CVE-2021-31745
📋 TL;DR
CVE-2021-31745 is a session fixation vulnerability in Pluck-CMS that allows attackers to maintain unauthorized access even after password resets. This affects Pluck-CMS administrators because the system doesn't invalidate existing sessions when passwords change. Attackers can hijack sessions and maintain persistent access to the admin panel.
💻 Affected Systems
- Pluck-CMS
📦 What is this software?
Pluck by Pluck Cms
⚠️ Risk & Real-World Impact
Worst Case
Attackers gain persistent administrative access, allowing complete compromise of the CMS including content manipulation, plugin installation, and potential server takeover.
Likely Case
Attackers maintain unauthorized access to the admin panel after password changes, enabling content modification, user management, and potential privilege escalation.
If Mitigated
With proper session management and monitoring, impact is limited to temporary unauthorized access until sessions expire naturally.
🎯 Exploit Status
Exploitation requires initial session hijacking or fixation, but once achieved, persistence is trivial. The GitHub issue contains technical details.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 4.7.16
Vendor Advisory: https://github.com/pluck-cms/pluck/issues/99
Restart Required: No
Instructions:
1. Backup your Pluck-CMS installation. 2. Download Pluck-CMS 4.7.16 or later from the official repository. 3. Replace the existing installation files with the patched version. 4. Verify that login.php now includes session invalidation on password change.
🔧 Temporary Workarounds
Manual Session Invalidation
linuxManually invalidate all sessions after password changes by clearing session data
# Clear PHP session files
rm -rf /path/to/pluck/data/sessions/*
# Alternative: Modify login.php to add session_regenerate_id(true) after password change
Session Timeout Reduction
allReduce session lifetime to limit exposure window
# In php.ini or .htaccess
php_value session.gc_maxlifetime 1800
# Set session cookie lifetime
php_value session.cookie_lifetime 1800
🧯 If You Can't Patch
- Implement strict session monitoring and alert on unusual admin activity patterns
- Require multi-factor authentication for all admin accounts to compensate for session fixation risk
🔍 How to Verify
Check if Vulnerable:
Check if your Pluck-CMS version is 4.7.15 or earlier. Examine login.php for session invalidation logic after password change.Check Version:
Check the version.txt file in your Pluck installation directory: cat /path/to/pluck/version.txtVerify Fix Applied:
After patching, test that changing an admin password invalidates existing sessions. Attempt to use old session tokens - they should no longer work.📡 Detection & Monitoring
Log Indicators:
- Multiple successful logins from same session ID after password change
- Admin sessions persisting beyond expected lifetime after credential updates
Network Indicators:
- Unusual admin panel access patterns, especially after password reset events
SIEM Query:
source="pluck-access.log" (event="password_change" OR event="login") | stats count by session_id, user | where count > 1