CVE-2026-19489 is a memory overflow vulnerability in Citrix NetScaler ADC and NetScaler Gateway, rated with a CVSS score of 8.8. It can lead to unpredictable behavior or denial-of-service (DoS) when Session Initiation Protocol Application Layer Gateway (SIP ALG) is enabled on a Large Scale NAT (LSN) group configuration. Citrix has released updates to mitigate this issue.