CVE-2023-4967
📋 TL;DR
CVE-2023-4967 is a buffer overflow vulnerability in Citrix NetScaler ADC and Gateway that allows remote attackers to cause denial of service. It affects systems configured as VPN virtual servers, ICA/RDP proxies, or AAA virtual servers. Organizations using these Citrix products for remote access are at risk.
💻 Affected Systems
- Citrix NetScaler ADC
- Citrix NetScaler Gateway
📦 What is this software?
Netscaler Application Delivery Controller by Citrix
View all CVEs affecting Netscaler Application Delivery Controller →
Netscaler Application Delivery Controller by Citrix
View all CVEs affecting Netscaler Application Delivery Controller →
Netscaler Application Delivery Controller by Citrix
View all CVEs affecting Netscaler Application Delivery Controller →
Netscaler Application Delivery Controller by Citrix
View all CVEs affecting Netscaler Application Delivery Controller →
Netscaler Application Delivery Controller by Citrix
View all CVEs affecting Netscaler Application Delivery Controller →
⚠️ Risk & Real-World Impact
Worst Case
Complete service disruption of NetScaler ADC/Gateway, making VPN and remote access services unavailable to all users.
Likely Case
Service crashes leading to temporary unavailability of remote access services until manual restart.
If Mitigated
Limited impact with proper network segmentation and monitoring allowing quick detection and recovery.
🎯 Exploit Status
Buffer overflow vulnerabilities in network appliances often have low exploitation complexity once details are known.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: NetScaler ADC and NetScaler Gateway 14.1-12.35, 13.1-51.15, 13.0-92.21, 12.1-65.36
Vendor Advisory: https://support.citrix.com/article/CTX579459/
Restart Required: Yes
Instructions:
1. Download appropriate firmware version from Citrix downloads portal. 2. Backup current configuration. 3. Upload and apply firmware update via NetScaler GUI or CLI. 4. Reboot appliance after update completes.
🔧 Temporary Workarounds
Disable vulnerable configurations
allTemporarily disable Gateway (VPN virtual server, ICA Proxy, CVPN, RDP Proxy) or AAA Virtual Server configurations if not essential
nscli> disable vpn vserver <vserver_name>
nscli> disable authentication vserver <vserver_name>
🧯 If You Can't Patch
- Implement strict network access controls to limit traffic to NetScaler management interfaces
- Deploy network-based DoS protection and monitoring for abnormal traffic patterns
🔍 How to Verify
Check if Vulnerable:
Check NetScaler version via GUI (System > Network > System Information) or CLI (shell> nsroot@ns# show version)Check Version:
shell> nsroot@ns# show versionVerify Fix Applied:
Verify version is updated to patched version and confirm services are running normally📡 Detection & Monitoring
Log Indicators:
- Service crashes in /var/log/ns.log
- High memory usage alerts
- Unusual traffic patterns to Gateway services
Network Indicators:
- Sudden drop in VPN connections
- Increased malformed packet traffic to port 443
SIEM Query:
source="netscaler" AND (event="service_crash" OR event="high_memory")