Zero-day vulnerability in Citrix NetScaler Gateway

Buffer overflow
CVE-2025-6543

Vulnerability details

Advisory: SB2025062606 - Remote denial of service in NetScaler Gateway and NetScaler ADC

Vulnerable component: Citrix NetScaler Gateway

CVE-ID: CVE-2025-6543

CVSSv3 score: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H/E:H/RL:O/RC:C

CWE-ID: CWE-119 - Memory corruption

Description:

The vulnerability allows a remote attacker to perform a denial of service (DoS) attack.

The vulnerability exists due to a boundary error when handling incoming requests. A remote attacker can send specially crafted traffic to the server, trigger memory corruption and perform a denial of service (DoS) attack.

Successful exploitation of the vulnerability requires that NetScaler is configured as Gateway (VPN virtual server, ICA Proxy, CVPN, RDP Proxy) OR AAA virtual server.

Note, the vulnerability is being actively exploited in the wild. 

External links:

https://support.citrix.com/support-home/kbsearch/article?articleNumber=CTX694788

About zero-day vulnerabilities

Zero-day vulnerability is an undisclosed vulnerability in software that hackers can exploit to compromise computer programs, gain unauthorized access to sensitive data, penetrate networks, etc. We consider vulnerability a zero-day when there is no solution provided from software vendor and the vulnerability is being actively exploited by malicious actors.

Zero-day candidate is a potential zero-day vulnerability in software which might have been used in targeted attacks, however there is no evidence to support this suggestion.