Fix for CWE-601: URL Redirection to Untrusted Site ('Open Redirect')

[asadeddin]

Corgea is an AI security engineer that fixes vulnerable code.

It issued this PR to fix a vulnerability for you to review.

See the issue and fix in Corgea.

Explanation of the issue

CWE-601: URL Redirection to Untrusted Site ('Open Redirect')
A web application accepts a user-controlled input that specifies a link to an external site, and uses that link in a Redirect. This simplifies phishing attacks.
An http parameter may contain a URL value and could cause the web application to redirect the request to the specified URL. By modifying the URL value to a malicious site, an attacker may successfully launch a phishing scam and steal user credentials. Because the server name in the modified link is identical to the original site, phishing attempts have a more trustworthy appearance. Whether this issue poses a vulnerability will be subject to the intended behavior of the application. For example, a search engine might intentionally provide redirects to arbitrary URLs.

Explanation of the fix

The fix involves using Django's is_safe_url function to validate the URL before redirecting, thus preventing open redirects to untrusted sites.

• The is_safe_url function from Django's http utilities is imported at the start of the file.
• Before the application redirects to the URL, it now checks if the URL is safe using the is_safe_url function. This function checks if the URL is a safe redirect target.
• The is_safe_url function takes two parameters: the URL to check and a set of allowed hosts. In this case, the allowed host is the host of the current request.
• If the URL is not safe, a ValidationError is raised with the message "Unsafe redirect detected." This prevents the application from redirecting to potentially malicious sites.
• This fix mitigates the risk of phishing attacks by ensuring that the application only redirects to URLs that are considered safe.