Remote Authentication Bypass in Citrix NetScaler ADC and NetScaler Gateway
CISA: Citrix NetScaler Authentication Bypass Using an Alternate Path or Channel Vulnerability
CVSS 4.0
9.3critical
EPSS
6%p92
Published
()
KEV added
AI analysis
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).
What to do: Prioritize applying vendor fixes or mitigations per Citrix advisory AL26-019 in line with CISA BOD 26-04, focusing first on internet-facing appliances configured as AAA virtual servers or Gateways (SSL VPN, ICA Proxy, CVPN, RDP Proxy). Until patched, restrict internet exposure and review VPN/AAA authentication logs for signs of unauthenticated access, following CISA's Forensics Triage Requirements if compromise is suspected.
Affected
Citrix NetScaler ADC and NetScaler Gateway
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Estimated exposure
largeon the order of 10,000-100,000 internet-exposed NetScaler ADC/Gateway appliances — Public internet scans of NetScaler Gateway/ADC endpoints and the product's prevalence as an enterprise edge VPN and load-balancing appliance support this range, though only appliances configured as AAA virtual servers or Gateways are…
Order-of-magnitude estimate by the model from install counts, market share and public scan data it knows; verify before quoting.
Description
Vulnerability in NetScaler ADC and NetScaler Gateway. This issue affects ADC: from 14.1 through 73.32 and from 13.1 through 63.21; Gateway: from 14.1 through 73.32 and from 13.1 through 63.21.
CISA Known Exploited Vulnerability
Affected
Citrix NetScaler
Required action
Apply mitigations in accordance with vendor instructions, ensuring compliance with CISA’s BOD 26-04 Prioritizing Security Updates Based on Risk (see URL in Notes) guidance and CISA’s “Forensics Triage Requirements” (see URL in Notes). Follow applicable BOD 26-04 guidance for cloud services or discontinue use of the product if mitigations are unavailable. Stakeholders are responsible for evaluating each asset's internet exposure and ensuring adherence to BOD 26-04 patching guidelines.
CISA added critical Citrix NetScaler flaw CVE-2026-19490 (CVSS 9.3) to its KEV catalog after confirming exploitation of gateway and AAA virtual servers in the wild.
CISA warned that threat actors are exploiting CVE-2026-19490, a critical-severity flaw (CVSS 9.3) affecting NetScaler ADC and NetScaler Gateway appliances configured as a gateway (SSL VPN, ICA Proxy, CVPN, RDP Proxy) or AAA virtual server. Citrix patched the bug on August 19, and Rapid7 warned it is remotely exploitable without authentication. Sensor data from Previdian shows exploitation ongoing since at least September 3, one day after a public exploit appeared on GitHub, with matching requests observed from three IPs across three countries. CISA added the flaw to its Known Exploited Vulnerabilities catalog, giving federal agencies three days to patch under BOD 26-04.
CISA adds actively exploited Cisco, Citrix, and Fortinet edge-device flaws to KEV catalog, ordering federal agencies to patch by September 12, 2026.
CISA added CVE-2026-20079 (Cisco Secure Firewall Management Center authentication bypass, CVSS 10.0), CVE-2026-19490 (Citrix NetScaler ADC/Gateway authentication bypass, CVSS 9.3), and CVE-2025-25249 (FortiOS heap buffer overflow, CVSS 7.3) to the Known Exploited Vulnerabilities catalog with a September 12, 2026 deadline for FCEB agencies. Cisco confirmed active exploitation of CVE-2026-20079 in August 2026, while Previdian honeypots logged 56 NetScaler exploitation attempts since September 3. SOCRadar attributes Fortinet exploitation to a financially motivated Russian-speaking actor deploying the PivotC2 Node.js RAT, infecting 178 of over 3,000 targeted IP addresses, mostly in the US.
CISA added actively exploited Cisco FMC, Chrome V8, Fortinet and Citrix NetScaler flaws to its KEV catalog, ordering federal patching by September 12.
CISA added four actively exploited vulnerabilities to its Known Exploited Vulnerabilities catalog. CVE-2026-20079 (CVSS 10.0) is an unauthenticated authentication bypass in Cisco Secure Firewall Management Center's web interface enabling script execution and potential root access. CVE-2026-87491 (CVSS 8.8) is an out-of-bounds write in Chrome's V8 engine — the seventh actively exploited Chrome zero-day of 2026 — fixed in Chrome 153.0.8010.36. CVE-2025-25249 (CVSS 8.1) is a heap-based buffer overflow in FortiOS/FortiSwitchManager's cw_acd daemon being exploited with the PivotC2 RAT, and CVE-2026-19490 (CVSS 9.3) is a NetScaler SAML HTTP-Redirect authentication bypass; federal agencies must patch by September 12, 2026.
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.
CISA adds exploited Citrix NetScaler authentication bypass CVE-2026-19490 to the KEV catalog; federal agencies must patch by September 12.
CISA added CVE-2026-19490, a CWE-288 authentication bypass affecting NetScaler ADC and Gateway deployments configured as AAA virtual servers or Gateway services (including SSL VPN, ICA Proxy, and RDP Proxy), to the Known Exploited Vulnerabilities catalog. Citrix released fixes on August 19, 2026; honeypots recorded 56 attack attempts between September 3 and 8 after a public PoC, though no confirmed production compromises have been reported. Affected builds include 14.1 before 14.1-73.32 and 13.1 before 13.1-63.21; newer installations require SAML IdP configuration to be exposed.
