Description of Problem
A vulnerability has been discovered in NetScaler ADC (formerly Citrix ADC) and NetScaler Gateway (formerly Citrix Gateway). Refer below for further details.

Affected Versions
The following supported versions of NetScaler ADC and NetScaler Gateway are affected by the vulnerabilities:

NetScaler ADC and NetScaler Gateway 14.1 BEFORE 14.1-47.46
NetScaler ADC and NetScaler Gateway 13.1 BEFORE 13.1-59.19
NetScaler ADC 13.1-FIPS and NDcPP BEFORE 13.1-37.236-FIPS and NDcPP

NetScaler ADC 12.1-FIPS is not affected by this vulnerability.

Additional Note: Secure Private Access on-prem or Secure Private Access Hybrid deployments using NetScaler instances are also affected by the vulnerabilities. Customers need to upgrade these NetScaler instances to the recommended NetScaler builds to address the vulnerabilities.

This bulletin only applies to customer-managed NetScaler ADC and NetScaler Gateway. Cloud Software Group upgrades the Citrix-managed cloud services and Citrix-managed Adaptive Authentication with the necessary software updates.

Details
NetScaler ADC and NetScaler Gateway contain the vulnerability mentioned below:

CVE-ID

Description Pre-conditions CWE CVSSv4
CVE-2025-6543

Memory 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

CWE-119 - Improper Restriction of Operations within the Bounds of a Memory Buffer

CVSS v4.0 Base Score: 9.2

(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)

What Customers Should Do
Exploits of CVE-2025-6543 on unmitigated appliances have been observed.

Cloud Software Group strongly urges affected customers of NetScaler ADC and NetScaler Gateway to install the relevant updated versions as soon as possible.

NetScaler ADC and NetScaler Gateway 14.1-47.46 and later releases
NetScaler ADC and NetScaler Gateway 13.1-59.19 and later releases of 13.1
NetScaler ADC 13.1-FIPS and 13.1-NDcPP 13.1-37.236 and later releases of 13.1-FIPS and 13.1-NDcPP. Customers should contact support - https://support.citrix.com/support-home/home to obtain the 13.1-FIPS and 13.1-NDcPP builds that address this issue.

Note: NetScaler ADC and NetScaler Gateway versions 12.1 and 13.0 are now End Of Life (EOL) and no longer supported. Customers are recommended to upgrade their appliances to one of the supported versions that address the vulnerabilities.

Exploit attempts for unpatched Citrix vulnerability, Author: Johannes Ullrich

This one is a privesc bug yielding SYSTEM privileges for any VDI user, which is actually a lot worse than it might initially sound since that’s SYSTEM privileges on the server that hosts all the applications and access is ‘by design’ - allowing an attacker to impersonate any user (including administrators) and monitor behaviour, connectivity.

Two bugs in Citrix technology are drawing serious attention this week from the Cybersecurity and Infrastructure Security Agency.

CISA says federal agencies much patch one of the vulnerabilities — tagged as CVE-2023-6548 — by January 24. It’s one of the rare times the cyber agency has put a remediation date of less than three weeks on a vulnerability.

CISA did not respond to requests for comment about why the remediation timeline was shorter than most.

The other bug — listed as CVE-2023-6548 — must be fixed by February 7. CISA’s alerts are aimed at federal agencies but often serve as general warnings for the public.

Several new vulnerabilities with critical severity scores are causing alarm among experts and cyber officials.

Zero-day bugs affecting products from Citrix and Apache have recently been added to the Cybersecurity and Infrastructure Security Agency’s (CISA) known exploited vulnerability (KEV) list.

Incident responders at the cybersecurity company Rapid7 warned of hackers connected to the HelloKitty ransomware exploiting a vulnerability affecting Apache ActiveMQ, classified as CVE-2023-46604. Apache ActiveMQ is a Java-language open source message broker that facilitates communication between servers.

Citrix warned admins today to secure all NetScaler ADC and Gateway appliances immediately against ongoing attacks exploiting the CVE-2023-4966 vulnerability.

It's time for another round Citrix Patch Diffing! Earlier this month Citrix released a security bulletin which mentioned "unauthenticated buffer-related vulnerabilities" and two CVEs. These issues affected Citrix NetScaler ADC and NetScaler Gateway.

A threat actor believed to be tied to the FIN8 hacking group exploits the CVE-2023-3519 remote code execution flaw to compromise unpatched Citrix NetScaler systems in domain-wide attacks.

Fox-IT (part of NCC Group) has uncovered a large-scale exploitation campaign of Citrix NetScalers in a joint effort with the Dutch Institute of Vulnerability Disclosure (DIVD). An adversary appears to have exploited CVE-2023-3519 in an automated fashion, placing webshells on vulnerable NetScalers to gain persistent access. The adversary can execute arbitrary commands with this webshell, even when a NetScaler is patched and/or rebooted. At the time of writing, more than 1900 NetScalers remain backdoored. Using the data supplied by Fox-IT, the Dutch Institute of Vulnerability Disclosure has notified victims.

An unauthenticated RCE flaw (CVE-2022-27518) is being leveraged by APT5 to compromise Citrix ADC deployments.

Learn about security updates for versions 12.1 (including FIPS and NDcPP) and 13.0 before 13.0-58.32 of Citrix ADC and Citrix Gateway and get fixes for both (security bulletin CTX474995).

At the start of 2022, CrowdStrike Intelligence and CrowdStrike Services investigated an incident in which PROPHET SPIDER exploited CVE-2021-22941 — a remote code execution (RCE) vulnerability impacting Citrix ShareFile Storage Zones Controller — to compromise a Microsoft Internet Information Services (IIS) web server. The adversary exploited the vulnerability to deploy a webshell that enabled the downloading of additional tools. This incident highlights how PROPHET SPIDER continues to evolve their tradecraft while continuing to exploit known web-server vulnerabilities.