CVE-2021-22919
📋 TL;DR
This vulnerability in Citrix ADC, Gateway, and SD-WAN WANOP appliances allows attackers to consume all available disk space through resource exhaustion. Affected organizations include those using vulnerable Citrix networking products, potentially disrupting services and causing denial-of-service conditions.
💻 Affected Systems
- Citrix ADC
- Citrix Gateway
- Citrix SD-WAN WANOP Edition
📦 What is this software?
Application Delivery Controller Firmware by Citrix
View all CVEs affecting Application Delivery Controller Firmware →
Application Delivery Controller Firmware by Citrix
View all CVEs affecting Application Delivery Controller Firmware →
Application Delivery Controller Firmware by Citrix
View all CVEs affecting Application Delivery Controller Firmware →
Application Delivery Controller Firmware by Citrix
View all CVEs affecting Application Delivery Controller Firmware →
Gateway by Citrix
Gateway by Citrix
⚠️ Risk & Real-World Impact
Worst Case
Complete disk space exhaustion leading to system crashes, service unavailability, and potential data corruption or loss.
Likely Case
Degraded performance, service interruptions, and operational disruption requiring manual intervention to clear disk space.
If Mitigated
Minimal impact with proper monitoring and disk space management in place, though still requiring patching.
🎯 Exploit Status
CWE-770 indicates resource exhaustion vulnerability that typically requires minimal technical skill to exploit once details are known.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Multiple fixed versions - refer to Citrix advisory CTX319135 for specific version mappings
Vendor Advisory: https://support.citrix.com/article/CTX319135
Restart Required: Yes
Instructions:
1. Review Citrix advisory CTX319135. 2. Identify affected products and versions. 3. Download and apply appropriate patches from Citrix support portal. 4. Schedule maintenance window for restart. 5. Verify patch application and system functionality.
🔧 Temporary Workarounds
Disk Space Monitoring and Alerting
allImplement proactive monitoring of disk usage with alerts for high utilization
# Example for monitoring (customize for your environment)
# Check disk usage: df -h
# Set up monitoring thresholds in your monitoring system
Access Control Restrictions
linuxRestrict network access to vulnerable appliances using firewall rules
# Example firewall rule to restrict access
# iptables -A INPUT -p tcp --dport <citrix-port> -s <trusted-networks> -j ACCEPT
# iptables -A INPUT -p tcp --dport <citrix-port> -j DROP
🧯 If You Can't Patch
- Implement strict network segmentation and firewall rules to limit access to vulnerable appliances
- Deploy aggressive disk space monitoring with automated alerts and manual cleanup procedures
🔍 How to Verify
Check if Vulnerable:
Check appliance version against affected versions listed in Citrix advisory CTX319135Check Version:
show version (on Citrix appliance CLI) or check via management interfaceVerify Fix Applied:
Verify installed version matches or exceeds patched versions from advisory, then test disk exhaustion attempts📡 Detection & Monitoring
Log Indicators:
- Rapid disk space consumption alerts
- System log warnings about low disk space
- Performance degradation logs
Network Indicators:
- Unusual traffic patterns to Citrix appliance management interfaces
- Multiple connection attempts to vulnerable services
SIEM Query:
source="citrix_appliance" AND (disk_usage>90 OR "low disk space" OR "disk full")