CVE-2024-9385

Executive Summary

CVE-2024-9385 is a Reflected Cross-Site Scripting (XSS) vulnerability in the Themify Builder plugin for WordPress, affecting all versions up to and including 7.6.2. The flaw arises from the insecure use of add_query_arg without proper escaping on URLs, allowing unauthenticated attackers to inject arbitrary web scripts. Successful exploitation requires user interaction (e.g., clicking a crafted link), leading to script execution in the victim's browser within the context of the WordPress site. This can result in session hijacking, credential theft, or defacement. As a WordPress plugin vulnerability, it is critical to update the plugin or apply a virtual patch.

Supply Chain & Package Security

This vulnerability affects a WordPress plugin distributed via the official WordPress plugin repository. No supply chain compromise has been reported, but users should verify plugin integrity and update from trusted sources only.

CVSS Breakdown & Threat Level

• CVSS Score: 6.1 (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
• User Interaction: Required
• Scope: Changed
• Confidentiality Impact: Low
• Integrity Impact: Low
• Availability Impact: None

Threat Level: Medium. Exploitation is straightforward but requires user interaction. The impact is limited to script execution in the user's session.

Deep Dive & Mechanics

The vulnerability exists in the add_query_arg function usage within the Themify Builder plugin. In PHP, add_query_arg builds a URL by appending query parameters. When user-supplied input (e.g., via $_SERVER['REQUEST_URI'] or $_GET parameters) is passed to add_query_arg without escaping, an attacker can inject malicious JavaScript code into the generated URL. This URL is then reflected back to the user (e.g., in a redirect or link), leading to XSS.

The vulnerable code likely resembles:

$url = add_query_arg( 'return', $_GET['return'], home_url() );
echo '<a href="' . $url . '">Click here</a>';

An attacker can craft a URL like:

https://victim.com/?return=javascript:alert(document.cookie)

When the victim clicks the link, the JavaScript executes.

Vulnerable vs. Patched Code

Vulnerable Code (<= 7.6.2):

$url = add_query_arg( 'return', $_GET['return'], home_url() );
echo '<a href="' . $url . '">Go Back</a>';

Patched Code (Hypothetical):

$return_url = esc_url( add_query_arg( 'return', esc_url_raw( $_GET['return'] ), home_url() ) );
echo '<a href="' . $return_url . '">Go Back</a>';

The patch uses esc_url() and esc_url_raw() to sanitize the URL and prevent script injection.

Exploitation & Lab Setup

Red Team (Exploitation)

1. Setup: Install WordPress with Themify Builder <= 7.6.2 on a local server.
2. Craft Payload: Create a malicious URL:

   http://localhost/wp-admin/?return=javascript:alert('XSS')
   

3. Deliver: Send the link to a victim (e.g., via email or social engineering).
4. Execute: When the victim clicks the link, the JavaScript executes in their browser.

Example Exploit URL:

http://victim-site.com/?return=%22%3E%3Cscript%3Ealert(1)%3C/script%3E

Blue Team (Detection & Defense)

• Monitor Logs: Look for unusual query parameters containing return= with JavaScript or HTML tags.
• Web Application Firewall (WAF): Block requests with return parameter containing <script> or javascript:.
• User Education: Train users not to click suspicious links.

Indicators of Compromise (IOCs)

• URL Patterns: Requests containing ?return= followed by encoded JavaScript or HTML.
• Log Entries: HTTP requests with return parameter containing <script>, onerror, javascript:, or data: URIs.
• File Hashes: N/A (plugin files unchanged).
• Network Traffic: Outbound connections to attacker-controlled domains (if payload exfiltrates data).

Detection Engineering

YARA Rule

rule CVE_2024_9385_Themify_XSS {
    meta:
        description = "Detects reflected XSS attempts against Themify Builder plugin"
        author = "Valters IT"
        date = "2024-10-01"
        reference = "CVE-2024-9385"
    strings:
        $xss1 = /return=.*?<script/i
        $xss2 = /return=.*?javascript:/i
        $xss3 = /return=.*?onerror/i
        $xss4 = /return=.*?alert\(/i
    condition:
        any of them
}

Sigma Rule

title: Reflected XSS Attempt Against Themify Builder
id: 7a8b9c0d-1e2f-3a4b-5c6d-7e8f9a0b1c2d
status: experimental
description: Detects reflected XSS attempts targeting CVE-2024-9385
author: Valters IT
logsource:
    category: webserver
    product: apache
detection:
    selection:
        cs-method: GET
        cs-uri-query|contains: 'return='
        cs-uri-query|re: '(?:<script|javascript:|onerror|alert\()'
    condition: selection
falsepositives:
    - Legitimate use of 'return' parameter with safe values
level: high

Suricata Rule

alert http any any -> any any (msg:"CVE-2024-9385 Themify Builder Reflected XSS Attempt"; flow:to_server; content:"return="; http_uri; pcre:"/return=.*?(?:<script|javascript:|onerror|alert\()/i"; classtype:web-application-attack; sid:1000001; rev:1;)

Remediation & Mitigation

1. Immediate: Disable the Themify Builder plugin until a patch is available.
2. Virtual Patch: Use a WAF to block requests containing return= with suspicious patterns.
3. Update: Apply the official patch when released (check WordPress plugin repository).
4. Code Fix: Ensure all uses of add_query_arg are wrapped with esc_url().
5. User Training: Educate users to avoid clicking untrusted links.

Valters IT
Securing Digital Frontiers