CVE-2024-35296
📋 TL;DR
Apache Traffic Server versions 8.0.0-8.1.10 and 9.0.0-9.2.4 have a vulnerability where specially crafted Accept-Encoding headers can bypass cache lookups, forcing requests to be forwarded to origin servers. This affects all users running vulnerable versions of Apache Traffic Server as a reverse proxy or caching server. The issue allows potential denial of service and increased origin server load.
💻 Affected Systems
- Apache Traffic Server
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Attackers could cause complete cache bypass, overwhelming origin servers with repeated requests leading to denial of service and increased operational costs.
Likely Case
Increased origin server load and degraded performance due to cache misses, potentially leading to service degradation.
If Mitigated
Minimal impact with proper rate limiting and origin server capacity planning, though cache efficiency would still be reduced.
🎯 Exploit Status
Exploitation requires sending HTTP requests with malformed Accept-Encoding headers, which is trivial to implement.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 8.1.11 or 9.2.5
Vendor Advisory: https://lists.apache.org/thread/c4mcmpblgl8kkmyt56t23543gp8v56m0
Restart Required: Yes
Instructions:
1. Download Apache Traffic Server 8.1.11 or 9.2.5 from official sources. 2. Stop the Traffic Server service. 3. Install the updated version. 4. Restart the Traffic Server service. 5. Verify the version is updated.
🔧 Temporary Workarounds
Header Validation Filter
allImplement custom header validation to reject malformed Accept-Encoding headers before they reach Traffic Server.
# Configure web application firewall or reverse proxy to filter invalid Accept-Encoding headers
# Example regex pattern for validation: ^(gzip|deflate|br|identity|\*)(?:\s*,\s*(gzip|deflate|br|identity|\*))*$
🧯 If You Can't Patch
- Implement rate limiting on origin servers to prevent overload from cache bypass attacks.
- Deploy a web application firewall (WAF) in front of Traffic Server to filter malicious Accept-Encoding headers.
🔍 How to Verify
Check if Vulnerable:
Check the Traffic Server version using 'traffic_server -V' and compare against affected versions.Check Version:
traffic_server -VVerify Fix Applied:
After patching, verify version is 8.1.11 or higher for 8.x branch, or 9.2.5 or higher for 9.x branch.📡 Detection & Monitoring
Log Indicators:
- Unusual increase in cache misses
- Spike in requests to origin servers
- HTTP requests with malformed Accept-Encoding headers in access logs
Network Indicators:
- Increased traffic to origin servers
- Repeated requests for same resources with varying Accept-Encoding headers
SIEM Query:
source="traffic_server" AND ("cache miss" OR "forwarding") | stats count by src_ip