CVE-2021-42076
📋 TL;DR
This vulnerability allows an attacker to cause memory exhaustion (denial of service) in Barrier software by sending long TCP messages. It affects both the server-side barriers component and the client-side barrierc component. Users running Barrier versions before 2.3.4 are vulnerable.
💻 Affected Systems
- Barrier
📦 What is this software?
Barrier by Barrier Project
⚠️ Risk & Real-World Impact
Worst Case
Complete service disruption through memory exhaustion, potentially causing the Barrier service to crash and become unavailable.
Likely Case
Denial of service affecting keyboard/mouse sharing functionality, requiring service restart.
If Mitigated
Minimal impact if patched or network controls prevent malicious TCP connections.
🎯 Exploit Status
Exploitation requires network access to Barrier's TCP port (default 24800). No authentication needed to send TCP messages.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 2.3.4
Vendor Advisory: https://github.com/debauchee/barrier/releases/tag/v2.3.4
Restart Required: Yes
Instructions:
1. Download Barrier 2.3.4 or later from official GitHub releases. 2. Stop Barrier service. 3. Install/upgrade to version 2.3.4+. 4. Restart Barrier service.
🔧 Temporary Workarounds
Network Segmentation
allRestrict network access to Barrier's TCP port (default 24800) to trusted hosts only.
# Example firewall rule (Linux): sudo iptables -A INPUT -p tcp --dport 24800 -s trusted_ip -j ACCEPT
# Example firewall rule (Windows): New-NetFirewallRule -DisplayName "Barrier Restrict" -Direction Inbound -LocalPort 24800 -RemoteAddress trusted_ip -Protocol TCP -Action Allow
🧯 If You Can't Patch
- Implement strict network access controls to limit which systems can connect to Barrier's TCP port.
- Monitor Barrier process memory usage and restart service if abnormal consumption is detected.
🔍 How to Verify
Check if Vulnerable:
Check Barrier version: On Linux/macOS run 'barrier --version' or 'barrierc --version'. On Windows check About in GUI. If version is below 2.3.4, you are vulnerable.Check Version:
barrier --version 2>&1 | head -1Verify Fix Applied:
Confirm version is 2.3.4 or higher using version check command. Test Barrier functionality remains operational.📡 Detection & Monitoring
Log Indicators:
- Barrier process crashes or restarts
- High memory usage by barrier/barrierc processes
- Error messages about memory allocation failures
Network Indicators:
- Unusually large TCP packets to Barrier port 24800
- Multiple rapid connections to Barrier port
SIEM Query:
process_name="barrier" AND (event_type="crash" OR memory_usage>threshold)