CVE-2025-66301
📋 TL;DR
This vulnerability allows editors with limited permissions in Grav CMS to modify form processing logic by manipulating YAML frontmatter in POST requests. Attackers could change form behavior to execute unauthorized actions after user submissions. All Grav installations prior to version 1.8.0-beta.27 are affected.
💻 Affected Systems
- Grav CMS
📦 What is this software?
Grav by Getgrav
Grav by Getgrav
Grav by Getgrav
Grav by Getgrav
Grav by Getgrav
Grav by Getgrav
Grav by Getgrav
Grav by Getgrav
Grav by Getgrav
Grav by Getgrav
Grav by Getgrav
Grav by Getgrav
Grav by Getgrav
Grav by Getgrav
Grav by Getgrav
Grav by Getgrav
Grav by Getgrav
Grav by Getgrav
Grav by Getgrav
Grav by Getgrav
Grav by Getgrav
Grav by Getgrav
Grav by Getgrav
Grav by Getgrav
Grav by Getgrav
Grav by Getgrav
Grav by Getgrav
⚠️ Risk & Real-World Impact
Worst Case
Attackers could modify form processing to execute arbitrary code, leading to remote code execution, data exfiltration, or complete system compromise.
Likely Case
Unauthorized modification of form behavior leading to data manipulation, privilege escalation, or injection of malicious actions in form submissions.
If Mitigated
With proper authorization controls, impact is limited to authorized users only making legitimate form modifications.
🎯 Exploit Status
Exploitation requires authenticated editor access. The vulnerability is straightforward to exploit once access is obtained.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 1.8.0-beta.27
Vendor Advisory: https://github.com/getgrav/grav/security/advisories/GHSA-v8x2-fjv7-8hjh
Restart Required: No
Instructions:
1. Backup your Grav installation. 2. Update Grav to version 1.8.0-beta.27 or later using the built-in GPM (Grav Package Manager) or manual update. 3. Verify the update completed successfully.
🔧 Temporary Workarounds
Restrict Admin Access
allLimit access to the Grav admin panel to only trusted users who require it.
Implement Web Application Firewall
allDeploy a WAF to monitor and block suspicious POST requests to /admin/pages/ endpoints.
🧯 If You Can't Patch
- Implement strict access controls to limit who can access the Grav admin interface
- Monitor logs for suspicious POST requests to /admin/pages/ endpoints and investigate any unauthorized modifications
🔍 How to Verify
Check if Vulnerable:
Check your Grav version. If it's earlier than 1.8.0-beta.27, you are vulnerable.Check Version:
php bin/grav versionVerify Fix Applied:
After updating, verify the version is 1.8.0-beta.27 or later and test that unauthorized form modifications are properly blocked.📡 Detection & Monitoring
Log Indicators:
- Unusual POST requests to /admin/pages/{page_name} endpoints
- Modifications to form processing YAML by non-admin users
- Multiple failed authorization attempts on admin pages
Network Indicators:
- POST requests to /admin/pages/ with modified data[_json][header][form] parameters
- Unusual traffic patterns to admin endpoints
SIEM Query:
source="grav_logs" AND (uri_path="/admin/pages/*" AND http_method="POST" AND user_role="editor")