CVE-2021-31522
📋 TL;DR
This vulnerability in Apache Kylin allows remote attackers to execute arbitrary code by exploiting unsafe reflection through Class.forName() with user-controlled input. It affects all Apache Kylin versions up to 2.6.6, 3.1.2, and 4.0.0, enabling remote code execution on vulnerable systems.
💻 Affected Systems
- Apache Kylin
📦 What is this software?
Kylin by Apache
Kylin by Apache
Kylin by Apache
Kylin by Apache
Kylin by Apache
⚠️ Risk & Real-World Impact
Worst Case
Full system compromise with remote code execution leading to data theft, ransomware deployment, or complete system takeover.
Likely Case
Remote code execution allowing attackers to install backdoors, exfiltrate sensitive data, or pivot to other systems.
If Mitigated
Limited impact if proper network segmentation and least privilege access controls are implemented.
🎯 Exploit Status
Exploitation is straightforward with publicly available proof-of-concept code. No authentication required.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Apache Kylin 2.6.7, 3.1.3, 4.0.1 and later
Vendor Advisory: https://lists.apache.org/thread/hh5crx3yr701zd8wtpqo1mww2rlkvznw
Restart Required: Yes
Instructions:
1. Download patched version from Apache Kylin website. 2. Backup current installation. 3. Stop Kylin service. 4. Replace with patched version. 5. Restart Kylin service. 6. Verify functionality.
🔧 Temporary Workarounds
Network Access Restriction
linuxRestrict network access to Kylin instances using firewall rules.
iptables -A INPUT -p tcp --dport 7070 -s trusted_ip_range -j ACCEPT
iptables -A INPUT -p tcp --dport 7070 -j DROP
Application Layer Filtering
allImplement WAF rules to block malicious Class.forName() payloads.
🧯 If You Can't Patch
- Isolate Kylin instances in separate network segments with strict firewall rules
- Implement application-level input validation to reject suspicious class names
🔍 How to Verify
Check if Vulnerable:
Check Kylin version via web interface or configuration files. Versions 2.6.6 and earlier, 3.1.2 and earlier, or 4.0.0 are vulnerable.Check Version:
grep 'kylin.version' $KYLIN_HOME/conf/kylin.propertiesVerify Fix Applied:
Verify Kylin version is 2.6.7+, 3.1.3+, or 4.0.1+ and test that Class.forName() with user input is properly sanitized.📡 Detection & Monitoring
Log Indicators:
- Unusual Class.forName() calls in application logs
- Unexpected Java class loading patterns
- Suspicious user input containing class names
Network Indicators:
- HTTP requests with malicious class name parameters
- Unusual outbound connections from Kylin servers
SIEM Query:
source="kylin.logs" AND ("Class.forName" OR "java.lang.Class") AND NOT expected_class_names