CVE-2020-27813
📋 TL;DR
CVE-2020-27813 is an integer overflow vulnerability in websocket frame length handling that allows attackers to cause denial of service on HTTP servers with websocket support. This affects applications using the Gorilla WebSocket library. The vulnerability can crash servers by sending specially crafted websocket frames.
💻 Affected Systems
- Gorilla WebSocket library
- Applications using Gorilla WebSocket
- Red Hat products using affected versions
📦 What is this software?
Websocket by Gorillatoolkit
⚠️ Risk & Real-World Impact
Worst Case
Complete server crash leading to sustained denial of service, potentially affecting multiple applications on the same server.
Likely Case
Service disruption through server crashes or resource exhaustion, requiring manual restart of affected services.
If Mitigated
Limited impact with proper network segmentation and monitoring, but still vulnerable to targeted attacks.
🎯 Exploit Status
The vulnerability is straightforward to exploit by sending malformed websocket frames. Public advisories provide enough technical detail for exploitation.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Gorilla WebSocket 1.4.0 and later
Vendor Advisory: https://github.com/gorilla/websocket/security/advisories/GHSA-jf24-p9p9-4rjh
Restart Required: Yes
Instructions:
1. Update Gorilla WebSocket dependency to version 1.4.0 or later. 2. Update go.mod to require github.com/gorilla/websocket v1.4.0 or higher. 3. Rebuild and redeploy affected applications. 4. Restart services using the updated library.
🔧 Temporary Workarounds
WebSocket Connection Filtering
linuxImplement network filtering to block or limit websocket connections from untrusted sources.
iptables -A INPUT -p tcp --dport 80 -m string --string "Upgrade: websocket" --algo bm -j DROP
iptables -A INPUT -p tcp --dport 443 -m string --string "Upgrade: websocket" --algo bm -j DROP
Rate Limiting WebSocket Connections
allImplement connection rate limiting to reduce impact of denial of service attempts.
# Configure in application or using reverse proxy like nginx: limit_conn_zone $binary_remote_addr zone=ws:10m;
limit_conn ws 10;
🧯 If You Can't Patch
- Implement strict network segmentation to isolate websocket servers from untrusted networks
- Deploy Web Application Firewall (WAF) with websocket protection rules
🔍 How to Verify
Check if Vulnerable:
Check go.mod or vendor dependencies for Gorilla WebSocket version. If version is below 1.4.0, the system is vulnerable.Check Version:
grep gorilla/websocket go.mod | grep -o 'v[0-9.]\+'Verify Fix Applied:
Verify Gorilla WebSocket version is 1.4.0 or higher in go.mod and that the application has been rebuilt with the updated dependency.📡 Detection & Monitoring
Log Indicators:
- Unexpected server crashes or restarts
- High volume of websocket connection attempts
- Error logs containing websocket frame parsing errors
Network Indicators:
- Unusual websocket traffic patterns
- Multiple websocket connections from single sources
- Malformed websocket frames in packet captures
SIEM Query:
source="websocket.log" AND ("crash" OR "panic" OR "out of memory") OR (event_type="connection" AND protocol="websocket" AND count > 1000 per src_ip)🔗 References
- https://bugzilla.redhat.com/show_bug.cgi?id=1902111
- https://github.com/gorilla/websocket/security/advisories/GHSA-jf24-p9p9-4rjh
- https://lists.debian.org/debian-lts-announce/2021/01/msg00008.html
- https://lists.debian.org/debian-lts-announce/2023/05/msg00012.html
- https://bugzilla.redhat.com/show_bug.cgi?id=1902111
- https://github.com/gorilla/websocket/security/advisories/GHSA-jf24-p9p9-4rjh
- https://lists.debian.org/debian-lts-announce/2021/01/msg00008.html
- https://lists.debian.org/debian-lts-announce/2023/05/msg00012.html
