CVE-2021-24159
📋 TL;DR
This vulnerability in the Contact Form 7 Style WordPress plugin allows attackers to inject malicious JavaScript through the custom CSS feature due to lack of sanitization and nonce protection. Attackers can trick administrators into clicking malicious links to execute cross-site request forgery (CSRF) attacks, potentially compromising affected WordPress sites. All sites using Contact Form 7 Style plugin versions up to 3.1.9 are vulnerable.
💻 Affected Systems
- Contact Form 7 Style WordPress Plugin
📦 What is this software?
Contact Form 7 by Rocklobster
⚠️ Risk & Real-World Impact
Worst Case
Site takeover through admin account compromise leading to complete website defacement, data theft, malware distribution, or ransomware deployment.
Likely Case
Malicious JavaScript injection leading to session hijacking, credential theft, or redirecting visitors to phishing/malware sites.
If Mitigated
Attack fails due to proper CSRF protection, input validation, or administrator security awareness preventing the initial click.
🎯 Exploit Status
Exploitation requires social engineering to trick an administrator into clicking a malicious link. The vulnerability is well-documented in security advisories.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: None - vulnerability was never patched
Vendor Advisory: https://wpscan.com/vulnerability/363182f1-9fda-4363-8f6a-be37c4c07aa9
Restart Required: No
Instructions:
1. Remove Contact Form 7 Style plugin completely. 2. Find alternative contact form styling solutions. 3. The plugin was abandoned and never received a security patch.
🔧 Temporary Workarounds
Remove Vulnerable Plugin
allCompletely uninstall Contact Form 7 Style plugin as no patch exists
wp plugin delete contact-form-7-style
Or delete via WordPress admin panel
Implement CSRF Protection
allAdd nonce verification to all plugin forms and AJAX requests
Requires custom code modification: wp_nonce_field() and wp_verify_nonce() implementation
🧯 If You Can't Patch
- Disable plugin immediately and use alternative contact form styling solutions
- Implement web application firewall (WAF) rules to block malicious CSS/JS injection attempts
🔍 How to Verify
Check if Vulnerable:
Check WordPress admin panel > Plugins > Contact Form 7 Style. If version is 3.1.9 or lower, you are vulnerable.Check Version:
wp plugin get contact-form-7-style --field=versionVerify Fix Applied:
Verify plugin is completely removed from /wp-content/plugins/ directory and no longer appears in WordPress admin📡 Detection & Monitoring
Log Indicators:
- POST requests to /wp-admin/admin-ajax.php with action=cf7s_save_custom_css
- Unusual CSS content containing JavaScript tags or event handlers
- Multiple failed admin login attempts followed by CSS update requests
Network Indicators:
- HTTP requests containing malicious JavaScript in CSS parameters
- Traffic patterns showing CSRF attacks against admin endpoints
SIEM Query:
source="wordpress.log" AND ("cf7s_save_custom_css" OR "contact-form-7-style") AND ("script" OR "javascript" OR "onclick" OR "onload")🔗 References
- https://wpscan.com/vulnerability/363182f1-9fda-4363-8f6a-be37c4c07aa9
- https://www.wordfence.com/blog/2021/02/unpatched-vulnerability-50000-wp-sites-must-find-alternative-for-contact-form-7-style/
- https://wpscan.com/vulnerability/363182f1-9fda-4363-8f6a-be37c4c07aa9
- https://www.wordfence.com/blog/2021/02/unpatched-vulnerability-50000-wp-sites-must-find-alternative-for-contact-form-7-style/
