CVE-2021-40516
📋 TL;DR
CVE-2021-40516 is an out-of-bounds read vulnerability in WeeChat's Relay plugin that allows remote attackers to crash the application via specially crafted WebSocket frames. This affects WeeChat users with the Relay plugin enabled, potentially exposing chat clients to denial of service attacks.
💻 Affected Systems
- WeeChat
📦 What is this software?
Weechat by Weechat
⚠️ Risk & Real-World Impact
Worst Case
Remote unauthenticated attacker causes WeeChat to crash, disrupting chat sessions and potentially leading to data loss if unsaved messages are present.
Likely Case
Denial of service through application crash, requiring manual restart of WeeChat to restore functionality.
If Mitigated
No impact if Relay plugin is disabled or proper network segmentation prevents access to the vulnerable service.
🎯 Exploit Status
Exploitation requires sending a malicious WebSocket frame to the vulnerable Relay plugin endpoint. No authentication is required if the service is exposed.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 3.2.1
Vendor Advisory: https://weechat.org/doc/security/
Restart Required: Yes
Instructions:
1. Update WeeChat to version 3.2.1 or later using your package manager. 2. For source installations: download latest release from weechat.org and compile. 3. Restart WeeChat after updating.
🔧 Temporary Workarounds
Disable Relay Plugin
allDisable the vulnerable Relay plugin to prevent exploitation
/plugin unload relay
Restrict Network Access
linuxConfigure firewall rules to restrict access to WeeChat Relay port (default 9001)
iptables -A INPUT -p tcp --dport 9001 -j DROP
🧯 If You Can't Patch
- Disable the Relay plugin entirely if not needed
- Implement strict network segmentation to isolate WeeChat from untrusted networks
🔍 How to Verify
Check if Vulnerable:
Check WeeChat version and verify Relay plugin is enabled: /version and /plugin info relayCheck Version:
/versionVerify Fix Applied:
Confirm version is 3.2.1 or later: /version📡 Detection & Monitoring
Log Indicators:
- WeeChat crash logs
- Segmentation fault errors in system logs
- Unexpected termination of weechat process
Network Indicators:
- Malformed WebSocket frames to Relay plugin port
- Multiple connection attempts to port 9001
SIEM Query:
process.name:"weechat" AND event.action:"crashed" OR destination.port:9001 AND network.protocol:"websocket"🔗 References
- https://github.com/weechat/weechat/commit/8b1331f98de1714bae15a9ca2e2b393ba49d735b
- https://lists.debian.org/debian-lts-announce/2021/09/msg00018.html
- https://weechat.org/doc/security/
- https://github.com/weechat/weechat/commit/8b1331f98de1714bae15a9ca2e2b393ba49d735b
- https://lists.debian.org/debian-lts-announce/2021/09/msg00018.html
- https://weechat.org/doc/security/
