CVE-2021-37149
📋 TL;DR
This CVE describes an improper input validation vulnerability in Apache Traffic Server's header parsing that allows attackers to smuggle HTTP requests. Attackers can bypass security controls and potentially access backend systems. Affected versions include Apache Traffic Server 8.0.0 to 8.1.2 and 9.0.0 to 9.1.0.
💻 Affected Systems
- Apache Traffic Server
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Attackers could bypass security controls, access restricted backend systems, perform cache poisoning, or conduct request smuggling attacks leading to data exposure or unauthorized actions.
Likely Case
HTTP request smuggling allowing attackers to bypass security controls, potentially accessing backend systems or performing cache poisoning attacks.
If Mitigated
Limited impact with proper network segmentation, WAF protection, and monitoring in place to detect anomalous traffic patterns.
🎯 Exploit Status
Exploitation requires crafting malicious HTTP requests but does not require authentication. The vulnerability is in header parsing which is fundamental to HTTP processing.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 8.1.3 and 9.1.1
Vendor Advisory: https://lists.apache.org/thread/k01797hyncx53659wr3o72s5cvkc3164
Restart Required: Yes
Instructions:
1. Download Apache Traffic Server 8.1.3 or 9.1.1 from the official Apache website. 2. Stop the Traffic Server service. 3. Backup configuration files. 4. Install the patched version. 5. Restore configuration files. 6. Start the Traffic Server service.
🔧 Temporary Workarounds
Implement WAF rules
allConfigure Web Application Firewall to detect and block malformed HTTP headers and request smuggling attempts
Network segmentation
allIsolate Apache Traffic Server instances from critical backend systems to limit potential damage from successful exploitation
🧯 If You Can't Patch
- Implement strict network segmentation to isolate Apache Traffic Server from critical backend systems
- Deploy a Web Application Firewall (WAF) with rules specifically targeting HTTP request smuggling and malformed headers
🔍 How to Verify
Check if Vulnerable:
Check the Apache Traffic Server version using 'traffic_server -v' or examine the server binary/package versionCheck Version:
traffic_server -vVerify Fix Applied:
Verify the installed version is 8.1.3 or higher for the 8.x branch, or 9.1.1 or higher for the 9.x branch📡 Detection & Monitoring
Log Indicators:
- Unusual HTTP request patterns
- Malformed headers in requests
- Requests with unusual header sequences
- Failed request parsing attempts
Network Indicators:
- HTTP traffic with malformed or unusual headers
- Request smuggling patterns
- Traffic bypassing expected security controls
SIEM Query:
source="apache_traffic_server" AND (http_request contains "malformed" OR http_header contains "smuggle" OR http_error contains "parsing")