IRONSMITHINTEL
CRITICALCVSS9.8
|
Actively Exploited
|CISA KEV|CVE-2025-6543|Auth: none — unauthenticated|Reboot: required|Manual only

Citrix NetScaler ADC and Gateway Buffer Overflow Vulnerability (CVE-2025-6543)

Citrix NetScaler ADC and Gateway contain a buffer overflow vulnerability leading to unintended control flow and Denial of Service. NetScaler must be configured as Gateway (VPN virtual server, ICA Proxy, CVPN, RDP Proxy) OR AAA virtual server.

Published Jun 25, 2025 · Updated May 17, 2026
Why patchRisk explained in plain English
Worst-case scenarioIf unpatched

A remote attacker, without authentication, can achieve full data confidentiality loss, arbitrary modification of data, complete denial of service or system unavailability. Federal agencies are required to remediate by 2025-07-21 under CISA BOD 22-01.

How the attack worksNo clicks needed

This is a Buffer Overflow (CWE-119) vulnerability in Citrix NetScaler ADC and Gateway. 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 Exploitation requires remote network access, low attack complexity, no authentication required, and no user interaction required.

📧

Phishing link

→

🖼

Malicious file

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Server compromised

Am I affected?Quick check

Probably yes if any of these apply:

●Network Security Team
●Firewall Administrators
●IT Security
●Running netscaler application delivery controller: 13.1 ≤ v < 13.1-37.236, 13.1 ≤ v < 13.1-59.19, 14.1 ≤ v < 14.1-47.46; netscaler gateway: 13.1 ≤ v < 13.1-59.19, 14.1 ≤ v < 14.1-47.46
Real-world incidentsWhat we've seen

CISA added this CVE to the Known Exploited Vulnerabilities catalog on 2025-06-30 based on evidence of active exploitation in the wild. Federal agencies required to remediate by 2025-07-21.

How to patch

Manual remediation steps

1
Identify affected hosts: query inventory for network-security installs in scope.
2
Apply the vendor security update referenced in CVE-2025-6543's advisory. No specific KB/version is encoded yet — consult the linked MSRC/vendor URL.
3
Verify the fix per the vendor's published verification steps.
4
Document the remediation in your change ticket and re-scan with your vulnerability scanner to confirm closure.
PowerShell automationComing soon

No tested PowerShell script for this entry yet. We’re prioritising automation based on user demand.

References

↗ CVE-2025-6543↗ MSRC Advisory↗ NVD↗ Vendor Advisory