Vulnerability report

Trusted Third Party Report Confirmed Confidence In CISA KEV

CVE-2023-6549

NetScaler ADC Denial of Service

Cloud Software Group / NetScaler ADC · affected before 12.35

Watch CVE-2023-6549 Browse KEV feed
Severity
CVSS 8.2 · High
Confidence
Confirmed
Exploit status
Trusted Third Party Report
EPSS
57.6%
First observed
—
Last observed
—

Decision summary

What security teams need to know first

Direct answers before the deeper technical record.

What it is

CVE-2023-6549 is an unauthenticated vulnerability affecting Cloud Software Group NetScaler ADC.

Have exploitation attempts been observed?

Yes. Exploitation attempts have been reported for this vulnerability. Previdian lists it as a known exploited vulnerability. Listed in CISA KEV. Also reported by third-party sources. Confidence is confirmed.

Who is affected?

Cloud Software Group / NetScaler ADC, including affected before 12.35, affected before 51.15, and affected before 92.21.

What should we do?

Prioritize remediation. Validate affected assets and apply vendor fixes on an accelerated timeline.

Overview

NetScaler ADC Denial of Service

Improper Restriction of Operations within the Bounds of a Memory Buffer in NetScaler ADC and NetScaler Gateway allows Unauthenticated Denial of Service and Out-Of-Bounds Memory Read

Cloud Software Group Affected
NetScaler ADC
Before 12.35 Before 51.15 Before 92.21 Before 37.176 Before 55.302
Published
17 Jan 2024
Exploitation Attempts Reported
17 Jan 2024
Attack vector
Remote
Complexity
Low
Privileges
None
User interaction
None

Tags

nessus_scanner cisa nuclei_scanner

CVE References

Exploitation evidence

Evidence of exploitation attempts

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

Exploitation Attempts Observed in the Wild

CISA

Recorded 17 Jan 2024

A trusted third party reported exploitation attempts.

Proof of concept available

Nuclei Templates

Recorded 12 Jun 2026

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 2024-01-17 00:00 UTC
Tenable Blog 2026-09-27 10:21 UTC

Detection

Operational artifacts and observed signals

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

Virtual patch status

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

Learn about virtual patches →

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-2023-6549.yaml 01 Jun 2026
Nessus https://www.tenable.com/plugins/nessus/189070 02 Jun 2025

Risk and context

Severity, weaknesses, and research context

CVSS v3.1

8.2 High

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:N/I:L/A:H

EPSS

57.6%

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 · Tenable Blog

Frequently asked questions about reported Citrix NetScaler zero-day vulnerabilities

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...

Read full advisory

All Mentions

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)...

Potential Proof of Concepts

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

Citrix Netscaler ADC & Gateway - Out-Of-Bounds Memory Read

nuclei · Created Unknown

Timeline

From disclosure to observed exploitation attempts

  1. 10:21 UTC

    KEV confirmed by Tenable Blog

    Exploitation attempts reported by an external source

  2. 14:21 UTC

    Public PoC available

    Public proof-of-concept code published

  3. 15:34 UTC

    Nuclei template available

    Scanner coverage available

  4. 09:26 UTC

    Nessus plugin available

    Scanner coverage available

  5. 20:15 UTC

    CVE published

    Vulnerability disclosed publicly

  6. 00:00 UTC

    Added to CISA KEV

    Listed in the CISA Known Exploited Vulnerabilities catalog

  7. 11:01 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.

Start 14-day Pro trial Read API docs
  • 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-2023-6549

Sample API response 
{
  "cve_id": "CVE-2023-6549",
  "confidence": "Confirmed",
  "cvss_score": 8.2,
  "cvss_estimated": false,
  "epss_score": 0.57633,
  "exploit_status": {
    "exploited_in_the_wild": true,
    "active_exploitation_observed": false
  },
  "sensor_telemetry": { "attempts": 0, "sensors": 0 }
}