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CVE-2026-19489 – Denial of Service (Memory Overflow) – NetScaler ADC and NetScaler Gateway 14.1 / 13

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Summary

CVE-2026-19489 is a buffer overflow (CWE-120) affecting NetScaler ADC and NetScaler Gateway that can be triggered remotely without authentication when the appliance is configured with SIP ALG enabled on a Large Scale NAT (LSN) group. The flaw carries a CVSS score of 8.8 and can crash or destabilize the appliance, resulting in a denial-of-service condition. It was disclosed alongside a separate, more severe authentication bypass vulnerability (CVE-2026-19490) in the same Citrix security bulletin.

Technical details

  • Root cause: improper bounds checking when copying data into a buffer (CWE-120, classic buffer overflow) in the NetScaler packet-processing path.
  • Trigger condition: exploitation requires SIP ALG (Application Layer Gateway) to be enabled within an LSN group configuration on the appliance.
  • Attack vector: network, no authentication or privileges required, no user interaction needed.
  • Impact: unexpected appliance behavior and high impact to availability (per CVSS vector), consistent with a denial-of-service outcome; low confidentiality and integrity impact reported.

Affected software

  • NetScaler ADC: 14.1 through 14.1-73.32 (fixed in 14.1-73.32), 13.1 through 13.1-63.21 (fixed in 13.1-63.21)
  • NetScaler Gateway: 14.1 through 14.1-73.32, 13.1 through 13.1-63.21
  • Corresponding FIPS/NDcPP builds are also affected (fixed in 14.1-73.32 FIPS/NDcPP and 13.1-37.277 FIPS/NDcPP)
  • Secure Private Access Hybrid deployments that use NetScaler instances are also affected

Severity

  • CVSS score: 8.8 (High)
  • CVSS v4.0 vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:L/VI:L/VA:H/SC:N/SI:N/SA:L

Mitigation and recommended actions

  • Immediate: Upgrade NetScaler ADC and NetScaler Gateway to 14.1-73.32 or later, or 13.1-63.21 or later (or the corresponding FIPS/NDcPP builds), as published by Citrix (CTX696939).
  • If unable to patch immediately: Review LSN group configurations and disable SIP ALG where it is not required, since exploitation depends on this feature being enabled.
  • Ensure any NetScaler instances used for Secure Private Access Hybrid deployments are also upgraded to the fixed builds.

How IONIX identifies potentially affected assets

IONIX matches the following signals against data already collected when it crawled the asset; identifying the technology sends no request beyond that crawl.

  • set-cookie header: NSC_ (as a cookie name prefix), citrix_ns_id=
  • cookie header: NSC_ (as a cookie name prefix), citrix_ns_id=
  • content-security-policy header: nsgclient://, nsgcepa://
  • via header: NS-CACHE
  • URL path: /logon/LogonPoint/index.html (and variants matching that pattern)

References

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