CVE-2020-27605
📋 TL;DR
CVE-2020-27605 is a critical vulnerability in BigBlueButton that allows remote code execution through malicious EPS files. Attackers can exploit Ghostscript's weak sandbox to execute arbitrary code on the server. All BigBlueButton instances up to version 2.2.28 that process uploaded documents are affected.
💻 Affected Systems
- BigBlueButton
📦 What is this software?
Bigbluebutton by Bigbluebutton
⚠️ Risk & Real-World Impact
Worst Case
Full server compromise allowing attackers to execute arbitrary commands, access sensitive data, and pivot to other systems in the network.
Likely Case
Remote code execution leading to data theft, installation of backdoors, or disruption of BigBlueButton services.
If Mitigated
Limited impact if proper file upload restrictions and network segmentation are in place, though RCE risk remains.
🎯 Exploit Status
Exploitation requires uploading a malicious EPS file, which can be done by any user with upload permissions.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 2.2.29 and later
Vendor Advisory: https://github.com/bigbluebutton/bigbluebutton/releases/tag/v2.2.29
Restart Required: Yes
Instructions:
1. Backup your BigBlueButton configuration and data. 2. Update to version 2.2.29 or later using your package manager. 3. Restart all BigBlueButton services. 4. Verify the update was successful.
🔧 Temporary Workarounds
Disable EPS file uploads
allPrevent processing of EPS files by disabling upload functionality for EPS documents.
Modify BigBlueButton configuration to reject EPS file uploads at the application level.
Update Ghostscript
linuxUpdate Ghostscript to a version with improved sandboxing if available.
apt-get update && apt-get upgrade ghostscript
yum update ghostscript
🧯 If You Can't Patch
- Implement strict network segmentation to isolate BigBlueButton servers from critical systems.
- Deploy web application firewall (WAF) rules to block EPS file uploads and monitor for exploitation attempts.
🔍 How to Verify
Check if Vulnerable:
Check BigBlueButton version: if version is 2.2.28 or earlier, the system is vulnerable.Check Version:
dpkg -l | grep bigbluebutton | grep -E '^ii' | awk '{print $3}'Verify Fix Applied:
Verify BigBlueButton version is 2.2.29 or later and test that EPS file uploads are properly handled.📡 Detection & Monitoring
Log Indicators:
- Unusual EPS file uploads
- Ghostscript process crashes or errors
- Suspicious command execution in system logs
Network Indicators:
- Unexpected outbound connections from BigBlueButton server
- Large EPS file uploads
SIEM Query:
source="bigbluebutton" AND (file_type="eps" OR process="ghostscript")