CVE-2025-5777

Citrix NetScaler ADC and NetScaler Gateway contain an out-of-bounds read (CWE-125) caused by insufficient input validation, which can cause the appliance to read beyond the intended memory buffer (a memory overread). The flaw is only triggerable when the appliance is configured as a Gateway (VPN virtual server, ICA Proxy, CVPN, or RDP Proxy) or as an AAA virtual server, so attackers who can reach those services can potentially induce the overread and obtain sensitive memory contents. Such disclosure could aid follow-on compromise, for example by exposing session or authentication data, and CISA notes known ransomware use. Organizations running NetScaler ADC or NetScaler Gateway in the affected Gateway/AAA configurations are exposed. The vulnerability was added to CISA's Known Exploited Vulnerabilities catalog on 2025-07-10 with known ransomware use and an EPSS of 100% (100th percentile), indicating active exploitation, while no public PoC is known and a CVSS score has not yet been assigned.

What to do: Apply the fixed NetScaler ADC/Gateway builds per Citrix's security advisory (exact affected/fixed version ranges are not in the available data, so consult the bulletin); per CISA KEV, apply vendor mitigations, follow BOD 22-01 guidance for cloud services, or discontinue use if mitigations are unavailable. Inventory appliances for Gateway (VPN virtual server, ICA Proxy, CVPN, RDP Proxy) or AAA virtual server configurations, since unconfigured/other deployments are not triggerable. After patching, terminate active and idle VPN sessions and hunt for anomalous access, given the known ransomware exploitation and the information-disclosure nature of the flaw.