Urgent Alert: NetScaler bug CVE-2026-3055 probed by attackers could leak sensitive data

Citrix NetScaler ADC and NetScaler Gateway appliances contain a buffer overflow (CWE-119) that leaks sensitive information from device memory when the appliance is configured as a Gateway (VPN virtual server, ICA Proxy, CVPN, or RDP Proxy) or as an AAA virtual server. A remote attacker who can reach such a configuration can trigger the overflow and read memory contents, harvesting sensitive data such as session tokens (a technique that enables session hijacking which can bypass multi-factor authentication). Any organization running an affected NetScaler ADC or Gateway appliance in these configurations is exposed, with appliances deployed as VPN or access gateways being the primary concern. Exploitation is confirmed in the wild: the flaw was added to CISA's KEV catalog on 2023-10-18 with known ransomware use and a 100% EPSS exploitation probability, although no public proof-of-concept is known at this time. Because tokens stolen from memory can remain valid even after patching, responders must terminate all active and persistent sessions as part of remediation.

Do: Upgrade affected appliances to the patched builds cited in Citrix's advisory, then immediately kill all active and persistent ICA/AAA sessions per the vendor instructions, since patching alone does not invalidate session tokens attackers may have already stolen. If patching is not immediately possible, discontinue use of the affected Gateway/AAA configurations as CISA directs. Given known ransomware abuse, also hunt for signs of exploitation such as logins from unexpected sources, anomalous session reuse, or suspicious mailbox changes, and reset credentials for potentially exposed accounts.

CVE-2026-3055 is an out-of-bounds read (CWE-125) in Citrix NetScaler ADC and NetScaler Gateway caused by insufficient input validation when the appliance is configured as a SAML Identity Provider (IDP). An unauthenticated remote attacker can trigger the flaw by sending crafted input to the SAML IDP functionality, causing the appliance to read beyond the bounds of allocated memory and potentially disclose sensitive information from it. The CVSS 4.0 base score of 9.3 (critical) reflects a network-vector flaw requiring no privileges or user interaction. Only organizations running NetScaler ADC or NetScaler Gateway appliances with SAML IDP configured are affected, according to the available data. The flaw was added to CISA's Known Exploited Vulnerabilities catalog on 2026-03-30, carries an 87.2% EPSS probability of exploitation within 30 days, has a public proof-of-concept, and headlines indicate active reconnaissance and exploitation against NetScaler deployments, including federal patch directives.

Do: Apply the patched NetScaler ADC and NetScaler Gateway releases from Citrix's advisory as soon as possible, prioritizing internet-facing appliances (exact fixed version numbers are not in this data; check the vendor bulletin). Determine whether SAML IDP is configured on your appliances and, if it is not needed, disable or unbind it as an interim mitigation while reviewing appliance logs for suspicious authentication or reconnaissance traffic. Federal agencies must follow the CISA required action and BOD 22-01 guidance, with CISA directing patching by the stated Thursday deadline.