Vulnerability report

Exploited in the wild Confirmed confidence In CISA KEV

CVE-2025-6543

ADC Denial of Service

NetScaler / ADC · affected before 47.46

Watch CVE-2025-6543 Browse KEV feed
Severity
CVSS 9.2 · Critical
Confidence
Confirmed
Exploit status
Exploited in the wild
EPSS
10.6%
First observed
—
Last observed
—

Decision summary

What security teams need to know first

Direct answers before the deeper technical record.

What it is

CVE-2025-6543 is an unauthenticated vulnerability affecting NetScaler ADC, Gateway. Memory overflow vulnerability leading to unintended control flow and Denial of Service in NetScaler ADC and NetScaler Gateway...

Is it exploited?

Yes. Previdian tracks this CVE as a known exploited vulnerability. Confidence is confirmed. Listed in CISA KEV. Also confirmed by third-party sources.

Who is affected?

NetScaler / ADC affected before 47.46.

What should we do?

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

Overview

ADC Denial of Service

Memory overflow vulnerability leading to unintended control flow and Denial of Service in NetScaler ADC and NetScaler Gateway when configured as Gateway (VPN virtual server, ICA Proxy, CVPN, RDP Proxy) OR AAA virtual server

NetScaler Affected
ADC
Before 47.46 Before 59.19 Before 37.236
NetScaler Affected
Gateway
Before 47.46 Before 59.19 Before 37.236
Published
25 Jun 2025
Exploitation Reported
01 Jun 2026
Attack vector
Remote
Complexity
High
Privileges
None
User interaction
None

Tags

cisa

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

CVE

Recorded 01 Jun 2026

A trusted third party reported exploitation.

Known exploited vulnerability sources

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

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Source Added
CVE First 2026-06-01 10:36 UTC
CISA 2026-06-02 14:07 UTC
Daily CyberSecurity 2026-06-06 02:20 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.

Observed signals

Request targets
User-Agents
Callback hosts
0
0
0

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

Scanner coverage

No scanner integrations recorded yet.

Virtual patch status

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

Learn about virtual patches →

No detection artifacts or sensor request patterns are available for this CVE yet.

Check back as sensor telemetry and scanner integrations are updated.

Risk and context

Severity, weaknesses, and research context

CVSS v4.0

9.2 Critical

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

CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:H/VI:H/VA:H/SC:L/SI:L/SA:L

EPSS

10.6%

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 CVSS Scores

CVSS v4.0 9.2 Critical

CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:H/VI:H/VA:H/SC:L/SI:L/SA:L

CVSS v3.1 9.8 Critical

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

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)...

Recent mention · Daily CyberSecurity

Emergency Patch Release Secures Apache HTTP Server Deployments Against Remote Attacks

Daily CyberSecurity · 09 Jun 2026

Multiple Memory Exploits Resolved in Major Version 2.4.68 Maintenance Cycle The development group managing the global web server The post Emergency Patch Release Secures Apache HTTP Server Deployments Against Remote Attacks appeared first on Daily CyberSecurity. Related posts: Urgent Citrix NetScaler Alert: Critical Memory Overflow Flaw (CVE-2025-6543, CVSS 9.2) Actively Exploited on 2,100+ Unpatched Appliances Apache bRPC Flaw (CVE-2025-54472) Allows Remote Denial-of-Service Attack Critical WordPress Plugin Flaw (CVE-2025-7384, CVSS 9.8) Exposes 70,000+ Sites to RCE and Data Loss

Recent mention · Daily CyberSecurity

Critical Sitefinity Vulnerabilities: CVSS 10.0 Security Alert

Daily CyberSecurity · 08 Jun 2026

Security Alert: Urgent Action Required for Progress Sitefinity Progress Sitefinity has issued a high-priority alert regarding several major The post Critical Sitefinity Vulnerabilities: CVSS 10.0 Security Alert appeared first on Daily CyberSecurity. Related posts: High-Severity Flaw in HashiCorp Nomad (CVE-2025-4922) Allows Privilege Escalation TeamViewer Remote Management Bug (CVE-2025-36537) Enables Privilege Escalation Urgent Citrix NetScaler Alert: Critical Memory Overflow Flaw (CVE-2025-6543, CVSS 9.2) Actively Exploited on 2,100+ Unpatched Appliances

Recent mention · Daily CyberSecurity

CISA Warns of Actively Exploited SolarWinds Serv-U Flaw

Daily CyberSecurity · 06 Jun 2026

Severe Infrastructure Exposure Discovered The Cybersecurity and Infrastructure Security Agency (CISA) recently added a new threat to its The post CISA Warns of Actively Exploited SolarWinds Serv-U Flaw appeared first on Daily CyberSecurity. Related posts: The ‘Must-Patch’ List: CISA Adds Actively Exploited SolarWinds, Ivanti, and Omnissa Flaws to KEV Urgent Citrix NetScaler Alert: Critical Memory Overflow Flaw (CVE-2025-6543, CVSS 9.2) Actively Exploited on 2,100+ Unpatched Appliances CISA Alert: Actively Exploited Zero-Days in CrushFTP, Chrome, and SysAid Added to KEV Catalog

Timeline

From disclosure to observed exploitation

  1. 10:21 UTC

    KEV confirmed by Tenable Blog

    Exploitation attested by an external source

  2. 02:20 UTC

    KEV confirmed by Daily CyberSecurity

    Exploitation attested by an external source

  3. 14:07 UTC

    Added to CISA KEV

    Listed in the CISA Known Exploited Vulnerabilities catalog

  4. 10:36 UTC

    Added to Previdian KEV Feed

    High-confidence, third-party attested exploitation

  5. 12:49 UTC

    CVE published

    Vulnerability disclosed publicly

  6. 18:08 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
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  • Automation-ready JSON delivery

GET /api/v2/pro/kevs/CVE-2025-6543

Free JSON includes basic KEV fields 
{
  "cve_id": "CVE-2025-6543",
  "confidence": "Confirmed",
  "cvss_score": 9.2,
  "cvss_estimated": false,
  "epss_score": 0.10562,
  "exploit_status": {
    "exploited_in_the_wild": true,
    "active_exploitation_observed": false
  },
  "sensor_telemetry": { "attempts": 0, "sensors": 0 }
}