CVE-2024-5024

Executive Summary

CVE-2024-5024 is a Reflected Cross-Site Scripting (XSS) vulnerability in the Memberpress WordPress plugin, affecting all versions up to and including 1.11.29. The flaw exists in the mepr_screenname and mepr_key parameters, which are insufficiently sanitized and escaped. An unauthenticated attacker can inject arbitrary web scripts that execute in the context of a victim's browser if the victim clicks a crafted link. The CVSS score is 6.1 (Medium), and the EPSS score is 0.0%, indicating low exploitation likelihood at this time. No public exploit code or patch details are available.

Supply Chain & Package Security

This vulnerability affects a WordPress plugin distributed via the official WordPress plugin repository. Users should verify the integrity of their plugin files and ensure they are obtained from trusted sources. The lack of a patch increases supply chain risk for sites using unmaintained or outdated versions.

CVSS Breakdown & Threat Level

• Attack Vector (AV): Network (N) – The attack is carried out over the network.
• Attack Complexity (AC): Low (L) – No special conditions are required.
• Privileges Required (PR): None (N) – No authentication needed.
• User Interaction (UI): Required (R) – The victim must click a malicious link.
• Scope (S): Changed (C) – The vulnerability impacts resources beyond the vulnerable component.
• Confidentiality (C): Low (L) – Limited data exposure possible.
• Integrity (I): Low (L) – Limited ability to modify content.
• Availability (A): None (N) – No impact on availability.

Threat Level: Medium. The requirement for user interaction reduces the risk, but the lack of a patch and the potential for phishing campaigns make this a concern for WordPress site administrators.

Deep Dive & Mechanics

The vulnerability is a classic Reflected XSS. The Memberpress plugin uses the mepr_screenname and mepr_key parameters in its URL handling. When these parameters are echoed back into the page without proper sanitization or output escaping, an attacker can inject malicious JavaScript.

Attack Flow:

1. An attacker crafts a malicious URL containing JavaScript payloads in the mepr_screenname or mepr_key parameters.
2. The attacker tricks a victim (e.g., via phishing email or social media) into clicking the link.
3. The victim's browser sends a request to the vulnerable WordPress site.
4. The server processes the request and reflects the malicious input into the HTML response.
5. The victim's browser executes the injected script, which can steal cookies, redirect to malicious sites, or perform actions on behalf of the victim.

Root Cause: The plugin fails to use WordPress's built-in escaping functions (e.g., esc_attr(), esc_html(), wp_kses()) on user-supplied input before outputting it.

Vulnerable vs. Patched Code

Since no official patch is available, the following is a hypothetical fix based on standard WordPress security practices.

Vulnerable Code (Conceptual):

// In a template or function file
echo '<input type="hidden" name="mepr_screenname" value="' . $_GET['mepr_screenname'] . '" />';

Patched Code (Conceptual):

// Properly escape the output
echo '<input type="hidden" name="mepr_screenname" value="' . esc_attr($_GET['mepr_screenname']) . '" />';

The patched version uses esc_attr() to ensure any HTML or JavaScript in the parameter is safely encoded.

Exploitation & Lab Setup

Red Team

Lab Setup:

1. Install a local WordPress instance (e.g., using Docker or XAMPP).
2. Install Memberpress plugin version 1.11.29.
3. Create a test page that uses the vulnerable parameters.

Proof-of-Concept (PoC) URL:

http://target-site.com/?mepr_screenname=<script>alert('XSS')</script>

Advanced Payload:

http://target-site.com/?mepr_key=<img src=x onerror=alert(document.cookie)>

Note: No public exploit code is available. The above are standard XSS payloads for testing.

Blue Team

Detection:

• Monitor web server logs for requests containing suspicious patterns in the mepr_screenname or mepr_key parameters.
• Look for <script>, <img onerror>, or other HTML event handlers in query strings.
• Use WAF rules to block common XSS payloads.

Mitigation:

• Apply a virtual patch via WAF (e.g., ModSecurity rule to block <script> in those parameters).
• Disable the plugin until an official patch is released.
• Educate users not to click suspicious links.

Indicators of Compromise (IOCs)

• URL Patterns: Requests containing mepr_screenname= or mepr_key= with encoded or raw HTML/JavaScript.
• Log Entries: HTTP 200 responses to URLs with XSS payloads in the query string.
• Client-Side: Unexpected JavaScript execution, redirects, or cookie theft.

Detection Engineering

YARA Rule

rule CVE_2024_5024_XSS {
    meta:
        description = "Detects Reflected XSS attempts against Memberpress plugin"
        author = "Valters IT"
        date = "2024-05-20"
        reference = "CVE-2024-5024"
    strings:
        $param1 = "mepr_screenname="
        $param2 = "mepr_key="
        $xss1 = /<script[^>]*>/
        $xss2 = /onerror\s*=\s*['"]/
        $xss3 = /onload\s*=\s*['"]/
    condition:
        (any of ($param*)) and (any of ($xss*))
}

Sigma Rule

title: Reflected XSS via Memberpress Plugin
id: 8a4b3c2d-1e5f-4a7b-9c8d-0e1f2a3b4c5d
status: experimental
description: Detects potential XSS attempts targeting CVE-2024-5024
author: Valters IT
logsource:
    category: webserver
    product: apache
detection:
    selection:
        c-uri|contains:
            - 'mepr_screenname='
            - 'mepr_key='
        c-uri|re:
            - '<script'
            - 'onerror='
            - 'onload='
    condition: selection
falsepositives:
    - Legitimate use of these parameters with safe input
level: high

Suricata Rule

alert http any any -> any any (msg:"CVE-2024-5024 Reflected XSS in Memberpress"; flow:to_server,established; content:"mepr_screenname="; nocase; http_uri; pcre:"/(<script|onerror|onload)/i"; sid:1000001; rev:1;)

Remediation & Mitigation

1. Immediate Action: Disable the Memberpress plugin until a patch is released.
2. Virtual Patching: Implement WAF rules to block XSS payloads in the mepr_screenname and mepr_key parameters.
3. User Education: Warn administrators and users about phishing attacks exploiting this vulnerability.
4. Monitor: Review web server logs for exploitation attempts.
5. Update: Watch the Memberpress plugin page for an official update and apply it immediately when available.

Valters IT
Securing Digital Frontiers