How to fix CVE-2026-88771: Citrix NetScaler (exploited in the wild)

Improper input validation vulnerability in Citrix NetScaler ADC and Citrix NetScaler Gateway. This issue affects ADC: before 14.1-73.37, before 13.1-64.23, before 14.1-73.37 FIPS, and before 13.1.37.279 FIPS and NDcPP; Gateway: before 14.1-73.37 and before 13.1-64.23 leading to an unauthenticated attacker to execute arbitrary commands.

• Severity: CRITICAL (CVSS 4.0 9.5, vector CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:H/VA:H/SC:H/SI:H/SA:H).
• Weakness: CWE-20, CWE-119.
• NVD published 2026-09-27, status Analyzed.

Anyone running Citrix NetScaler in the version ranges below. Internet-facing instances are the priority.

• citrix netscaler application delivery controller: from 13.1 up to (not including) 13.1-64.23.
• citrix netscaler application delivery controller: from 13.1 up to (not including) 13.1.37.279.
• citrix netscaler application delivery controller: from 14.1 up to (not including) 14.1-73.37.
• citrix netscaler gateway: from 13.1 up to (not including) 13.1-64.23.
• citrix netscaler gateway: from 14.1 up to (not including) 14.1-73.37.
• citrix netscaler application delivery controller: from 14.1-66.68 up to and including 14.1-73.37.

Version ranges come from the NVD CPE configuration. Confirm against the vendor advisory before you rely on them.

• Exploited in the wild: added to the CISA Known Exploited Vulnerabilities catalog on 2026-09-27; federal remediation due date 2026-09-30.
• Metasploit module: exploit/freebsd/http/citrix_netscaler_cve_2026_88771 (Citrix NetScaler Unauthenticated Login Log Command Injection (CVE-2026-88771)), disclosure date 2026-09-27.
• Public proof-of-concept code: 12 GitHub repositories from 11 accounts, the first on 2026-09-27.

• EPSS (probability of exploitation activity in the next 30 days): 5.11%, higher than 92% of all scored CVEs (as of 2026-10-24).
• CVERadar threat level: 64/100 (see methodology).
• Likely ATT&CK techniques: T1190 Exploit Public-Facing Application (inferred); T1203 Exploitation for Client Execution (inferred); T1059 Command and Scripting Interpreter (inferred).

1. Find every instance. List where Citrix NetScaler runs, including test, DR and forgotten internet-facing systems, and record the installed version.

   show ns version

2. Upgrade to a fixed release. citrix netscaler application delivery controller: 13.1-64.23 or later; citrix netscaler application delivery controller: 13.1.37.279 or later; citrix netscaler application delivery controller: 14.1-73.37 or later; citrix netscaler gateway: 13.1-64.23 or later. Get the build from the vendor advisory.
3. If you can't patch today, follow CISA's 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.
4. Verify the fix. Re-run the version check above on every instance and confirm it reports the fixed build (13.1-64.23 or later). Re-scan from outside if the service is exposed.
5. Hunt for signs of earlier compromise. If the system was exposed before you patched, assume it may have been hit and check the items below.
6. Rotate credentials stored on or used by the affected system if you cannot rule out compromise, and keep the logs you reviewed.

Detection hints

• T1190 Exploit Public-Facing Application: Review WAF, reverse-proxy and application logs for unusual requests to NetScaler (odd paths, oversized or encoded payloads, bursts of errors), going back to at least 2026-09-27.
• T1059 Command and Scripting Interpreter: Watch for the service process spawning shells or script interpreters.
• T1203 Exploitation for Client Execution: Exploitation of client or server software usually shows as crashes of the affected process followed by unexpected child processes; check EDR alerts for both.

Detection commands are generic starting points, not CVE-specific signatures. Use the indicators from the vendor advisory when it publishes them.

• NVD: CVE-2026-88771 nvd.nist.gov/vuln/detail/CVE-2026-88771
• CVE.org record www.cve.org/CVERecord?id=CVE-2026-88771
• Vendor link from CISA KEV community.citrix.com/techzone-blogs/110_security-updates/netscaler-adc
• Vendor link from CISA KEV support.citrix.com/support-home/kbsearch/article?articleNumber=CTX6970
• Vendor link from CISA KEV support.citrix.com/external/article/CTX694799/steps-to-take-if-netscal
• CISA KEV catalog www.cisa.gov/known-exploited-vulnerabilities-catalog
• FIRST EPSS (2026-10-24) api.first.org/data/v1/epss?cve=CVE-2026-88771