CVE-2026-88771

Citrix · NetScaler · Citrix NetScaler Improper Input Validation Vulnerability

Verdict
Patch soon · actively exploited, reachable from the internet without credentials, and in the top half of CVEs by near-term exploitation probability

Added to CISA KEV 2026-09-27 · exploited in the wild for 2 days

How a test catches it

Test

List every input that crosses a trust boundary, and next to it every place its value is used: a query, a path, a command, a buffer, a response body. The test is the pair, not the field.

Passes when

Each input is bounded or escaped for the specific use it reaches. Validation that is present but not specific to the use - rejecting the wrong characters, or the right ones in the wrong place - is not a pass, and neither is a length check standing in for a format check.

What an attacker can reach How likely Time What CISA says to do Sources All 548

What an attacker can reach

CVSS 9.5 CRITICAL. The score is a summary; these three components are the part that decides whether something scanning the internet can use it.

Attack vector	networkreachable over the network, with no local access needed
Privileges required	noneneeds no credentials at all
User interaction	nonecan be triggered with nobody interacting with the page or request
Base 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
Weakness	CWE-20

This describes the vulnerability. It says nothing about whether your systems run it.

How likely

EPSS puts the probability of exploitation in the next 30 days at 0.0106, which places it in the top half of all tracked CVEs. The percentile is the more useful half: 0.18 in absolute terms sounds low until you know most of the internet-facing software in the world scores under that.

EPSS probability	0.0106
Percentile	0.633 — top half

Time

Added to KEV	2026-09-27
Days exploited	2
Federal remediation due	not set
Ransomware use	no known ransomware campaign use

What CISA says to do

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.

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.

Sources

CISA Known Exploited Vulnerabilities catalog — exploited status, dates, required action
NVD — CVSS vector, weakness, references
support.citrix.com/support-home/kbsearch/article?articleNumber=CTX697096
www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2026-
FIRST EPSS record — probability and percentile

This page describes the bug, not your estate. It cannot tell you whether you run it, or whether your own systems carry the same class of flaw. That question is what an assessment answers.

Web application penetration testing · API security testing · every service