CVE-2023-28332
📋 TL;DR
This CVE describes a cross-site scripting (XSS) vulnerability in Moodle's algebra filter feature. When the algebra filter is enabled but not properly configured (e.g., required binaries are missing), it fails to sanitize user input, allowing attackers to inject malicious scripts. This affects Moodle instances with the algebra filter enabled but non-functional.
💻 Affected Systems
- Moodle
📦 What is this software?
Moodle by Moodle
Moodle by Moodle
Moodle by Moodle
Moodle by Moodle
Moodle by Moodle
Moodle by Moodle
Moodle by Moodle
Moodle by Moodle
⚠️ Risk & Real-World Impact
Worst Case
Attackers could execute arbitrary JavaScript in victims' browsers, potentially stealing session cookies, performing actions as authenticated users, or redirecting to malicious sites.
Likely Case
Limited XSS exploitation affecting users who view content containing malicious algebra filter input, potentially leading to session hijacking or credential theft.
If Mitigated
With proper input validation and output encoding, the risk is eliminated; the vulnerability only exists when the algebra filter is misconfigured.
🎯 Exploit Status
Exploitation requires the algebra filter to be enabled but broken, and attacker needs ability to inject malicious content
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Check Moodle security advisories for specific patched versions
Vendor Advisory: https://moodle.org/mod/forum/discuss.php?d=445064
Restart Required: No
Instructions:
1. Update Moodle to the latest patched version. 2. Alternatively, disable the algebra filter if not needed. 3. Ensure required binaries (mimetex) are properly installed if using algebra filter.
🔧 Temporary Workarounds
Disable Algebra Filter
allTurn off the algebra filter feature in Moodle administration
Navigate to Site administration > Plugins > Filters > Manage filters, then disable 'Algebra notation'
Install Required Binaries
linuxEnsure mimetex or other required binaries are properly installed and configured
Install mimetex package: sudo apt-get install mimetex (Debian/Ubuntu)
Configure Moodle to use the installed binary
🧯 If You Can't Patch
- Disable the algebra filter entirely in Moodle administration
- Implement web application firewall (WAF) rules to block XSS payloads
🔍 How to Verify
Check if Vulnerable:
Check if algebra filter is enabled in Moodle administration and verify if required binaries are missingCheck Version:
Check Moodle version in Site administration > General > NotificationsVerify Fix Applied:
Verify Moodle version is updated to patched release and algebra filter either disabled or properly configured📡 Detection & Monitoring
Log Indicators:
- Unusual algebra filter usage patterns
- Failed algebra filter processing attempts
Network Indicators:
- Suspicious JavaScript payloads in algebra filter content
SIEM Query:
Search for algebra filter errors or suspicious content in web application logs🔗 References
- https://bugzilla.redhat.com/show_bug.cgi?id=2179419
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/3QZN34VSF4HTCW3C3ZP2OZYSLYUKADPF/
- https://moodle.org/mod/forum/discuss.php?d=445064
- https://bugzilla.redhat.com/show_bug.cgi?id=2179419
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/3QZN34VSF4HTCW3C3ZP2OZYSLYUKADPF/
- https://moodle.org/mod/forum/discuss.php?d=445064
