Netscaler IP Archive – Deyda Consulting Blog

Checklist for NetScaler (Citrix ADC) CVE-2025-5777 & CVE-2025-6543

On June 17, 2025, Citrix published a security advisory for CVE-2025-5777, followed by CVE-2025-6543 on June 25, 2025. Both are classified as critical and are actively being exploited in the wild.

Threat Overview

CVE-2025-5777: Critical vulnerability due to improper input validation → leads to memory overread
CVE-2025-6543: Enables memory overflow, potentially resulting in DoS or arbitrary code execution → Exploits available !

⚠️ Important: Simply applying the firmware update is not enough. You must manually terminate all active ICA and PCoIP sessions after patching to ensure the vulnerability is fully mitigated.

Checklist for NetScaler (Citrix ADC) CVE-2023-4966

Citrix issued an alert (10/10/2023) about a critical vulnerability (CVE-2023-4966) in all NetScaler (Citrix ADC) & Gateway systems. Several working exploits have been published.

Please note that simply updating the systems is not enough. The connection tokens must also be reset.

Important ! There are no patches for NetScaler (Citrix ADC) version 12.1 or older. These systems have reached their EOL and will therefore no longer be equipped with the necessary fix. In this case please update to the latest 13.0, 13.1 or 14.1 version.

The vulnerability allows anonymous remote code execution and thus unauthenticated attackers to take over various machines with root privileges.

Checklist for NetScaler (Citrix ADC) CVE-2023-3519

Citrix issued an alert yesterday (07/18/2023) about a critical vulnerability (CVE-2023-3519) in all NetScaler (Citrix ADC) & Gateway systems. To date, no working exploits have been published.

Important ! There are no patches for NetScaler (Citrix ADC) version 12.1 or older. These systems have reached their EOL and will therefore no longer be equipped with the necessary fix. In this case please update to the latest 13.0 or 13.1 version.

The vulnerability allows anonymous remote code execution and thus unauthenticated attackers to take over various machines with root privileges.

As we hear from the Citrix community, more and more attacked systems are being found. The first exploits have also been available for purchase on the dark web for some time.

Citrix ADC 101 – Fundamentals

The following is a collection of basic information about Citrix ADC. From licensing, to the most important commands, to the update procedures that can be performed.

General Information

Here is some basic information about Citrix ADC.

Operating System and Architecture

Citrix ADC is based on the open source operating system FreeBSD. Unlike the very similar Linux, FreeBSD has a modular kernel and Citrix has taken advantage of this to modify FreeBSD’s Bash shell by removing the networking subsystem and replacing it with its own. The modifications were placed in a custom kernel module called NetScaler Core Packet Processing Engine (PPE).

Checklist for Citrix ADC CVE-2019-19781

Citrix has released a critical vulnerability warning (CVE-2019-19781) in all Citrix ADC & Gateway systems one week before Christmas. Several working exploits have been released since Jan. 10, 2020 and are available to everyone.

Important ! The fix from Citrix with the Responder Policy does not work on systems with version 12.1.51.16/51.19, 50.31 and older. If this version is in use, please update to the latest 12.1 version.

The exploits allow remote code to be executed anonymously, allowing unauthenticated attackers to take over the various machines with root privileges.

Tag: Netscaler IP