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Actively exploitedKnown ransomware use

CVE-2023-4966 Citrix NetScaler ADC and NetScaler Gateway Buffer Overflow Vulnerability

Citrix NetScaler ADC and NetScaler Gateway contain a buffer overflow vulnerability that allows for sensitive information disclosure when configured as a Gateway (VPN virtual server, ICA Proxy, CVPN, RDP Proxy) or AAA virtual server.

From the CISA KEV catalogue version 2026.11.06, with Cybergen analysis. Updated 6 Nov 2026.

Our Assessment

Should You Worry?

Patch nowCybergen assessment
  • CISA confirmed exploitation in the wild and added it to the Known Exploited Vulnerabilities catalogue on 18 Oct 2023.
  • CISA lists it as known to be used in ransomware campaigns.
  • Rated Critical severity (CVSS 9.4, scored by Vendor).
  • This product type is often exposed to the internet, which is where attackers scan for it first.
  • Named in Cybergen threat actor reporting: LockBit.
  • It has been in the catalogue for 1,115 days. Systems still unpatched now have almost certainly been scanned for it.
The Vulnerability

What It Is

Sensitive information disclosure in NetScaler ADC and NetScaler Gateway when configured as a Gateway (VPN virtual server, ICA Proxy, CVPN, RDP Proxy) or AAA  virtual server.

Affected Versions

ProductVersions
Citrix NetScaler ADC14.1 to before 8.50
13.1 to before 49.15
13.0 to before 92.19
13.1-FIPS to before 37.164
12.1-FIPS to before 55.300
12.1-NDcPP to before 55.300
Citrix NetScaler Gateway14.1 to before 8.50
13.1 to before 49.15
13.0 to before 92.19

From the public CVE record, as supplied by the vendor. Always confirm against the vendor advisory.

From Watch to Action

What To Do Now

  1. 1

    Find it

    Search your asset inventory and external attack surface for Citrix NetScaler ADC and NetScaler Gateway. Include cloud images, appliances and anything a supplier runs for you.

    Attack Surface Management
  2. 2

    Fix it

    Apply mitigations and kill all active and persistent sessions per vendor instructions [https://www.netscaler.com/blog/news/cve-2023-4966-critical-security-update-now-available-for-netscaler-adc-and-netscaler-gateway/] OR discontinue use of the product if mitigations are unavailable.

    Vulnerability Management
  3. 3

    Hunt for compromise

    If an affected system was reachable before you patched, assume it may have been hit. Check logs, new accounts, web shells and outbound connections from the date of exposure.

    Incident Response
  4. 4

    Prove it is fixed

    Rescan or test the system after patching. Upgrades that fail silently and forgotten secondary instances are common.

    Penetration Testing

Vendor Advisories

Regulation

The Compliance Clock

Cyber EssentialsRated critical, so if it affects devices in your Cyber Essentials scope, the update must be installed within 14 days of the vendor releasing it.NIS2If exploitation causes a significant incident, essential and important entities owe their CSIRT an early warning within 24 hours and a notification within 72 hours.DORAFinancial entities must classify ICT incidents and send an initial notification for a major incident within strict deadlines, with exploited flaws a common cause.US federal (BOD 22-01)Federal civilian agencies had until 8 Nov 2023 to remediate. A sensible benchmark for everyone else.

General guidance, not legal advice. Your obligations depend on your sector, scope and jurisdiction.

Stay Ahead

More Exploited Citrix Flaws

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CVE-2026-88779Citrix NetScaler Improper Restriction of Operations within the Bounds of a Memory Buffer VulnerabilityAdded 4 Oct 2026CVE-2026-88772Citrix NetScaler Improper Restriction of Operations within the Bounds of a Memory Buffer VulnerabilityAdded 27 Sep 2026CVE-2026-88771Citrix NetScaler Improper Input Validation VulnerabilityAdded 27 Sep 2026CVE-2026-19490Citrix NetScaler Authentication Bypass Using an Alternate Path or Channel VulnerabilityAdded 9 Sep 2026CVE-2026-8452Citrix NetScaler ADC and NetScaler Gateway Improper Restriction of Operations within the Bounds of a Memory Buffer VulnerabilityAdded 26 Aug 2026CVE-2026-3055Citrix NetScaler Out-of-Bounds Read VulnerabilityAdded 30 Mar 2026

All 27 exploited Citrix vulnerabilities

Not Sure If You Are Exposed?

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Evidence

Sources

  1. CISA Known Exploited Vulnerabilities catalogue
  2. NVD: CVE-2023-4966
  3. CVE record: CVE-2023-4966
  4. FIRST EPSS
  5. netscaler.com/blog/news/cve-2023-4966-critical-security-update-now-available-for-netscaler-adc-and-n
  6. support.citrix.com/article/CTX579459
  7. packetstormsecurity.com/files/175323/Citrix-Bleed-Session-Token-Leakage-Proof-Of-Concept.html