Citrix NetScaler auth bypass flaw sees PoC released
NCSC-NL warns of a NetScaler ADC/Gateway auth bypass with public PoC and likely imminent exploitation, plus a related memory overflow flaw.
Sourceadvisories.ncsc.nl — open the original
What to check
- Applies to
- The 2 CVEs named below. Whether you run an affected version is not assessed: check the versions the source lists.
- Exploitation
- CISA lists CVE-2026-19490 as exploited in the wild.
Citrix has patched two vulnerabilities in NetScaler ADC and NetScaler Gateway. CVE-2026-19490 is an authentication bypass using an alternate path or channel (CVSS v4 9.3), allowing an attacker to circumvent normal authentication and gain unauthorized access. It affects devices configured as a Gateway (VPN virtual server, ICA Proxy, CVPN, RDP Proxy), an AAA virtual server, or as a SAML Identity Provider (the latter an uncommon configuration). Proof-of-concept code for this flaw is now publicly available, and NCSC-NL assesses it very likely that exploitation will occur in the short term.
CVE-2026-19489 is a memory overflow (improper restriction of operations within the bounds of a memory buffer, CVSS v4 8.8) affecting NetScaler ADC/Gateway when configured as a SIP ALG within a Large Scale NAT (LSN) group, which can cause unpredictable behavior or denial of service.
Citrix has released updates addressing both issues. Given the availability of PoC code for the authentication bypass and the high likelihood of imminent exploitation, NCSC-NL rated this advisory as high priority. Defenders running NetScaler ADC/Gateway in the affected configurations should prioritize patching immediately and review authentication logs for anomalous access via Gateway, AAA, or SAML IdP configurations.
Mentioned in this report
Source reporting: https://advisories.ncsc.nl/2026/ncsc-2026-0318.html
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