CVE-2026-88771: Citrix NetScaler Improper Input Validation Vulnerability

In short

Citrix NetScaler has a weakness classified as improper input validation (CWE-20). CISA added it to its Known Exploited Vulnerabilities catalog on 2026-09-27. NVD lists CVSS 4.0 at 9.5 CRITICAL.

What it is

“Citrix NetScaler ADC and NetScaler Gateway contain an improper input validation vulnerability that could allow an unauthenticated attacker to execute arbitrary commands.” — CISA KEV, retrieved 2026-11-01

“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.” — NVD, retrieved 2026-11-01

Who is affected

Citrix NetScaler. NVD lists the following versions as affected:

• Citrix Netscaler Application Delivery Controller: from 13.1 inclusive, before 13.1-64.23
• Citrix Netscaler Application Delivery Controller: from 13.1 inclusive, before 13.1.37.279
• Citrix Netscaler Application Delivery Controller: from 14.1 inclusive, before 14.1-73.37
• Citrix Netscaler Application Delivery Controller: from 14.1-66.68 inclusive, through 14.1-73.37
• Citrix Netscaler Gateway: from 13.1 inclusive, before 13.1-64.23
• Citrix Netscaler Gateway: from 14.1 inclusive, before 14.1-73.37

Exploitation status

CISA KEV added: 2026-09-27. Known ransomware campaign use: Not reported by CISA. Due date CISA set for US federal civilian agencies: 2026-09-30.

Scores

NVD CVSS 4.0: 9.5 CRITICAL; 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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X; source 50a63c94-1ea7-4568-8c11-eb79e7c5a2b5.

EPSS by FIRST: 82.16%; percentile 99.66; score date 2026-10-31. EPSS estimates the probability of exploitation in the next 30 days.

CWE: CWE-20, CWE-119.

Timeline

CISA 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.” — CISA KEV

What to do

• Confirm whether you run Citrix NetScaler and which version.
• Apply the vendor update or mitigation in the advisory.
• Follow CISA’s required action.
• Review the vendor guidance on signs of compromise.
• Track the fix through completion.

References

• Vendor Advisory: https://support.citrix.com/support-home/kbsearch/article?articleNumber=CTX697096
• NVD detail
• CVE.org record
• CISA KEV catalog

Sources and dates

CISA Known Exploited Vulnerabilities Catalog, version 2026.10.30; retrieved 2026-11-01. CISA KEV data: CC0 1.0. No endorsement by CISA.

NVD retrieved: 2026-11-01. This product uses the NVD API but is not endorsed or certified by the NVD.

EPSS scores by FIRST; score date 2026-10-31.