CVE-2024-49593: Advanced Custom Fields XSS Vulnerability

CVE-2024-49593 Overview

A stored Cross-Site Scripting (XSS) vulnerability exists in Advanced Custom Fields (ACF) before version 6.3.9 and Secure Custom Fields before version 6.3.6.3, both popular plugins for WordPress. This vulnerability allows attackers to inject malicious JavaScript payloads that execute when administrators use the Field Group editor to modify plugin fields.

Critical Impact

Attackers can execute arbitrary JavaScript in the context of authenticated WordPress administrators, potentially leading to session hijacking, privilege escalation, or complete site compromise.

Affected Products

• Advanced Custom Fields (ACF) versions prior to 6.3.9
• Secure Custom Fields versions prior to 6.3.6.3
• WordPress installations using vulnerable versions of these plugins

Discovery Timeline

• 2024-10-17 - CVE-2024-49593 published to NVD
• 2024-11-18 - Last updated in NVD database

Technical Details for CVE-2024-49593

Vulnerability Analysis

This stored XSS vulnerability (CWE-79) affects the Field Group editor functionality within the Advanced Custom Fields and Secure Custom Fields WordPress plugins. The vulnerability arises from insufficient input sanitization when processing field data within the plugin's administrative interface.

When an attacker with the ability to create or modify field groups injects malicious JavaScript into specific field parameters, the payload is stored in the database without proper encoding. Subsequently, when another administrator accesses the Field Group editor to view or edit that field, the malicious script executes within their browser session.

The attack exploits the trust relationship between the WordPress administrative interface and stored field configuration data. Since the payload executes within an authenticated administrator session, attackers can potentially perform any action available to that administrator, including creating new admin accounts, modifying site content, or injecting additional backdoors.

Root Cause

The root cause of this vulnerability is improper output encoding in the Field Group editor interface. User-supplied input stored in field configurations is rendered without adequate sanitization or escaping, allowing HTML and JavaScript injection. The plugin fails to apply proper context-aware output encoding when displaying field data in the administrative interface, violating secure coding practices for preventing XSS attacks.

Attack Vector

The attack vector is network-based and requires an attacker to have sufficient privileges to create or modify ACF field groups. The attacker crafts a malicious field containing JavaScript code in a vulnerable parameter. When a victim administrator opens the Field Group editor and interacts with the compromised field, the stored payload executes in their browser context.

The attack flow typically involves:

1. An attacker with field group editing privileges injects a malicious XSS payload into a field configuration
2. The payload is stored in the WordPress database without proper sanitization
3. A victim administrator accesses the Field Group editor
4. The malicious JavaScript executes within the victim's authenticated session
5. The attacker gains the ability to perform actions as the victim administrator

Detection Methods for CVE-2024-49593

Indicators of Compromise

• Unexpected JavaScript code or HTML tags present in ACF field group configurations stored in the wp_posts or related ACF tables
• Unusual administrative actions performed by legitimate accounts without user knowledge
• New administrator accounts created without authorization
• Modified plugin files or unexpected JavaScript inclusions in WordPress themes

Detection Strategies

• Monitor WordPress database tables associated with ACF for suspicious content patterns including <script> tags, javascript: URIs, or event handler attributes
• Implement Web Application Firewall (WAF) rules to detect XSS payloads in POST requests to ACF administrative endpoints
• Review WordPress audit logs for unusual field group modifications or suspicious administrative activity
• Deploy SentinelOne's Singularity XDR to detect behavioral anomalies in WordPress environments

Monitoring Recommendations

• Enable comprehensive logging for WordPress administrative actions, particularly field group creation and modification events
• Configure alerts for database queries containing potential XSS payloads targeting ACF configuration tables
• Implement Content Security Policy (CSP) headers to mitigate the impact of successful XSS exploitation
• Regularly audit user accounts with field group editing privileges

How to Mitigate CVE-2024-49593

Immediate Actions Required

• Update Advanced Custom Fields to version 6.3.9 or later immediately
• Update Secure Custom Fields to version 6.3.6.3 or later if using the secure variant
• Review existing field group configurations for any suspicious or unexpected JavaScript content
• Audit WordPress administrator accounts for any unauthorized access or suspicious activity

Patch Information

The vulnerability has been addressed in Advanced Custom Fields version 6.3.9 and Secure Custom Fields version 6.3.6.3. Administrators should update to these patched versions as soon as possible. For those using the free version of ACF who wish to use the WP Engine alternative update mechanism, detailed installation and upgrade instructions are available in the ACF Blog Installation Guide. The complete changelog documenting security fixes can be found in the ACF Change Log.

Workarounds

• Restrict access to the Field Group editor to only trusted administrators until the patch can be applied
• Implement strict Content Security Policy (CSP) headers to limit script execution sources
• Use a Web Application Firewall (WAF) with XSS filtering rules to block common injection patterns
• Regularly backup WordPress databases to enable rapid recovery if compromise is detected

# Verify installed ACF version via WP-CLI
wp plugin list --name=advanced-custom-fields --fields=name,version,status

# Update ACF to the latest patched version
wp plugin update advanced-custom-fields

# Check for suspicious content in ACF field configurations
wp db query "SELECT ID, post_title FROM wp_posts WHERE post_type='acf-field-group' AND (post_content LIKE '%<script%' OR post_content LIKE '%javascript:%')"