Vulnerability report

Active exploitation observed Confirmed confidence In CISA KEV

CVE-2023-4966

Unauthenticated sensitive information disclosure

Citrix / NetScaler ADC · affected before 8.50

Watch CVE-2023-4966 Browse KEV feed
Severity
CVSS 9.4 · Critical
Confidence
Confirmed
Exploit status
Observed in sensors
EPSS
100.0%
First observed
12 Jun 2026
Last observed
23 Oct 2026

Decision summary

What security teams need to know first

Direct answers before the deeper technical record.

What it is

CVE-2023-4966 is an unauthenticated Unauthenticated sensitive information disclosure affecting Citrix NetScaler ADC, NetScaler Gateway. Sensitive information disclosure in NetScaler ADC and NetScaler Gateway when...

Is it exploited?

Yes. Previdian sensors observed exploitation attempts with confirmed confidence. Listed in CISA KEV. Also confirmed by third-party sources.

Who is affected?

Citrix / NetScaler ADC affected before 8.50.

What should we do?

Patch immediately, validate internet-facing exposure, and monitor for matching requests.

Overview

Unauthenticated sensitive information disclosure

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.

Citrix Affected
NetScaler ADC
Before 8.50 Before 49.15 Before 92.19 Before 37.164 Before 55.300
Citrix Affected
NetScaler Gateway
Before 8.50 Before 49.15 Before 92.19
Published
10 Oct 2023
Exploitation Reported
18 Oct 2023
Attack vector
Remote
Complexity
Low
Privileges
None
User interaction
None

Tags

malware nuclei_scanner cisa ransomware

CVE References

Exploitation evidence

Why Previdian marks this CVE as exploited

Third-party attestation and first-party sensor observation are shown separately so teams can judge the evidence chain.

Exploited in the wild

CISA

Recorded 18 Oct 2023

A trusted third party reported exploitation.

Active exploitation observed

Previdian sensor

First observed 12 Jun 2026

Previdian first observed exploitation attempts targeting this vulnerability in our honeypot sensors.

Used in malware

CISA

Recorded 18 Oct 2023

Malware families have been linked to exploitation of this CVE.

Proof of concept available

GitHub

Recorded 24 Oct 2023

Public scanner or PoC coverage increases practical exploitability.

Known exploited vulnerability sources

Per-source evidence links for KEV attestations are available through the Previdian Pro API.

Learn about Pro API access
Source Added
CISA First 2023-10-18 00:00 UTC
The Shadowserver 2026-05-30 00:00 UTC
Tenable Blog 2026-06-02 14:20 UTC
Previdian Sensors 2026-07-07 07:59 UTC
CVE 2026-07-31 04:10 UTC

Operational indicators for this CVE are listed under Detection.

Sensor telemetry

First-party evidence of exploitation activity

Previdian sensors recorded exploitation attempts targeting this vulnerability. The cards and chart show volume, unique attackers, and daily activity.

68

Attempts observed

51

Unique attacker IPs

20

Attacker countries

AE · AU · BG · CA · CH · DE · ES · FI · GB · IN · JP · KZ · LU · NL · PL · PT · RO · SG · US · YE

11

Sensors observed

CVE-2023-4966 exploitation attempts over the last 90 days

Daily events observed by Previdian sensors

Updated 24 Oct 2026

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27 Jul 14 Aug 1 Sep 19 Sep 24 Oct

First observed 12 Jun 2026 · Last observed 23 Oct 2026

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Detection

Operational artifacts and observed signals

Make the evidence actionable in scanner, SOC, and edge-control workflows.

Observed signals

Request targets
User-Agents
Callback hosts
1
20
0

Request targets and User-Agents available in Pro. Callback host details available in Enterprise.

Virtual patch status

No Previdian virtual patch is currently available. Future rules ship for ModSecurity, Cloudflare, and AWS WAF.

Learn about virtual patches →

Attacker IP Indicators

Attacker IP indicators observed · available in Pro and Enterprise.

Sensor-derived attacker IP indicators are available to Pro and Enterprise accounts under Detection and through the Pro API.

Learn about Pro API access

Scanner Artifacts

Scanner and exploit-framework references linked to this CVE.

Scanner Reference Detected
Nuclei https://github.com/projectdiscovery/nuclei-templates/blob/main/http/cves/2023/CVE-2023-4966.yaml 25 Apr 2025

Risk and context

Severity, weaknesses, and research context

CVSS v3.1

9.4 Critical

Potential damage if exploited. Separate from whether attackers are using it.

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:L

EPSS

100.0%

Estimated chance of exploitation in the next 30 days. Previdian's warning comes from evidence, not this score.

Weaknesses

Improper Restriction of Operations within the Bounds of a Memory Buffer CWE-119

Recent mention · The Hacker News

China-Linked Hackers Exploited BeyondTrust Zero-Day to Take Over Remote Support Servers

Ravie LakshmananOct 16, 2026Zero-Day / Vulnerability The China-nexus cyber espionage group tracked as Armory Castle (previously UNC5221 or Warp Panda) exploited a newly disclosed security flaw in BeyondTrust Remote Support (formerly Bomgar) as a zero-day in late August 2026....

