CVE-2023-43804: Information Leakage in urllib3 via HTTP Redirects when a `Cookie` Header is Present

urllib3 is one of the most widely used HTTP client libraries for Python due to its simple and user-friendly design. However, a vulnerability has been identified in the library, and we'll discuss the details in this post. The issue is assigned the CVE identifier of CVE-2023-43804.

Description

The urllib3 library doesn't provide special treatment to the Cookie HTTP header or offer any helpers for managing cookies over HTTP. Thus, the responsibility of handling cookies lies with the user. However, urllib3 users could unknowingly leak information via HTTP redirects to a different origin if they don't explicitly disable redirects while specifying a Cookie header.

Patch Details

To resolve this issue, users are advised to upgrade to urllib3 version 1.26.17 or 2..5. These versions incorporate a patch addressing the vulnerability, so users will be protected against the information leakage issue.

Here are some resources for further reading on the vulnerability and recommended fixes

- CVE Information: https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2023-43804
- urllib3 GitHub Repository: https://github.com/urllib3/urllib3
- Changelog for urllib3: https://github.com/urllib3/urllib3/blob/main/CHANGES.rst

Exploit Details

Imagine a scenario where a user is not aware of the potential information leakage via HTTP redirects and uses urllib3 to send a request with a Cookie header. The user could unintentionally disclose sensitive data to an unintended recipient in such situations.

The following code snippet illustrates the vulnerable urllib3 usage

import urllib3

http = urllib3.PoolManager()

headers = {
    "Cookie": "SESSIONID=secret_session_id;"
}

response = http.request("GET", "http://example.com/redirect";, headers=headers)

In this example, when the requested URL responds with a redirect to a different origin, the Cookie header (with the session ID) is propagated to the redirected URL. This could potentially expose a user's sensitive data to external parties.

To mitigate this issue, users should either update urllib3 to the patched versions mentioned above or disable redirects explicitly. To disable redirects, set the redirect parameter to False in the request method:

response = http.request("GET", "http://example.com/redirect";, headers=headers, redirect=False)

With this change, users can prevent the potential information leakage and protect their sensitive data.

Conclusion

Always stay vigilant and keep your libraries up-to-date to safeguard against possible information leakage and other vulnerabilities. Ensure to update urllib3 to version 1.26.17 or 2..5 and properly handle redirects to avoid unintended disclosure of sensitive information.

Timeline

Published on: 10/04/2023 17:15:10 UTC
Last modified on: 11/03/2023 22:15:10 UTC