CVE-2021-27577
📋 TL;DR
Apache Traffic Server incorrectly handles URL fragments, allowing attackers to poison the cache by manipulating fragment identifiers. This 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, potentially serving malicious content to users.
💻 Affected Systems
- Apache Traffic Server
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Attackers poison cache with malicious content, leading to widespread distribution of malware, phishing pages, or defaced content to all users accessing the affected cache.
Likely Case
Cache poisoning results in users receiving incorrect or manipulated content, potentially causing service disruption, data integrity issues, or serving malicious scripts.
If Mitigated
Limited impact with proper cache validation and monitoring, potentially causing minor service disruptions but no data compromise.
🎯 Exploit Status
Exploitation requires sending specially crafted URLs but does not require authentication.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Apache Traffic Server 7.1.13, 8.1.2, 9.0.2 or later
Vendor Advisory: https://lists.apache.org/thread.html/ra1a41ff92a70d25bf576d7da2590575e8ff430393a3f4a0c34de4277%40%3Cusers.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. Install the updated version. 4. Restart the Traffic Server service. 5. Verify the version is updated.
🔧 Temporary Workarounds
Cache Validation Rules
allImplement strict cache validation rules to reject URLs with suspicious fragment handling.
Configure cache rules in remap.config or cache.config to validate URL fragments
🧯 If You Can't Patch
- Implement network segmentation to isolate Traffic Server instances from untrusted networks.
- Deploy web application firewall (WAF) rules to detect and block malicious URL fragment patterns.
🔍 How to Verify
Check if Vulnerable:
Check the Apache Traffic Server version using the version command and compare against affected ranges.Check Version:
traffic_server -VVerify Fix Applied:
Verify the installed version is 7.1.13, 8.1.2, 9.0.2 or later and test with crafted URLs to ensure cache poisoning is prevented.📡 Detection & Monitoring
Log Indicators:
- Unusual URL patterns with fragment identifiers in access logs
- Cache miss/hit anomalies for similar URLs with different fragments
Network Indicators:
- HTTP requests with manipulated fragment identifiers targeting Traffic Server
SIEM Query:
source="traffic_server" AND (url="*#*" OR fragment="*")🔗 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
