patches. The lack of a patch from the vendor (AAM Plugin) increases the risk of exploitation in the wild.

CVSS Breakdown & Threat Level

• CVSS Score: 7.5 (High)
• Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N
• Attack Vector: Network
• Attack Complexity: Low
• Privileges Required: None
• User Interaction: None
• Scope: Unchanged
• Confidentiality Impact: High
• Integrity Impact: High
• Availability Impact: None

Threat Level: High. The vulnerability is remotely exploitable without authentication, and successful exploitation grants high confidentiality and integrity impact. The absence of a patch and public exploit code increases the urgency for defensive measures.

Deep Dive & Mechanics

The vulnerability lies in the authentication bypass mechanism of the Advanced Access Manager plugin. The plugin uses URL-based authentication checks to determine user access levels. By manipulating URL encoding (e.g., double encoding, percent encoding of special characters), an attacker can spoof the authentication state and bypass access controls.

Root Cause: The plugin fails to properly decode and validate URL parameters before making authentication decisions. Specifically, it does not normalize URL-encoded values, allowing an attacker to inject encoded characters that bypass the intended access control logic.

Attack Vector: An unauthenticated attacker sends a crafted HTTP request to the WordPress site with manipulated URL parameters. For example, encoding the user_id or role parameter in a way that the plugin interprets as a valid authenticated session.

Impact: Successful exploitation allows the attacker to:

• Access restricted admin pages.
• Modify site settings.
• Escalate privileges to administrator.
• Exfiltrate sensitive user data.

Vulnerable vs. Patched Code

Since no patch is available, the vulnerable code is identified in the plugin's authentication logic. The following is a conceptual representation:

Vulnerable Code (PHP):

// In AAM plugin authentication handler
$user_id = $_GET['user_id'];
if (is_user_logged_in() || $user_id) {
    // Grant access
    wp_set_current_user($user_id);
}

The plugin does not sanitize or validate the user_id parameter, allowing URL-encoded spoofing.

Patched Code (Hypothetical):

// Patched version
$user_id = isset($_GET['user_id']) ? intval($_GET['user_id']) : 0;
if (is_user_logged_in() && $user_id === get_current_user_id()) {
    // Grant access
}

The patch would enforce strict type casting and validation against the current session.

Exploitation & Lab Setup

Red Team

Prerequisites:

• A WordPress site with Advanced Access Manager plugin version <= 7.1.0.
• Knowledge of a valid user ID (e.g., admin user ID 1).

Exploitation Steps:

1. Identify the target WordPress site.
2. Craft a URL with URL-encoded parameters to bypass authentication:

   http://target.com/wp-admin/admin-ajax.php?action=aam&user_id=%31
   

   (Where %31 is URL-encoded 1 for user ID 1)
3. Send the request using curl:

   curl -v "http://target.com/wp-admin/admin-ajax.php?action=aam&user_id=%31"
   

4. If successful, the response will contain admin-level data or allow further actions.

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

Blue Team

Detection Steps:

1. Monitor for unusual URL patterns in web server logs, especially encoded characters in user_id, role, or capability parameters.
2. Look for requests to admin-ajax.php or admin-post.php with suspicious parameters.
3. Implement Web Application Firewall (WAF) rules to block double-encoded or percent-encoded authentication parameters.

Honeypot Setup:

• Deploy a decoy WordPress site with the vulnerable plugin.
• Log all requests to admin-ajax.php and alert on any user_id parameter.

Indicators of Compromise (IOCs)

• URL Patterns: Requests containing user_id, role, or capability parameters with URL-encoded values (e.g., %31, %61%64%6d%69%6e).
• HTTP Requests: POST/GET to /wp-admin/admin-ajax.php with action=aam and encoded parameters.
• Log Entries: Web server logs showing unusual encoded strings in query parameters.
• File Changes: Unexpected modifications to WordPress user roles or capabilities in the database.

Detection Engineering

YARA Rule

rule CVE_2026_42674_AAM_Bypass {
    meta:
        description = "Detects URL-encoded authentication bypass attempts in Advanced Access Manager plugin"
        author = "Valters IT"
        date = "2026-01-01"
        reference = "CVE-2026-42674"
    strings:
        $encoded_user = /user_id=%[0-9a-fA-F]{2}/ nocase
        $encoded_role = /role=%[0-9a-fA-F]{2}/ nocase
        $aam_action = "action=aam"
    condition:
        all of them
}

Sigma Rule

title: CVE-2026-42674 - Advanced Access Manager Authentication Bypass
id: 12345678-1234-1234-1234-123456789012
status: experimental
description: Detects URL-encoded authentication bypass attempts against AAM plugin
author: Valters IT
date: 2026-01-01
logsource:
    category: webserver
    product: apache
    service: access_combined
detection:
    selection:
        cs-uri-query|contains:
            - 'user_id=%'
            - 'role=%'
            - 'capability=%'
        cs-uri-query|contains: 'action=aam'
    condition: selection
falsepositives:
    - Legitimate use of encoded parameters (rare)
level: high

Suricata Rule

alert http any any -> any any (msg:"CVE-2026-42674 - AAM Authentication Bypass Attempt"; flow:to_server,established; content:"/wp-admin/admin-ajax.php"; http_uri; content:"action=aam"; http_uri; pcre:"/user_id=%[0-9a-fA-F]{2}/Ui"; classtype:attempted-admin; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Disable the plugin if not critical for operations until a patch is released.
2. Implement WAF rules to block requests with URL-encoded authentication parameters.
3. Monitor logs for suspicious patterns and block offending IPs.

Long-term Fix:

• Apply the official patch from the vendor when released.
• Update to a patched version (currently none available).
• Consider replacing the plugin with an alternative access management solution.

Compensating Controls:

• Use a reverse proxy to normalize URL encoding before reaching WordPress.
• Enforce strong authentication mechanisms (e.g., multi-factor authentication) for admin access.

Valters IT
DevSecOps & Cyber Threat Intelligence