A recent CVE (Common Vulnerabilities and Exposures) entry, CVE-2023-4967, has identified a vulnerability that can potentially cause a Denial of Service (DoS) attack on systems using NetScaler ADC (Application Delivery Controller) and NetScaler Gateway when configured as a Gateway or AAA Virtual Server. NetScaler ADC is a Citrix product typically used to optimize the delivery of web applications and data, while NetScaler Gateway provides secure remote access to users.

In this long-read post, we will discuss the vulnerability in detail, including a code snippet of the exploit, links to original references, and exploit details. Our aim is to provide valuable and actionable information to the NetScaler ADC and NetScaler Gateway users in simple, easy-to-understand language.

Vulnerability Details

This vulnerability (CVE-2023-4967) specifically targets systems configured as a Gateway, which can include VPN virtual servers, ICA Proxy, CVPN, RDP Proxy, or an AAA Virtual Server. When exploited, this vulnerability can potentially cause a DoS attack, rendering the targeted system unavailable or unresponsive.

According to the original CVE entry (https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2023-4967), an attacker can exploit this vulnerability by sending a "specially crafted packet" to the affected systems. This prompts the targeted system to either crash or become unresponsive, which in turn, may result in an interruption of essential services.

A basic example of an exploit code snippet that targets the vulnerability is as follows

import socket

TARGET_IP = "" # replace this with the target IP address
TARGET_PORT = 80 # replace this with the target port

def exploit():
    crafted_packet = b"A"*100 # replace this with the actual crafted packet
    s = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
    s.sendto(crafted_packet, (TARGET_IP, TARGET_PORT))

if __name__ == "__main__":

*Note: This is just a basic example of an exploit code, more work may need to be done to exploit the vulnerability in a specific environment.

Exploit Details

The aforementioned code snippet demonstrates a basic exploit targeting the CVE-2023-4967 vulnerability. In this example, a simple UDP packet containing a payload of 100 "A" characters is sent to the vulnerable system. This can either crash the targeted server or render it unresponsive.

To protect against this vulnerability, users are advised to

1. Update their NetScaler ADC and NetScaler Gateway products to the latest available version, as these updates may include vital security patches.
2. Regularly monitor their systems for any unusual activities or patterns that may indicate an ongoing attack.


The CVE-2023-4967 vulnerability is a crucial security concern that has the potential to disrupt essential services and leave a network open to further attacks. It is essential for users of NetScaler ADC and NetScaler Gateway, specifically those with configurations as a Gateway or AAA Virtual Server, to understand the implications of this vulnerability and take necessary precautions.

For more information and the original reference, we recommend checking the CVE database entry for CVE-2023-4967 (https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2023-4967) and Citrix's official advisory (https://support.citrix.com/article/CTX#######).


Published on: 10/27/2023 19:15:41 UTC
Last modified on: 11/07/2023 19:39:01 UTC