CISA Sets September 30 Deadline for Federal Agencies to Patch Actively Exploited Citrix NetScaler Zero-Days

CISA has ordered U.S. federal agencies to apply patches by September 30 for two actively exploited zero-day vulnerabilities in Citrix NetScaler ADC and NetScaler Gateway. The flaws, tracked as CVE-2026-88771 and CVE-2026-88772, enable unauthenticated remote code execution under default configurations and affect systems commonly exposed to the internet. CVE-2026-88771 allows remote code execution without authentication on NetScaler ADC and Gateway, while CVE-2026-88772 can trigger remote code execution or denial of service via a memory overflow when DTLS is enabled on VPN vServers. Citrix has released fixes for versions 14.1 and 13.1, including FIPS and NDcPP builds, with minimum required builds of 14.1-73.37 and 13.1-64.23. The advisory also covers six additional vulnerabilities from CVE-2026-88773 to CVE-2026-88778 involving HTTP request smuggling and TCP ISN prediction issues. Unsupported branches NetScaler 12.1 and 13.0 receive no patches, requiring immediate migration. Organizations are advised to inventory instances, check for compromise indicators before patching, and preserve forensic evidence.

HispasecSeptember 28, 2026Translated from Spanish

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The U.S. Cybersecurity and Infrastructure Security Agency (CISA) has set September 30 as the deadline for federal agencies to patch two actively exploited zero-day vulnerabilities in Citrix NetScaler products. The flaws, identified as CVE-2026-88771 and CVE-2026-88772, permit unauthenticated remote code execution under typical deployment conditions and target perimeter devices such as remote access gateways and application publishing services.

CVE-2026-88771 is particularly severe because it allows remote code execution without authentication on NetScaler ADC and NetScaler Gateway using default settings. No additional requirements or credentials are needed, leaving unpatched systems fully exposed to attackers. CVE-2026-88772 can result in either remote code execution or denial of service through a memory overflow triggered when DTLS is enabled on VPN vServers, a configuration that is active by default in many deployments.

Citrix has published updates for the 14.1 and 13.1 branches, including FIPS and NDcPP certified builds. Administrators must apply at minimum version 14.1-73.37 or 13.1-64.23 (or their certified equivalents). Deployments of Secure Private Access Hybrid that rely on NetScaler instances inherit the same risk and require the same remediation.

The security bulletin also addresses six additional vulnerabilities ranging from CVE-2026-88773 to CVE-2026-88778. These include HTTP request smuggling, policy bypass issues, and techniques related to TCP ISN prediction. For the TCP ISN case, Citrix provides a recommended configuration change to mitigate specific scenarios when the affected functionality is in use.

CISA advises organizations to look for signs of compromise before applying patches when feasible and to preserve forensic evidence if compromise is suspected. In environments with limited telemetry, reviewing logs in NetScaler Console and engaging specialized forensic analysis can help distinguish between simply closing the vulnerability and leaving a latent intrusion undetected.

Non-federal organizations should follow the same urgency: first inventory all NetScaler instances, prioritize those exposed to the internet, verify DTLS status on VPN vServers, and schedule maintenance windows with rollback plans. NetScaler 12.1 and 13.0 are no longer supported and will not receive patches, making immediate migration to supported branches the only viable option.

CISA NetScaler ADC NetScaler Gateway CVE-2026-88771 CVE-2026-88772 Citrix

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