Number: AL26-024
Date: September 27, 2026
Update: October 3, 2026
Audience
This Alert is intended for IT professionals and managers.
Purpose
An Alert is used to raise awareness of a recently identified cyber threat that may impact cyber information assets, and to provide additional detection and mitigation advice to recipients. The Canadian Centre for Cyber Security ("Cyber Centre") is also available to provide additional assistance regarding the content of this Alert to recipients as requested.
Details
The Canadian Centre for Cyber Security (Cyber Centre) is aware of critical vulnerabilities affecting Citrix NetScaler ADC and NetScaler Gateway appliances. In response to the vendor security bulletin Footnote 1 and blog Footnote 2 released on September 27, 2026, the Cyber Centre is issuing this alert to raise awareness of the vulnerabilities and associated reports of active exploitation.
Tracked as CVE-2026-88771 Footnote 3, this vulnerability is an Improper Input Validation vulnerability (CWE-20) Footnote 4. The vulnerability may allow a remote, unauthenticated attacker to execute arbitrary code on a vulnerable NetScaler appliance. Successful exploitation could result in complete compromise of the appliance, unauthorized access to applications and services, credential theft, lateral movement, and further compromise of internal systems.
Tracked as CVE-2026-88772 Footnote 5, this vulnerability is a Buffer Overflow vulnerability (CWE-119) Footnote 6. Successful exploitation may allow arbitrary code execution, memory corruption, denial of service conditions, or other unintended behaviour on affected appliances.
Reports indicate that these vulnerabilities are being exploited and have been observed across multiple Citrix customer environments worldwide, although the full extent of this activity remains unknown at this time.
Beginning of Update 1
On October 2, 2026, Citrix published guidance Footnote 10 regarding a newly identified issue affecting NetScaler ADC and NetScaler Gateway deployments configured to use SAML authentication. According to Citrix, a remote attacker may be able to trigger system instability, resulting in denial-of-service conditions, repeated appliance reboots, and potentially further exploitation.
This issue is understood to be distinct from the vulnerabilities CVE-2026-88771 and CVE-2026-88772 described in the original alert.
The updates released to address CVE-2026-88771 and CVE-2026-88772 do not remediate this newly identified issue. Organizations using SAML authentication on NetScaler appliances should review their deployments, monitor for signs of abnormal activity, and follow the mitigation guidance provided by CitrixFootnote 10.
Additionally, organizations should be aware that patching alone may not fully remediate systems previously compromised through CVE-2026-88771 and/or CVE-2026-88772. If exploitation was successful, persistence mechanisms may remain on affected appliances even after the updates are applied. Organizations are strongly encouraged to run the NetScaler Console Indicators of Compromise (IOC) detection toolFootnote 11 to assess whether compromise has occurred and to contact Citrix for further instructions and remediation guidance.
End of Update 1
Suggested actions
Organizations should review the Citrix security bulletin Footnote 1 to determine whether their deployments are affected, prioritize remediation of Internet-facing systems, and investigate for signs of compromise, particularly where evidence of suspicious activity predates the release of vendor fixes
The Cyber Centre also recommends that organizations:
- contact Citrix or their authorized support provider as soon as possible to obtain the latest security guidance and patch availability information
- Preserve forensic evidence before shutting down, rebooting, patching, rebuilding, or otherwise modifying affected appliances, where feasible.
- Preserve appliance logs, remote syslog records, and NetScaler Console logs.
- Collect support bundles and other diagnostic information that may assist future investigations.
- Review running processes and active network connections for suspicious or unexplained activity.
- Examine startup scripts, scheduled tasks, web application directories, and crash dump locations for unauthorized modifications or indicators of persistence.
- Preserve suspicious files and configurations before changing or removing them.
- Correlate findings with firewall, DNS, authentication, endpoint, and other supporting telemetry sources.
- Investigate unexpected outbound connections, unusual administrative access, and suspicious activity on connected systems.
- Review the attached list of indicators of compromise and investigate to find matching patterns.
- Follow Citrix guidance for suspected compromises, including isolation of affected appliances and assessment of credential exposure Footnote 7.
- Conduct an organization-specific risk assessment based on the criticality of affected NetScaler deployments, any suspicious findings, and the limited information currently available.
- Where operationally feasible and justified by the organization's risk assessment, consider temporarily disabling or shutting down Internet-facing NetScaler appliances until vendor guidance and security updates become available; organizations should carefully weigh the cybersecurity risks of continued operation against the operational and business impacts of service disruption before taking this action.
- Prepare to reset credentials, invalidate active sessions, and replace certificates if compromise is suspected
- Be prepared to rebuild or replace compromised appliances from trusted software and known-good configurations.
Note: Organizations operating Common Criteria Footnote 8 evaluated configurations should review Citrix's advisory Footnote 1 and apply the recommended updates in accordance with their change management and certification requirements.
In addition, the Cyber Centre strongly recommends that organizations review and implement the Cyber Centre’s Top 10 IT Security Actions Footnote 9.
- Consolidate, monitor, and defend Internet gateways
- Patch operating systems and applications
- Harden operating systems and applications
- Isolate web-facing applications
Should activity matching the content of this alert be discovered, recipients are encouraged to report via My Cyber Portal, or email contact@cyber.gc.ca.