CVE-2019-20041
📋 TL;DR
This vulnerability allows attackers to bypass WordPress input sanitization using HTML5 colon named entities, enabling cross-site scripting (XSS) attacks. Any WordPress site running versions before 5.3.1 is affected, potentially allowing malicious JavaScript execution in visitors' browsers.
💻 Affected Systems
- WordPress
📦 What is this software?
Wordpress by Wordpress
⚠️ Risk & Real-World Impact
Worst Case
Attackers could execute arbitrary JavaScript in users' browsers, leading to session hijacking, credential theft, content defacement, or malware distribution.
Likely Case
Cross-site scripting attacks where attackers inject malicious scripts that execute when users visit compromised pages.
If Mitigated
Limited impact if proper content security policies and input validation are already implemented.
🎯 Exploit Status
Exploitation requires user interaction (visiting malicious page) but the bypass technique is simple and well-documented.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: WordPress 5.3.1 and later
Vendor Advisory: https://wordpress.org/news/2019/12/wordpress-5-3-1-security-and-maintenance-release/
Restart Required: No
Instructions:
1. Backup your WordPress site. 2. Update WordPress to version 5.3.1 or later via Dashboard > Updates. 3. Verify update completed successfully. 4. Clear any caching plugins/CDN caches.
🔧 Temporary Workarounds
Input Sanitization Filter
allAdd custom filter to sanitize HTML5 colon entities before wp_kses processing
Add custom PHP filter function to theme's functions.php or custom plugin
🧯 If You Can't Patch
- Implement strict Content Security Policy (CSP) headers to limit script execution
- Use Web Application Firewall (WAF) rules to block javascript: patterns
🔍 How to Verify
Check if Vulnerable:
Check WordPress version in Dashboard > Updates or via wp-admin/about.phpCheck Version:
wp core version (if WP-CLI installed) or check wp-includes/version.phpVerify Fix Applied:
Verify WordPress version is 5.3.1 or higher and test input sanitization with javascript: test cases📡 Detection & Monitoring
Log Indicators:
- Unusual POST requests containing javascript: patterns
- Multiple failed sanitization attempts
Network Indicators:
- HTTP requests with javascript: in parameters
- Suspicious script injection patterns
SIEM Query:
web_requests WHERE url CONTAINS 'javascript:' OR parameters CONTAINS 'javascript:'🔗 References
- https://github.com/WordPress/wordpress-develop/commit/b1975463dd995da19bb40d3fa0786498717e3c53
- https://lists.debian.org/debian-lts-announce/2020/01/msg00010.html
- https://seclists.org/bugtraq/2020/Jan/8
- https://wordpress.org/news/2019/12/wordpress-5-3-1-security-and-maintenance-release/
- https://www.debian.org/security/2020/dsa-4599
- https://www.debian.org/security/2020/dsa-4677
- https://github.com/WordPress/wordpress-develop/commit/b1975463dd995da19bb40d3fa0786498717e3c53
- https://lists.debian.org/debian-lts-announce/2020/01/msg00010.html
- https://seclists.org/bugtraq/2020/Jan/8
- https://wordpress.org/news/2019/12/wordpress-5-3-1-security-and-maintenance-release/
- https://www.debian.org/security/2020/dsa-4599
- https://www.debian.org/security/2020/dsa-4677
