CVE-2021-32623
📋 TL;DR
CVE-2021-32623 is a billion laughs attack vulnerability in Opencast that allows authenticated users with ingest privileges to execute a permanent denial of service attack using a single HTTP request. This vulnerability affects Opencast versions prior to 9.6, potentially allowing attackers to completely take down the Opencast service.
💻 Affected Systems
- Opencast
📦 What is this software?
Opencast by Apereo
⚠️ Risk & Real-World Impact
Worst Case
Complete and permanent denial of service of the Opencast service, requiring system restart or reinstallation to recover.
Likely Case
Service disruption and downtime for all Opencast users, requiring administrative intervention to restore functionality.
If Mitigated
Limited impact if proper access controls restrict ingest privileges to trusted users only.
🎯 Exploit Status
Exploitation requires authenticated user with ingest privileges; single HTTP request can trigger the attack.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Opencast 9.6 and later
Vendor Advisory: https://github.com/opencast/opencast/security/advisories/GHSA-9gwx-9cwp-5c2m
Restart Required: Yes
Instructions:
1. Backup your Opencast configuration and data. 2. Upgrade to Opencast 9.6 or later. 3. Restart all Opencast services. 4. Verify the upgrade was successful.
🧯 If You Can't Patch
- Immediately restrict ingest privileges to only essential, trusted users.
- Implement network segmentation to isolate Opencast instances from untrusted networks.
🔍 How to Verify
Check if Vulnerable:
Check Opencast version: if version is below 9.6, the system is vulnerable.Check Version:
Check Opencast admin interface or configuration files for version information.Verify Fix Applied:
Verify Opencast version is 9.6 or higher and test ingest functionality with XML payloads.📡 Detection & Monitoring
Log Indicators:
- Unusually large XML parsing operations
- Memory exhaustion errors in Opencast logs
- Multiple failed ingest attempts with complex XML
Network Indicators:
- HTTP POST requests to ingest endpoints with large XML payloads
- Sudden increase in memory usage on Opencast servers
SIEM Query:
source="opencast.log" AND ("OutOfMemoryError" OR "XML parsing" AND size>100KB)🔗 References
- https://github.com/opencast/opencast/commit/8ae27da5a6f658011a5741b3210e715b0dc6213e
- https://github.com/opencast/opencast/security/advisories/GHSA-9gwx-9cwp-5c2m
- https://github.com/opencast/opencast/commit/8ae27da5a6f658011a5741b3210e715b0dc6213e
- https://github.com/opencast/opencast/security/advisories/GHSA-9gwx-9cwp-5c2m