CISA added four actively exploited vulnerabilities—Fortinet buffer overflow, Citrix NetScaler and Cisco auth bypasses, and a Chromium V8 write—to the KEV Catalog.
CISA added CVE-2025-25249 (Fortinet heap-based buffer overflow), CVE-2026-19490 (Citrix NetScaler authentication bypass), CVE-2026-87491 (Google Chromium V8 out-of-bounds write), and CVE-2026-20079 (Cisco Firewall Management Center authentication bypass) to its Known Exploited Vulnerabilities Catalog based on evidence of active exploitation. Under Binding Operational Directive 26-04, Federal Civilian Executive Branch agencies must prioritize rapid remediation of these high-risk vulnerabilities on exposed assets and verify whether systems were compromised before patching. CISA encourages all organizations to adopt risk-based vulnerability management and prioritize KEV Catalog remediation.
Citrix patches critical NetScaler Gateway and AAA authentication bypass CVE-2026-19490 (CVSS 9.3) plus a SIP ALG memory overflow flaw; exploitation attempts observed.
Citrix fixed CVE-2026-19490 (CVSS 9.3), an authentication bypass affecting customer-managed NetScaler ADC and Gateway appliances configured as Gateway (SSL VPN, ICA Proxy, CVPN, RDP Proxy) or AAA virtual servers, and CVE-2026-19489 (CVSS 8.8), a memory overflow causing DoS when SIP ALG is enabled in Large Scale NAT groups. Updates are available in versions 14.1-73.32, 13.1-63.21, and corresponding FIPS/NDcPP builds, while Citrix-managed cloud services were already patched. The flaws were reported by Samarth Vashisht of JPMorgan Chase's penetration-testing team, and Previdian later observed 10 exploitation attempts against CVE-2026-19490 from six unique IP addresses in Australia, Germany, Japan, and the US, with no confirmed compromise.
CVE-2026-19490 is a critical unauthenticated authentication bypass in Citrix NetScaler ADC and Gateway, remotely exploitable without user interaction.
An advisory published August 19, 2026 describes CVE-2026-19490, a critical authentication bypass affecting Citrix NetScaler ADC and NetScaler Gateway. The flaw carries a CVSS v4.0 base score of 9.3 and is remotely exploitable by unauthenticated attackers over the network without user interaction or elevated privileges. NetScaler ADC and Gateway are widely deployed enterprise products positioned at or near the network perimeter, providing load balancing, SSL/TLS offloading, and secure remote access. The text does not state whether exploitation has been observed in the wild.
CISA added actively exploited NetScaler flaw CVE-2026-19490 to its KEV catalog; the Canadian Cyber Centre urges Citrix ADC and Gateway admins to patch.
The Canadian Centre for Cyber Security updated advisory AV26-833 covering Citrix NetScaler ADC and Gateway vulnerabilities in versions 13.1 (prior to 13.1-63.21) and 14.1 (prior to 14.1-73.32), plus FIPS builds. On September 9, 2026, CISA added CVE-2026-19490 to the Known Exploited Vulnerabilities catalog, indicating confirmed exploitation. The bulletin also references CVE-2026-19489 from the Citrix NetScaler ADC and Gateway Security Bulletin. Administrators should apply the fixed builds, including 13.1-37.277 and 14.1-73.32 for FIPS variants.
Canadian Cyber Centre alerts on Citrix NetScaler ADC/Gateway flaws CVE-2026-19490 (authentication bypass) and CVE-2026-19489 (buffer overflow), urging emergency patching.
The Canadian Centre for Cyber Security issued alert AL26-019 covering two Citrix NetScaler vulnerabilities disclosed in a vendor advisory on August 19, 2026. CVE-2026-19490 (CWE-288) allows a remote unauthenticated attacker to bypass authentication on appliances configured as a Gateway for SSL VPN, ICA Proxy, CVPN, RDP Proxy, or as an AAA virtual server. CVE-2026-19489 (CWE-120) is a classic buffer overflow that may cause memory overflow, unpredictable behavior, or denial-of-service conditions. Affected appliances are vulnerable when configured as a SAML IdP; fixed versions include 14.1-73.32, 13.1-63.21, and 13.1-37.277 for FIPS.
On 19 August 2026 Citrix published an advisory fixing two critical-severity issues in NetScaler ADC and NetScaler Gateway versions 14.1 before 14.1-73.32 and 13.1 before 13.1-63.21, plus FIPS/NDcPP builds. CVE-2026-19490 (CVSS 9.3) is an authentication bypass via alternate path, exploitable when the appliance is configured as a Gateway (SSL VPN, ICA Proxy, CVPN, RDP Proxy) or AAA virtual server, with a SAML action condition on newer builds. CVE-2026-19489 (CVSS 8.8) is a memory overflow causing unpredictable behaviour or denial of service, requiring SIP ALG enabled on a Large Scale NAT group. CERT-EU recommends applying updated builds as soon as possible.