Critical NetScaler Vulnerability Exploited in Attacks

CISA has confirmed that threat actors are actively leveraging a critical authentication bypass flaw in Citrix NetScaler ADC and NetScaler Gateway appliances. Tracked as CVE-2026-19490 with a CVSS score of 9.3, this vulnerability affects devices configured as gateways or AAA virtual servers and allows remote exploitation without prior authentication. Although Citrix released a patch on August 19, CISA added the bug to its Known Exploited Vulnerabilities catalog this week, citing observed attacks since September 3.