Exploited CVEs / Citrix / CVE-2023-4966

CVE-2023-4966

Citrix NetScaler ADC and NetScaler Gateway Buffer Overflow Vulnerability. Exploitation in the wild is confirmed by CISA, not predicted, and the vulnerability is known to be used in ransomware campaigns. Federal agencies were required to remediate by 2023-11-08 (that deadline has passed); treat that date as the outer bound for your own environment. The fix is in the vendor advisory: Citrix Security Bulletins, linked below.

HighCISA KEVRansomware

Actively exploited Citrix NetScaler ADC and NetScaler Gateway vulnerability, High severity, CVSS 7.5. Added to the CISA KEV catalog 2023-10-18.

Senserva AI read on CVE-2023-4966CISA required actionOfficial fix for CVE-2023-4966Admin questions

Risk summary

CVSS base
7.5
EPSS exploit probability
100%
Severity
High
Added to KEV
2023-10-18
CISA due date
2023-11-08 (past due)
Patch immediately
Exploited in the wild and used in ransomware campaigns.
The fix ships from the vendor: Citrix Security Bulletins.
Do this now: Move this ahead of everything else in the queue, then verify the fix actually landed on every exposed device.

Updated July 26, 2026. Data refreshed on every build from MSRC, CISA KEV, and FIRST EPSS.

Senserva AI Opinion for CVE-2023-4966

Citrix NetScaler ADC and Gateway leak sensitive session information through this buffer overflow whenever the appliance is configured as a Gateway or AAA virtual server, and its 100% EPSS score plus confirmed ransomware use reflect months of mass exploitation. The nasty property of this class of bug is that stolen session material keeps working after the patch: attackers replay hijacked sessions to walk in as legitimate users. It is rated High Severity (CVSS 7.5) and has been on the KEV list since October 2023.

Do this: Patch NetScaler appliances and then kill all active and persistent sessions so stolen tokens cannot be replayed.

AI-generated from public data, 2026-07-07. Verify against the vendor advisory before acting.

Senserva AI Opinion and rich prompt for CVE-2023-4966

Copy this prompt into Claude, ChatGPT, or Copilot. The facts are included, sourced from this page.

Full tracking and change history for CVE-2023-4966

Published
2023-10-18
Last revised
2023-10-18
Changes tracked
1

Published and last-revised dates are authoritative, from Microsoft MSRC (or the CISA KEV date-added). Senserva additionally records day-to-day changes from 2026-07-07, refreshed several times a day; the change count reflects that forward-only tracking.

CISA required action

Federal (BOD 22-01) remediation due date: 2023-11-08 (past due).

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.

Official fix for CVE-2023-4966

The authoritative fix and affected-version list are published by the vendor. Find the NetScaler ADC and NetScaler Gateway advisory on Citrix Security Bulletins.

Citrix Security BulletinsCISA KEV entry

Common questions about CVE-2023-4966

Is CVE-2023-4966 actively exploited?

Yes. CVE-2023-4966 was added to the CISA Known Exploited Vulnerabilities (KEV) catalog on 2023-10-18, which means exploitation in the wild has been confirmed, not predicted. Its EPSS 30-day exploitation probability is 100%. CISA also reports it is known to be used in ransomware campaigns.

What is the CISA deadline and required action for CVE-2023-4966?

CISA set the federal (BOD 22-01) remediation due date at 2023-11-08, which has passed; treat any unremediated system as overdue. The verbatim required action: 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.

What fixes CVE-2023-4966?

The authoritative fix is in the vendor advisory: see Citrix Security Bulletins for the patched NetScaler ADC and NetScaler Gateway versions and any workarounds. KEV listing makes this a fix-first item: patch it ahead of higher-CVSS issues nobody is exploiting.

Can I ask my own AI about CVE-2023-4966?

Yes. This page includes a free, ready-to-paste AI prompt containing CVE-2023-4966's key facts: severity, CVSS, EPSS, the KEV date, the CISA due date, and the required action. Copy it into Claude, ChatGPT, or Copilot; the data is refreshed twice a day (5 AM and 3 PM US Central).

More exploited Citrix CVEs

The newest Citrix entries on the CISA KEV catalog:

CVE-2026-3055CVE-2025-7775CVE-2024-8069CVE-2024-8068CVE-2025-5777CVE-2025-6543CVE-2023-6549CVE-2023-6548

All Citrix exploited CVEs on one page: Citrix vulnerabilities actively exploited.

Authoritative references

CVE recordNVD detailCISA KEV catalogFIRST.org EPSS

Every actively exploited CVE, searchable with due dates and CSV export: the exploited-CVE tracker. The newest additions: exploited this week.

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Lexicon: the terms on this page
CVE
Common Vulnerabilities and Exposures. A unique ID for one publicly known vulnerability, such as CVE-2025-1234.
KB
Microsoft Knowledge Base article. The identifier for a specific Microsoft update.
KEV
CISA Known Exploited Vulnerabilities. CVEs confirmed exploited in the wild. Fix these first.
CVSS
Common Vulnerability Scoring System. A standardized Severity score from 0 to 10.
EPSS
Exploit Prediction Scoring System. The probability a CVE will be exploited in the next 30 days.
MSRC
Microsoft Security Response Center. Microsoft's Patch Tuesday advisories and KB-to-CVE mapping.
NVD
National Vulnerability Database (NIST). Authoritative CVE metadata and CVSS scores.
Ransomware
The vulnerability is linked to known ransomware activity.
Reference: Microsoft CVE and vulnerability management, the full CVE-to-patch lookup ranked by real-world risk, and the Microsoft patching guide, how Intune, Windows Autopatch, Defender, and Azure Update Manager fit together.
Data notice: this page, the feeds, and the API are provided as is, for informational purposes only, without warranty of any kind. Senserva, LLC does not guarantee the accuracy, completeness, or timeliness of third-party data (MSRC, NVD, CISA KEV, EPSS) and accepts no liability for actions taken based on it; verify against the authoritative vendor advisory before acting. Built daily with Senserva Trustworthy AI. All use of this data is subject to the Senserva EULA.