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Citrix urges customers to fix critical NetScaler authentication bypass (CVE-2026-19490)

Citrix patched a critical authentication bypass, CVE-2026-19490, in NetScaler Gateway and NetScaler ADC, urging customers to upgrade immediately.

Citrix has patched two flaws in NetScaler ADC and NetScaler Gateway. CVE-2026-19490 is a critical authentication bypass (CVSS v4.0 9.3) that works when the appliance is configured as an SSL VPN, ICA Proxy, CVPN, RDP Proxy Gateway or AAA virtual server, with additional conditions depending on firmware and SAML configuration. A second flaw, CVE-2026-19489 (CVSS 8.8), is a memory overflow that can cause denial of service when SIP ALG is enabled on LSN setups. Rapid7 had not observed exploitation as of August 19, 2026, but urged emergency patching; a signature-based mitigation is available via NetScaler Console.

Related CVEs

  • Remote Authentication Bypass in Citrix NetScaler ADC and NetScaler Gateway
    Citrix NetScaler ADC and NetScaler Gateway contain an authentication-bypass vulnerability (CWE-288, 'using an alternate path or channel') that an unauthenticated remote threat actor can exploit. The flaw is triggerable when the appliance is configured as an AAA virtual server or as a Gateway, including SSL VPN, ICA Proxy, CVPN, or RDP Proxy deployments, allowing the attacker to bypass authentication without valid credentials. A successful bypass could give an attacker access to VPN-protected or AAA-gated resources as an authenticated user; no CVSS score has been published yet. Organizations running affected NetScaler appliances in these configurations are exposed, and affected version ranges are not specified in the available data, so defenders should consult Citrix advisory AL26-019. The flaw was added to CISA's KEV on 2026-09-09, indicating exploitation in the wild; ransomware use is unknown, no public PoC is known, and EPSS assigns a 3.4% probability of exploitation within 30 days (88th percentile).
    · Citrix NetScaler ADC and NetScaler Gateway KEV PoC large
  • Unauthenticated Buffer Overflow in Citrix NetScaler ADC and NetScaler Gateway
    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).
    · Citrix NetScaler ADC (formerly Citrix ADC) 14.1 releases through build 73.32; 13.1 releases through build 63.21 · Citrix NetScaler Gateway (formerly Citrix Gateway) 14.1 releases through build 73.32; 13.1 releases through build 63.21mass

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