In this detailed analysis of the CVE-2024-21723 vulnerability, we will discuss how inadequate parsing of URLs can result in an open redirect. An open redirect is a security flaw in web applications that allows an attacker to redirect users to a malicious website without their knowledge or consent. This issue can lead to phishing, malware infections, and the theft of sensitive information like login credentials and personal data.

This vulnerability exists primarily due to the insufficient validation of user-supplied URLs, which can lead to an open redirect situation. In this article, we'll take a look at a code snippet that demonstrates this vulnerability, links to the original references, and the exploit details.

Code Snippet

Consider the following PHP code snippet, which takes user input, appends it to a URL, and then redirects the user to that URL.

$user_input = $_GET['url'];
$redirect_url = "https://example.com/redirect.php?url="; . $user_input;
header("Location: " . $redirect_url);

This code is vulnerable to an open redirect attack, as it appends user input directly to the URL without properly validating or sanitizing the input.

Exploit Details

A potential attacker can craft a URL with an embedded open redirect vulnerability. By manipulating the url parameter, they can redirect users to a malicious website of their choice. Here's an example of a crafted URL that exploits the open redirect vulnerability:

https://vulnerablewebsite.com?url=https://maliciouswebsite.com

When a user clicks on this seemingly legitimate link, they will be redirected to the attacker's website bypassing any security mechanisms like SameSite attribute, X-Content-Type-Options, and Referrer-Policy.

For a deeper understanding of open redirects, please consult the following resources

1. OWASP Open Redirect Guide: https://owasp.org/www-community/attacks/Open_redirect
2. CWE-601: URL Redirection to Untrusted Site ('Open Redirect'): https://cwe.mitre.org/data/definitions/601.html
3. Open Redirect Cheat Sheet: https://cheatsheetseries.owasp.org/cheatsheets/Open_Redirect_Cheat_Sheet.html

Conclusion

To mitigate the CVE-2024-21723 open redirect vulnerability, developers should ensure that their applications validate and sanitize all user-supplied input, particularly when dealing with URL redirection. Developers should also adhere to secure coding guidelines, such as those provided by the OWASP, improve overall security posture, and reduce the risk of open redirects leading to phishing, malware infection, and data exfiltration.

Following best practices like whitelisting known-good URLs, using a strict referrer-policy, and implementing user-agent/browser security features like Content Security Policy (CSP) can go a long way in protecting your web applications from open redirect and other common web vulnerabilities.

Timeline

Published on: 02/29/2024 01:44:03 UTC
Last modified on: 02/29/2024 13:49:29 UTC