CVE-2021-38540
📋 TL;DR
CVE-2021-38540 is an authentication bypass vulnerability in Apache Airflow's variable import endpoint. Unauthenticated attackers can add or modify Airflow variables used in DAGs, potentially leading to denial of service, information disclosure, or remote code execution. This affects Apache Airflow versions 2.0.0 through 2.1.2.
💻 Affected Systems
- Apache Airflow
📦 What is this software?
Airflow by Apache
⚠️ Risk & Real-World Impact
Worst Case
Remote code execution through malicious variable injection leading to complete system compromise.
Likely Case
Denial of service or information disclosure through variable manipulation.
If Mitigated
No impact if proper authentication controls are in place.
🎯 Exploit Status
Simple HTTP requests to unprotected endpoint; exploit tools available in security community.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 2.1.3
Vendor Advisory: https://lists.apache.org/thread.html/rac2ed9118f64733e47b4f1e82ddc8c8020774698f13328ca742b03a2%40%3Cannounce.apache.org%3E
Restart Required: Yes
Instructions:
1. Backup your Airflow configuration and database. 2. Upgrade to Airflow 2.1.3 or later using pip: 'pip install --upgrade apache-airflow==2.1.3'. 3. Restart Airflow services. 4. Verify the fix by checking version and testing authentication.
🔧 Temporary Workarounds
Network Access Control
linuxRestrict network access to Airflow web server using firewall rules.
iptables -A INPUT -p tcp --dport 8080 -s trusted_ip_range -j ACCEPT
iptables -A INPUT -p tcp --dport 8080 -j DROP
Reverse Proxy Authentication
allPlace Airflow behind a reverse proxy with authentication enabled.
# Configure nginx/apache with authentication before Airflow
🧯 If You Can't Patch
- Implement strict network segmentation and firewall rules to limit access to Airflow web interface.
- Deploy a web application firewall (WAF) with rules to block unauthenticated requests to variable import endpoints.
🔍 How to Verify
Check if Vulnerable:
Check Airflow version and attempt unauthenticated POST request to /api/v1/variables/import endpoint.Check Version:
airflow versionVerify Fix Applied:
Verify version is 2.1.3+ and test that unauthenticated requests to variable import endpoint return 401/403.📡 Detection & Monitoring
Log Indicators:
- Unauthenticated POST requests to /api/v1/variables/import
- Unexpected variable modifications in Airflow logs
Network Indicators:
- HTTP POST to /api/v1/variables/import without authentication headers
- Unusual traffic patterns to Airflow web interface
SIEM Query:
source="airflow" AND (url_path="/api/v1/variables/import" AND NOT user!="*")🔗 References
- https://lists.apache.org/thread.html/rac2ed9118f64733e47b4f1e82ddc8c8020774698f13328ca742b03a2%40%3Cannounce.apache.org%3E
- https://lists.apache.org/thread.html/rb34c3dd1a815456355217eef34060789f771b6f77c3a3dec77de2064%40%3Cusers.airflow.apache.org%3E
- https://lists.apache.org/thread.html/rac2ed9118f64733e47b4f1e82ddc8c8020774698f13328ca742b03a2%40%3Cannounce.apache.org%3E
- https://lists.apache.org/thread.html/rb34c3dd1a815456355217eef34060789f771b6f77c3a3dec77de2064%40%3Cusers.airflow.apache.org%3E
