CVE-2023-23923
📋 TL;DR
This Moodle vulnerability allows remote attackers to set the 'start page' preference for other users, bypassing intended access controls. Attackers can exploit this to access restricted functionality they shouldn't have permission to use. All Moodle instances with vulnerable versions are affected.
💻 Affected Systems
- Moodle
📦 What is this software?
Moodle by Moodle
Moodle by Moodle
Moodle by Moodle
Moodle by Moodle
⚠️ Risk & Real-World Impact
Worst Case
Attackers could gain administrative access to Moodle, modify courses, access sensitive student data, or disrupt educational operations.
Likely Case
Attackers access restricted course materials, modify user settings, or perform unauthorized actions within the learning management system.
If Mitigated
With proper access controls and monitoring, impact is limited to minor user preference changes that can be quickly detected and reverted.
🎯 Exploit Status
Exploitation requires some user interaction or social engineering to target specific users
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Check Moodle security advisories for specific patched versions
Vendor Advisory: https://moodle.org/mod/forum/discuss.php?d=443274
Restart Required: No
Instructions:
1. Check current Moodle version. 2. Apply Moodle security update via package manager or manual update. 3. Clear Moodle caches. 4. Verify fix by testing start page preference functionality.
🔧 Temporary Workarounds
Restrict User Preference Modification
allTemporarily disable or restrict the ability to modify start page preferences through Moodle configuration
# Edit Moodle config.php to add restrictions
# $CFG->forced_plugin_settings['user'] = array('startpage' => 'default');
🧯 If You Can't Patch
- Implement strict access controls and monitor for unauthorized preference changes
- Disable or restrict the start page preference feature entirely through configuration
🔍 How to Verify
Check if Vulnerable:
Check Moodle version against security advisories at moodle.org/securityCheck Version:
php admin/cli/check_database_schema.php | grep 'Moodle version'Verify Fix Applied:
Test if unauthorized users can modify other users' start page preferences📡 Detection & Monitoring
Log Indicators:
- Unauthorized user preference modifications in Moodle logs
- Multiple start page preference changes from single IP
Network Indicators:
- Unusual POST requests to user preference endpoints
SIEM Query:
source="moodle.log" AND "preference" AND "startpage" AND user!=current_user🔗 References
- http://git.moodle.org/gw?p=moodle.git&a=search&h=HEAD&st=commit&s=MDL-76862
- https://bugzilla.redhat.com/show_bug.cgi?id=2162549
- https://moodle.org/mod/forum/discuss.php?d=443274#p1782023
- http://git.moodle.org/gw?p=moodle.git&a=search&h=HEAD&st=commit&s=MDL-76862
- https://bugzilla.redhat.com/show_bug.cgi?id=2162549
- https://moodle.org/mod/forum/discuss.php?d=443274#p1782023
