Citrix NetScaler ADC and Gateway Zero-day Vulnerabilities Exploited in Attacks (CVE-2026-88771 & CVE-2026-88772)

The Cybersecurity and Infrastructure Security Agency (CISA) has ordered agencies to secure their systems against two critical Citrix NetScaler vulnerabilities that have been exploited in attacks. CISA added CVE-2026-88771 and CVE-2026-88772 to its Known Exploited Vulnerabilities Catalog. CISA urged users to patch the vulnerabilities before September 30, 2026.

CVE-2026-88771

This is an improper input validation flaw that may allow an unauthenticated attacker to execute arbitrary commands on the target system.

CVE-2026-88772

This is a memory overflow vulnerability that may allow an attacker to achieve remote code execution or denial of service.

Steps to verify the prerequisites for the vulnerabilities

CVE-2026-88771

Prerequisite: All NetScaler ADC and NetScaler Gateway deployments (Default configuration / No additional feature required).

Instructions: All NetScaler ADC and NetScaler Gateway deployments are affected, including those deployed with the default configuration.

CVE-2026-88772

Prerequisite: DTLS configuration enabled on NetScaler ADC or NetScaler Gateway (Note: Enabled by default on VPN vServer).

Instructions: Users can determine whether their NetScaler deployment meets this precondition by inspecting the configuration for DTLS-enabled virtual servers. A NetScaler Gateway is vulnerable if DTLS is not explicitly disabled, and other virtual servers are vulnerable if configured with DTLS.

Relevant configuration patterns to check:

• add vpn vserver vpn1 SSL 10.0.0.0 443 -Listenpolicy NONE 

  This indicates that DTLS is not explicitly disabled; it is enabled by default.

• add vpn vserver vpn1 SSL 10.0.0.0 443 -dtls OFF -Listenpolicy NONE

  This indicates DTLS is explicitly disabled, so the precondition is not met.

• add vpn vserver vs1 DTLS 10.11.1.1 443

This indicates DTLS is enabled.

• add lb vserver vd_dtls DTLS 10.146.111.74 443 -persistenceType NONE -cltTimeout 120

This indicates DTLS is enabled.

Citrix also addressed the following vulnerabilities in the advisory:

• CVE-2026-88773 is an HTTP request smuggling vulnerability affecting systems with HTTP enabled. Successful exploitation allows threat actors to interfere with how the affected system interprets and processes HTTP requests.
• CVE-2026-88774 is a configuration vulnerability affecting policies that use HTTP URL-based expressions. Successful exploitation allows threat actors to bypass affected feature policies.
• CVE-2026-88775 is a memory buffer-bound vulnerability affecting systems configured as a Gateway or an authentication, authorization, and auditing (AAA) virtual server. Successful exploitation allows threat actors to cause unexpected system behavior or a DoS condition.
• CVE-2026-88776 is a memory buffer bounds vulnerability affecting systems configured with an Oracle load-balancing virtual server. Successful exploitation allows threat actors to cause unexpected system behavior or a DoS condition.
• CVE-2026-88777 is a memory buffer overflow vulnerability affecting systems that use specified non-HTTP Layer 7 protocol features. Successful exploitation allows threat actors to cause unexpected system behavior or a DoS condition.
• CVE-2026-88778 is a predictable value vulnerability affecting systems with TCP enabled. Successful exploitation allows threat actors to predict TCP Initial Sequence Numbers (ISNs) on affected connections.

Affected versions

• Citrix NetScaler ADC and Citrix NetScaler Gateway 14.1 BEFORE 14.1-73.37
• Citrix NetScaler ADC and Citrix NetScaler Gateway 13.1 BEFORE 13.1-64.23
• Citrix NetScaler ADC FIPS BEFORE 14.1-73.37 FIPS
• Citrix NetScaler ADC FIPS and NDcPP BEFORE 13.1-37.279

Mitigation

• Citrix NetScaler ADC and Citrix NetScaler Gateway 14.1-73.37 and later
• Citrix NetScaler ADC and Citrix NetScaler Gateway 13.1-64.23 and later releases of 13.1
• Citrix NetScaler ADC 14.1-FIPS 14.1-73.37 FIPS and later releases of 14.1-FIPS
• Citrix NetScaler ADC 13.1-FIPS and 13.1-NDcPP 13.1.37.279 and later releases of 13.1-FIPS and 13.1-NDcPP

Please refer to the Citrix Security Bulletin (CTX697096) for more information.

Qualys Detection

Qualys customers can scan their devices with QID 388834 to detect vulnerable assets.

Please continue to follow Qualys Threat Protection for more coverage of the latest vulnerabilities.

References
https://support.citrix.com/support-home/kbsearch/article?articleNumber=CTX697096