CVE-2026-19489

CVE-2026-19489 is a vulnerability in Citrix NetScaler ADC and NetScaler Gateway classified as a classic buffer overflow (CWE-120), meaning input is copied into a buffer without adequate size checks; it was disclosed by Citrix alongside CVE-2026-19490, the authentication bypass receiving most of the headline attention. Per the CVSS 4.0 vector (AV:N/AC:L/AT:N/PR:N/UI:N), the flaw is reachable over the network by an unauthenticated remote attacker with no user interaction, though detailed trigger conditions are not spelled out in the CVE description. The scoring (VC:L/VI:L/VA:H, base 8.8 High) indicates the primary impact is to availability — likely crashes or denial of service on the appliance — with low confidentiality and integrity impact. All organizations running NetScaler ADC or NetScaler Gateway 14.1 releases through build 73.32, or 13.1 releases through build 63.21, fall within the affected ranges. There is no evidence of exploitation so far: the issue is not in CISA KEV, has no known public proof-of-concept, and EPSS estimates only a 0.4% probability of exploitation in the next 30 days (32nd percentile).

What to do: Upgrade affected NetScaler ADC and NetScaler Gateway deployments to the fixed builds identified in Citrix's advisory (see AL26-019 and CISA advisory AV26-833 Update 1); affected ranges are 14.1 through build 73.32 and 13.1 through build 63.21. Until patched, limit internet exposure of appliance interfaces and monitor Citrix channels for signs of exploitation. Also verify whether the same appliances are affected by the related CVE-2026-19490 authentication bypass fixed in the same advisory.