CVE-2026-19490

Citrix NetScaler

score 90Known exploited · added 2026-09-09Public PoC ×2watchlist: citrix

Summary

Citrix NetScaler Authentication Bypass Using an Alternate Path or Channel Vulnerability

Citrix NetScaler ADC and NetScaler Gateway contain an authentication-bypass vulnerability involving an alternate path or channel. When the NetScaler appliance is configured as an AAA virtual server or as a Gateway (SSL VPN, ICA Proxy, CVPN, or RDP Proxy), an unauthenticated remote threat actor may be able to bypass authentication.

Published 2026-09-09 · first seen here 2026-10-10

CISA required action (due 2026-09-12): 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.

Analysis & write-ups

CVE-2026-19490 | Citrix NetScaler ADC and NetScaler Gateway Authentication Bypass Vulnerability · Horizon3.ai

Exploit availability

Public exploit code lowers the bar for attackers, so prioritise patching and hunting. These repositories are unverified. Fake PoCs that contain malware are common, so never run them outside an isolated lab.

TarPeg007/CVE-2026-19490 · ★17 · created 2026-09-02
BishopFox/CVE-2026-19490-check · ★1 · created 2026-09-10

Where it shows in your logs

CISA requires forensic triage for this CVE (BOD 26-04): check affected systems for signs of compromise, don't just patch.

Edge or network appliance (firewall, VPN, gateway) · Authentication bypass or missing authorisation high confidence

Appliances usually run no EDR, so device logs, firewall flow logs and the vendor's integrity checker are often the only evidence. Get the logs off the box: attackers often wipe local logs.

What to look for

Admin or API actions with no successful login before them in the same session
New admin accounts, API keys or tokens created shortly after unusual requests
Requests to admin or API endpoints from internet IPs
Configuration changes, new local admin accounts or new VPN users on the appliance
Admin or VPN logins from unfamiliar IPs, especially VPS or hosting providers
New outbound connections from the appliance's own IP (it should rarely start connections)
Gaps in the appliance's logs, unexpected reboots or crashes, or logs that were cleared

Data sources

Appliance system and admin logs · ATT&CK DS0015 Application Log Content

Sentinel: CommonSecurityLog (CEF from Fortinet, Palo Alto, Check Point, Cisco)Syslog
Splunk: Vendor add-ons: fortigate_event, pan:system, pan:config, cisco:asa, citrix:netscaler:syslog, f5:bigip:syslogChange.All_Changes
CrowdStrike: Falcon Next-Gen SIEM: third-party firewall / VPN connectors

Authentication and sessions · ATT&CK DS0028 Logon Session Creation / DS0002 User Account Authentication

Sentinel: SigninLogsSecurityEvent (4624, 4625, 4648)DeviceLogonEventsIdentityLogonEvents_Im_Authentication
Splunk: Authentication.Authenticationpan:globalprotectVPN sourcetypes
CrowdStrike: UserLogonUserLogonFailed2Falcon Identity Protection events

Network connections · ATT&CK DS0029 Network Connection Creation / Network Traffic Flow

Sentinel: DeviceNetworkEventsCommonSecurityLog (firewall)_Im_NetworkSession
Splunk: Network_Traffic.All_TrafficFirewall sourcetypes (pan:traffic, fortigate_traffic, cisco:asa)
CrowdStrike: NetworkConnectIP4NetworkReceiveAcceptIP4NetworkConnectIP6

Account and group changes · ATT&CK DS0002 User Account Creation / Modification

Sentinel: SecurityEvent (4720, 4728, 4732, 4756)AuditLogsIdentityDirectoryEvents
Splunk: Change.All_Changes (Account_Management)WinEventLog:Security (4720, 4732)
CrowdStrike: UserAccountCreatedUserAccountAddedToGroup

A generic baseline worked out from the product type and weakness (CWE-288), not a detection. Check table and field names against your environment. Hunt queries for Sigma, Splunk, Sentinel and CrowdStrike are coming.