CVE-2026-88771
CVE-2026-88771 is a security flaw in Citrix NetScaler, the gateway companies use to let staff reach internal apps from outside. Attackers can run commands on Citrix NetScaler from anywhere, without logging in. The US Cybersecurity and Infrastructure Security Agency (CISA) added it to its catalog of flaws known to be used in attacks on 27 Sep 2026.[1]
Citrix NetScaler is business software or equipment. Most families won’t have it, but attackers break into it to get inside companies, and from there to what those companies hold about their customers, patients and staff. Fixed in version 14.1-73.37, 13.1-64.23, 14.1-73.37 FIPS and 13.1.37.279 FIPS and NDcPP.
Description
CISA calls it an improper input validation in Citrix NetScaler. In its words: “Citrix NetScaler ADC and NetScaler Gateway contain an improper input validation vulnerability that could allow an unauthenticated attacker to execute arbitrary commands.”[1]
The CVE record adds: “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.”[2]
The underlying weakness is memory buffer error (CWE-119), in MITRE’s list of common software weaknesses.
It scores 9.8 out of 10 on the Common Vulnerability Scoring System, which rates it critical, scored by NVD using CVSS 3.1.[2]
Affected versions
NVD’s record lists these fixed versions: in each line, everything before the version shown is affected.[2]
| Product | Fixed in |
|---|---|
| ADC | 14.1-73.37 |
| ADC | 13.1-64.23 |
| ADC | 14.1-73.37 FIPS |
| ADC | 13.1.37.279 FIPS and NDcPP |
| Gateway | 14.1-73.37 |
| Gateway | 13.1-64.23 |
Most families won’t have Citrix NetScaler; it’s for whoever looks after IT at work.
Exploitation
CISA added it to its catalog of known exploited vulnerabilities on 27 Sep 2026, within a day of it being made public. CISA lists a flaw only when it has reliable evidence of it being exploited, and gave US federal agencies until 30 Sep 2026 to fix it.[1]
FIRST’s Exploit Prediction Scoring System, which estimates how likely a flaw is to be used in attacks in the next 30 days from what it sees across the internet, puts it at 82%. That’s in the top 1% of the flaws it scores.[4]
CISA assesses it as automatable: attackers can run it against many targets at once.
CISA doesn’t say who was attacked, or how.
Fix
Citrix has published a fix or advice.[3] 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).”[1]
- Check whether you use it.Citrix NetScaler is business software or equipment, so most families won’t have it. If you run a business, or work from home on company equipment, ask whoever looks after your IT.
- Send this page to your IT person.Ask them to confirm it’s fixed (fixed in version 14.1-73.37, 13.1-64.23, 14.1-73.37 FIPS and 13.1.37.279 FIPS and NDcPP), or not in use. CISA gave US government agencies until 30 Sep 2026 to fix it.
- If it can’t be fixed, take it offline.CISA’s advice when there’s no fix is to stop using the product, or take it off the internet, until there is one.
You can’t fix someone else’s server, but you can watch for what follows a break-in like this: a breach notice, a password reset you didn’t ask for, or a scam message that knows things it shouldn’t. HARD watches for those for you and your family.
Timeline
| Date | Event |
|---|---|
| The flaw is made public in the National Vulnerability Database, with a severity score of 9.8.[2] | |
| CISA adds it to its catalog of flaws known to be used in attacks.[1] | |
| CISA’s deadline for US government agencies to fix it.[1] | |
| FIRST puts the odds of it being used in attacks in the next 30 days at 82%.[4] |
See also
Other Citrix NetScaler flaws
- CVE-2026-88779: improper restriction of operations within the bounds of a memory buffer ·
- CVE-2026-88772: improper restriction of operations within the bounds of a memory buffer ·
- CVE-2026-19490: authentication bypass using an alternate path or channel ·
- CVE-2026-3055: out-of-bounds read ·
- CVE-2025-7775: memory overflow ·
Other Citrix flaws
- CVE-2026-8452, Citrix NetScaler ADC and NetScaler Gateway: improper restriction of operations within the bounds of a memory buffer ·
- CVE-2024-8069, Citrix Session Recording: deserialization of untrusted data ·
- CVE-2024-8068, Citrix Session Recording: improper privilege management ·
- CVE-2025-5777, Citrix NetScaler ADC and Gateway: out-of-bounds read ·
- CVE-2025-6543, Citrix NetScaler ADC and Gateway: buffer overflow ·
Other memory buffer error flaws
- CVE-2009-3459, Adobe Acrobat and Reader: heap-based buffer overflow ·
- CVE-2025-31277, Apple devices: buffer overflow ·
- CVE-2026-3910, Chrome and other Chromium browsers: improper restriction of operations within the bounds of a memory buffer ·
- CVE-2008-0015, Microsoft Windows: video activeX control remote code execution ·
- CVE-2026-20700, Apple devices: multiple buffer overflow ·
Added the same day
- CVE-2026-88772, Citrix NetScaler: improper restriction of operations within the bounds of a memory buffer ·
Every Citrix flaw on CISA’s list · Everything added in September 2026
References
- ^ Cybersecurity and Infrastructure Security Agency. “Citrix NetScaler Improper Input Validation Vulnerability”. Known Exploited Vulnerabilities Catalog, added 27 Sep 2026.
- ^ National Institute of Standards and Technology. “CVE-2026-88771 Detail”. National Vulnerability Database, published 27 Sep 2026.
- ^ Citrix. Advisories and fixes: community.citrix.com, support.citrix.com, support.citrix.com.
- ^ FIRST. “Exploit Prediction Scoring System”. EPSS 0.822, percentile 99.7, 31 Oct 2026.
- CVE Program. “CVE-2026-88771”. The official CVE record.
This article is built from CISA’s catalog (version 2026.10.30), NVD’s record and FIRST’s scores, kept in HARD’s database and checked every morning. The plain English is HARD’s.