CVE-2020-9494
📋 TL;DR
This vulnerability in Apache Traffic Server allows attackers to send specially crafted HTTP/2 HEADERS frames that cause excessive memory allocation and thread spinning, potentially leading to denial of service. It affects Apache Traffic Server versions 6.0.0-6.2.3, 7.0.0-7.1.10, and 8.0.0-8.0.7. Organizations using these versions with HTTP/2 enabled are at risk.
💻 Affected Systems
- Apache Traffic Server
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Complete service outage due to memory exhaustion and thread spinning, making the server unresponsive to legitimate traffic.
Likely Case
Degraded performance and intermittent service disruptions as memory consumption spikes and threads become unresponsive.
If Mitigated
Minimal impact with proper monitoring and resource limits in place, though some performance degradation may still occur.
🎯 Exploit Status
Exploitation requires sending malicious HTTP/2 HEADERS frames, which can be done with standard HTTP/2 clients. The vulnerability is well-documented in security advisories.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 6.2.4, 7.1.11, 8.0.8
Vendor Advisory: https://lists.apache.org/thread.html/rf7f86917f42fdaf904d99560cba0c016e03baea6244c47efeb60ecbe%40%3Cdev.trafficserver.apache.org%3E
Restart Required: Yes
Instructions:
1. Download the patched version from Apache Traffic Server website. 2. Stop the Traffic Server service. 3. Backup configuration files. 4. Install the patched version. 5. Restart the Traffic Server service. 6. Verify the service is running correctly.
🔧 Temporary Workarounds
Disable HTTP/2
allTemporarily disable HTTP/2 protocol support to prevent exploitation while patching.
Edit traffic_server config and set 'proxy.config.http2.enabled' to 0
Restart traffic_server: traffic_server -R
Implement Rate Limiting
allConfigure rate limiting for HTTP/2 connections to reduce attack surface.
Configure connection limits in records.config: CONFIG proxy.config.http2.max_concurrent_streams_per_connection INT 100
Restart traffic_server: traffic_server -R
🧯 If You Can't Patch
- Implement network-level filtering to block or rate limit HTTP/2 traffic from untrusted sources.
- Deploy a WAF or reverse proxy in front of Traffic Server to filter malicious HTTP/2 frames.
🔍 How to Verify
Check if Vulnerable:
Check the Traffic Server version with: traffic_server -V. If version falls within affected ranges and HTTP/2 is enabled, the system is vulnerable.Check Version:
traffic_server -VVerify Fix Applied:
After patching, verify version with: traffic_server -V. Ensure version is 6.2.4+, 7.1.11+, or 8.0.8+. Test HTTP/2 functionality remains operational.📡 Detection & Monitoring
Log Indicators:
- Unusual memory consumption spikes in system logs
- Traffic Server error logs showing thread spinning or allocation failures
- Increased number of HTTP/2 connection attempts
Network Indicators:
- High volume of HTTP/2 HEADERS frames from single sources
- Abnormal HTTP/2 traffic patterns
SIEM Query:
source="traffic_server" AND ("memory allocation" OR "thread spin" OR "HTTP/2 HEADERS")🔗 References
- http://www.openwall.com/lists/oss-security/2021/03/01/2
- https://lists.apache.org/thread.html/rf7f86917f42fdaf904d99560cba0c016e03baea6244c47efeb60ecbe%40%3Cdev.trafficserver.apache.org%3E
- https://www.debian.org/security/2020/dsa-4710
- http://www.openwall.com/lists/oss-security/2021/03/01/2
- https://lists.apache.org/thread.html/rf7f86917f42fdaf904d99560cba0c016e03baea6244c47efeb60ecbe%40%3Cdev.trafficserver.apache.org%3E
- https://www.debian.org/security/2020/dsa-4710
