CVE-2026-3055
CVE-2026-3055 is a security flaw in Citrix NetScaler, the gateway companies use to let staff reach internal apps from outside. Attackers can corrupt memory in Citrix NetScaler, which they use to take it over. The US Cybersecurity and Infrastructure Security Agency (CISA) added it to its catalog of flaws known to be used in attacks on 30 Mar 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 66.59, 62.23 and 37.262.
Description
CISA calls it an out-of-bounds read in Citrix NetScaler. In its words: “Citrix NetScaler ADC (formerly Citrix ADC), NetScaler Gateway (formerly Citrix Gateway) and NetScaler ADC FIPS and NDcPP contain an out-of-bounds reads vulnerability when configured as a SAML IDP leading to memory overread.”[1]
The underlying weakness is out-of-bounds read (CWE-125), in MITRE’s list of common software weaknesses.[2]
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 | 66.59 |
| ADC | 62.23 |
| ADC | 37.262 |
| Gateway | 66.59 |
| Gateway | 62.23 |
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 30 Mar 2026, 7 days after it was made public. CISA lists a flaw only when it has reliable evidence of it being exploited, and gave US federal agencies until 2 Apr 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 91%. 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 per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable.”[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 66.59, 62.23 and 37.262), or not in use. CISA gave US government agencies until 2 Apr 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 91%.[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-2026-88771: improper input validation ·
- CVE-2026-19490: authentication bypass using an alternate path or channel ·
- 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 out-of-bounds read flaws
- CVE-2023-36424, Microsoft Windows: out-of-bounds read ·
- CVE-2025-5419, Chrome and other Chromium browsers: out-of-bounds read and write ·
- CVE-2024-53150, Linux Kernel: out-of-bounds read ·
- CVE-2025-24991, Microsoft Windows: NTFS out-of-bounds read ·
- CVE-2025-22226, VMware ESXi, Workstation, and Fusion: information disclosure ·
Every Citrix flaw on CISA’s list · Everything added in March 2026
References
- ^ Cybersecurity and Infrastructure Security Agency. “Citrix NetScaler Out-of-Bounds Read Vulnerability”. Known Exploited Vulnerabilities Catalog, added 30 Mar 2026.
- ^ National Institute of Standards and Technology. “CVE-2026-3055 Detail”. National Vulnerability Database, published 23 Mar 2026.
- ^ Citrix. Advisories and fixes: support.citrix.com, support.citrix.com.
- ^ FIRST. “Exploit Prediction Scoring System”. EPSS 0.915, percentile 99.8, 31 Oct 2026.
- CVE Program. “CVE-2026-3055”. 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.