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· 2 min read

Citrix Bleed Vulnerability: An Overview and Detection Recommendations


The Citrix Bleed vulnerability, known as CVE-2023-4966, is a critical threat affecting Citrix Netscaler Gateway and ADC products. These products are integral for load balancing, firewall implementation, VPNs, and user authentication. The vulnerability allows attackers to retrieve sensitive information and hijack user sessions by dumping a Citrix appliance memory after a simple HTTP request.


Citrix Bleed has been exploited as a zero-day since late October after a very simple to use POC exploit was released, with at least four threat groups actively using it. A patch was released by Citrix on October 10, 2023 but many systems worldwide havent been patched.

Detection Techniques

Key to detecting Citrix Bleed exploitation is monitoring Citrix ADC's Syslog logs, specifically the “TCPCONNSTAT” message under the “SSLVPN” function. Anomalies between “Client IP” and “Source” fields indicate potential exploitation.Post-exploitation activities include rapid environment enumeration, data exfiltration, and ransomware deployment. Various MITRE ATT&CK techniques are employed by attackers, such as Remote Desktop Protocol for lateral movement and exfiltration over web services.

Scale of the Threat

Approximately 20,000 Citrix devices are estimated to have had session tokens stolen. Around 18,000 ADC appliances are still publicly accessible, as per Shodan search results.

Mitigation Recommendations

Organizations are advised to update their Citrix Netscaler Gateway and ADC products to the latest versions. Critical updates include versions 14.1-8.50 and later, 13.1-49.15 and later, among others. NetScaler ADC and Gateway version 12.1, now EOL, require urgent upgrading.