CVE-2021-41585
📋 TL;DR
An improper input validation vulnerability in Apache Traffic Server's socket connection handling allows attackers to send malicious requests that cause the server to stop accepting new connections. This affects Apache Traffic Server versions 5.0.0 through 9.1.0, potentially causing denial of service for web traffic and proxy services.
💻 Affected Systems
- Apache Traffic Server
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Complete denial of service where the server stops accepting all new connections, disrupting all web traffic and proxy services until manual restart.
Likely Case
Intermittent service disruption where the server stops accepting connections periodically, requiring monitoring and restarts to maintain availability.
If Mitigated
Minimal impact with proper network segmentation and monitoring allowing quick detection and restart of affected services.
🎯 Exploit Status
The vulnerability requires sending specially crafted network packets to the server's listening ports.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 9.1.1 and later
Vendor Advisory: https://lists.apache.org/thread/k01797hyncx53659wr3o72s5cvkc3164
Restart Required: Yes
Instructions:
1. Download Apache Traffic Server 9.1.1 or later from the official Apache website. 2. Stop the Traffic Server service. 3. Install the updated version following the official installation guide. 4. Restart the Traffic Server service.
🔧 Temporary Workarounds
Network Access Control
linuxRestrict network access to Traffic Server ports to trusted sources only using firewall rules.
iptables -A INPUT -p tcp --dport [ATS_PORT] -s [TRUSTED_NETWORK] -j ACCEPT
iptables -A INPUT -p tcp --dport [ATS_PORT] -j DROP
🧯 If You Can't Patch
- Implement rate limiting on incoming connections to reduce attack surface
- Deploy redundant Traffic Server instances behind a load balancer with health checks
🔍 How to Verify
Check if Vulnerable:
Check the Traffic Server version with 'traffic_server -V' and verify if it's between 5.0.0 and 9.1.0 inclusive.Check Version:
traffic_server -VVerify Fix Applied:
After patching, verify the version is 9.1.1 or later with 'traffic_server -V' and monitor for connection acceptance issues.📡 Detection & Monitoring
Log Indicators:
- Increased error logs related to socket connections
- Log entries showing server stopping connection acceptance
- Unusual patterns of connection attempts
Network Indicators:
- Sudden drop in successful connections to server ports
- Increased TCP connection resets
- Unusual traffic patterns to server listening ports
SIEM Query:
source="traffic_server" AND ("connection refused" OR "socket error" OR "accept failed")