CVE-2021-32566
📋 TL;DR
CVE-2021-32566 is an improper input validation vulnerability in Apache Traffic Server's HTTP/2 implementation that allows attackers to cause a denial-of-service (DoS) condition. The vulnerability affects Apache Traffic Server versions 7.0.0 to 7.1.12, 8.0.0 to 8.1.1, and 9.0.0 to 9.0.1. Organizations using these versions as HTTP/2 proxies or caches are at risk.
💻 Affected Systems
- Apache Traffic Server
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Complete service outage of Apache Traffic Server, disrupting all proxied/cached HTTP/2 traffic and potentially affecting downstream applications.
Likely Case
Service degradation or temporary unavailability of the Traffic Server instance, requiring restart to recover.
If Mitigated
Minimal impact with proper network segmentation and monitoring allowing quick detection and response.
🎯 Exploit Status
The vulnerability requires sending specially crafted HTTP/2 requests, which is relatively straightforward for attackers with HTTP/2 knowledge.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 7.1.13, 8.1.2, 9.0.2
Vendor Advisory: https://lists.apache.org/thread.html/ra1a41ff92a70d25bf576d7da2590575e8ff430393a3f4a0c34de4277@%3Cusers.trafficserver.apache.org%3E
Restart Required: Yes
Instructions:
1. Backup current configuration. 2. Stop Apache Traffic Server service. 3. Upgrade to patched version (7.1.13, 8.1.2, or 9.0.2). 4. Restart service. 5. Verify functionality.
🔧 Temporary Workarounds
Disable HTTP/2
linuxTemporarily disable HTTP/2 protocol support to mitigate the vulnerability while planning upgrade.
# Edit records.config and set:
CONFIG proxy.config.http2.enabled INT 0
# Then restart Traffic Server:
systemctl restart trafficserver
Rate Limiting
linuxImplement rate limiting on HTTP/2 connections to reduce DoS impact.
# Configure in records.config:
CONFIG proxy.config.http2.max_concurrent_streams_per_connection INT 100
CONFIG proxy.config.http2.initial_window_size INT 65535
🧯 If You Can't Patch
- Implement network-level protections such as WAF rules to filter suspicious HTTP/2 traffic.
- Deploy additional Traffic Server instances behind load balancer with health checks to maintain availability during attacks.
🔍 How to Verify
Check if Vulnerable:
Check Traffic Server version with: trafficserver -v. If version falls within affected ranges and HTTP/2 is enabled, system is vulnerable.Check Version:
trafficserver -vVerify Fix Applied:
After upgrade, verify version is 7.1.13, 8.1.2, or 9.0.2 with: trafficserver -v. Test HTTP/2 functionality remains operational.📡 Detection & Monitoring
Log Indicators:
- Unusual HTTP/2 connection resets
- Increased error logs related to HTTP/2 parsing
- Traffic Server process crashes or restarts
Network Indicators:
- Spike in HTTP/2 RST_STREAM frames
- Abnormal HTTP/2 header patterns
- Connection floods to Traffic Server port
SIEM Query:
source="trafficserver" AND ("HTTP/2" OR "h2") AND (error OR crash OR reset)🔗 References
- https://lists.apache.org/thread.html/ra1a41ff92a70d25bf576d7da2590575e8ff430393a3f4a0c34de4277%40%3Cusers.trafficserver.apache.org%3E
- https://www.debian.org/security/2021/dsa-4957
- https://lists.apache.org/thread.html/ra1a41ff92a70d25bf576d7da2590575e8ff430393a3f4a0c34de4277%40%3Cusers.trafficserver.apache.org%3E
- https://www.debian.org/security/2021/dsa-4957
