CVE-2025-6543
Citrix NetScaler ADC and Gateway Buffer Overflow Vulnerability
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 status
CISA Known Exploited Vulnerabilities
Listed by CISA on 30 June 2025. US federal agencies were required to remediate it by 21 July 2025.
EPSS — exploitation probability
FIRST puts the probability of exploitation activity in the next 30 days at 10.4%, which is higher than 95.8% of all scored vulnerabilities. EPSS is a forecast of activity, not a measure of severity, and it is rescored daily.
CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Frequently asked questions
Is CVE-2025-6543 being exploited by ransomware groups?
No ransomware group in this database is currently recorded as exploiting CVE-2025-6543.
What does CVE-2025-6543 affect?
CVE-2025-6543 affects 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
How severe is CVE-2025-6543?
CVE-2025-6543 is rated CRITICAL with a CVSS base score of 9.8. EPSS puts the probability of exploitation in the next 30 days at 10.4%, higher than 95.8% of all scored vulnerabilities. It is listed in the CISA Known Exploited Vulnerabilities catalog, with a federal remediation deadline of 21 July 2025.
How should organisations respond to CVE-2025-6543?
Apply the vendor patch for Citrix NetScaler ADC and Gateway as the first priority, and treat any internet-facing instance as the most urgent. Because this vulnerability is associated with ransomware activity, also review whether the affected systems were reachable before patching, rather than assuming that patching alone closes the incident.