Read full advisory

All Mentions

Recent mention · The Hacker News

China-Linked Hackers Exploited BeyondTrust Zero-Day to Take Over Remote Support Servers

The Hacker News · 16 Oct 2026

Ravie LakshmananOct 16, 2026Zero-Day / Vulnerability The China-nexus cyber espionage group tracked as Armory Castle (previously UNC5221 or Warp Panda) exploited a newly disclosed security flaw in BeyondTrust Remote Support (formerly Bomgar) as a zero-day in late August 2026. The vulnerability, tracked as CVE-2026-102764 (CVSS score: 9.3), is a case of improper origin validation in an internal messaging component that could be exploited by a remote attacker to perform file operations on an affected appliance. "The vulnerability exists within internal components of Remote Support,"...

Recent mention · Tenable Blog

Frequently asked questions about reported Citrix NetScaler zero-day vulnerabilities

Tenable Blog · 27 Sep 2026

There are reportedly two unpatched zero-day Citrix NetScaler vulnerabilities capable of enabling remote code execution that have been actively exploited in the wild, with no patches available at this time.Key takeawaysReports indicate that there are two critical zero-day vulnerabilities in Citrix NetScaler.The reports originate from a pre-notification sent out ahead of public disclosure, so there are currently no specific details about these flaws and no patches available.This post will be updated as new information becomes available.BackgroundTenable's Research Special Operations (RSO)...

Recent mention · Tenable Blog

Inside the customer environment: Where threat actors, vulnerabilities, and exposed assets intersect

Tenable Blog · 27 May 2026

Tenable Research has developed a graph-based model linking 600+ threat groups to real-world customer exposures. It reveals which vulnerabilities sit at the intersection of severity, active exploitation, and organizational risk.Key takeawaysThe "patch everything" strategy is dead: Vulnerability prioritization based on exploitation risk offers a path forward. A directed graph model linking 600+ threat actors to vulnerabilities in 7,800 customer environments reveals that 68% of organizations carry at least one CVE previously exploited by a named adversary, and 321 tracked threat groups can...

Recent mention · Tenable Blog

Reducing Remediation Time Remains a Challenge: How Tenable Vulnerability Watch Can Help

Tenable Blog · 25 Apr 2025

Timely vulnerability remediation is an ongoing challenge for organizations as they struggle to prioritize the exposures that represent the greatest risk to their operations. Existing scoring systems are invaluable but can lack context. Here’s how Tenable’s Vulnerability Watch classification system can help.BackgroundOver the past six years working in Tenable’s research organization, I’ve watched known vulnerabilities and zero-day flaws plague organizations in the immediate aftermath of disclosure or even years afterwards. Following each blog post or threat report we’ve published, I kept...

Potential Proof of Concepts

These PoCs are unverified and could contain malware. Use at your own risk.

Citrix Bleed - Leaking Session Tokens

nuclei · Created Unknown

Timeline

From disclosure to observed exploitation

  1. 04:10 UTC

    KEV confirmed by CVE

    Exploitation attested by an external source

  2. 14:20 UTC

    Public PoC available

    Public proof-of-concept code published

  3. 00:33 UTC

    Indicators of compromise added (55)

    Indicators of compromise recorded

  4. 00:33 UTC

    Observed by Previdian sensors

    Evidence-backed exploitation signal

  5. 14:20 UTC

    KEV confirmed by Tenable Blog

    Exploitation attested by an external source

  6. 00:00 UTC

    KEV confirmed by The Shadowserver

    Exploitation attested by an external source

  7. 00:00 UTC

    Nuclei template available

    Scanner coverage available

  8. 00:00 UTC

    Added to CISA KEV

    Listed in the CISA Known Exploited Vulnerabilities catalog

  9. 00:00 UTC

    First public exploitation report

    Exploit observed in malware

  10. 13:12 UTC

    CVE published

    Vulnerability disclosed publicly

  11. 15:51 UTC

    CVE ID reserved

    Identifier reserved by the CNA

Pro API

Automate this intelligence

Confidence, exploit status, sensor telemetry, PoCs, scanner integrations, mentions, and tags are available programmatically for VM, SOC, and CTI workflows.

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  • Evidence confidence and provenance
  • First-party sensor telemetry
  • PoC and scanner references
  • Affected versions and enrichment
  • Automation-ready JSON delivery

GET /api/v2/pro/kevs/CVE-2023-4966

Sample API response 
{
  "cve_id": "CVE-2023-4966",
  "confidence": "Confirmed",
  "cvss_score": 9.4,
  "cvss_estimated": false,
  "epss_score": 0.99999,
  "exploit_status": {
    "exploited_in_the_wild": true,
    "active_exploitation_observed": true
  },
  "sensor_telemetry": { "attempts": 68, "sensors": 11 }
}