Apache Tomcat is one of the most widely used open-source web servers and servlet containers. Recently, a new vulnerability—CVE-2024-52316—was reported that could potentially allow users to bypass authentication under very specific conditions. While this vulnerability is subtle and requires a complex setup, understanding how it happens is important for any organization using Tomcat in production, especially with custom authentication modules.

Who is Affected?

This issue affects Apache Tomcat servers configured with a custom Jakarta Authentication (JASPIC) ServerAuthContext. If you haven't set up Tomcat with a custom authentication component, you're out of the risk zone, but it's *crucial* for anyone using advanced authentication setups.

What’s the Actual Problem?

The vulnerability arises if a developer builds a custom ServerAuthContext component for Tomcat using Jakarta Authentication (previously called JASPIC). If, during the authentication process, an exception gets thrown and the code does not set an HTTP status code to indicate failure, the authentication handler might not properly fail the request.

Here’s what happens

- Normal flow: If authentication fails, the HTTP response should have an explicit status like 401 (Unauthorized).
- Vulnerable flow: If authentication fails and throws an error without setting the status, Tomcat may just let the request through. This means users could get access to resources even though they haven’t authenticated correctly.

There are no known modules in the official ecosystem that behave this way out-of-the-box, but the risk lies in custom authentication logic.

Example: What Could Go Wrong?

Let's look at a simplified code example to illustrate the issue.

Suppose you write a custom JASPIC ServerAuthContext like this

public class MyAuthContext implements ServerAuthContext {
    @Override
    public AuthStatus validateRequest(MessageInfo messageInfo,
            Subject clientSubject, Subject serviceSubject) throws AuthException {
        HttpServletRequest request = (HttpServletRequest) messageInfo.getRequestMessage();
        try {
            // Custom authentication logic here
            if (!myCustomCredentialsCheck(request)) {
                throw new AuthException("Authentication failed");
            }
            return AuthStatus.SUCCESS;
        } catch (Exception e) {
            // This is the mistake: we just rethrow or swallow without setting an HTTP status.
            throw new AuthException(e.getMessage());
        }
    }
    
    // ... other methods ...
}

But we don't explicitly set the HTTP status code on the response object.

The risk: In some server flows, Tomcat might process the request as if authentication succeeded, because no "failure" signal was clearly given.

To fix this, always set the HTTP status code before returning or throwing

if (!myCustomCredentialsCheck(request)) {
    HttpServletResponse response = (HttpServletResponse) messageInfo.getResponseMessage();
    response.setStatus(HttpServletResponse.SC_UNAUTHORIZED); // 401
    return AuthStatus.SEND_FAILURE;
}

Or in a catch block

catch (Exception e) {
    HttpServletResponse response = (HttpServletResponse) messageInfo.getResponseMessage();
    response.setStatus(HttpServletResponse.SC_UNAUTHORIZED);
    return AuthStatus.SEND_FAILURE;
}

Exploit Details & Scenarios

Real-world impact?
There are no known publicly available Tomcat modules that act this way by default. However, if you or a third party wrote custom authentication code—and made the coding mistake above—an attacker could bypass authentication simply by triggering an error, such as a malformed authentication header.

How an exploit could look:
If an attacker knows the authentication flow will throw an exception (maybe by sending a purposely malformed request), and your implementation doesn’t set a failure status, they could sneak through to a protected resource.

But again, this only applies if you have custom ServerAuthContext logic that forgets to set HTTP status on error. Stock Tomcat and most third-party modules are not affected.

Audit Your Code:

- If you’ve created custom authentication handlers, make sure to set HTTP error status explicitly on failure. Don't rely only on exceptions!

More Details & References

- Apache Tomcat Security Advisory for CVE-2024-52316
- CVE Entry at MITRE
- Tomcat 11. Changelog
- Jakarta Authentication Spec

In Summary

CVE-2024-52316 is a rare, but significant, vulnerability affecting custom authentication modules on Tomcat. If you build your own handlers, make sure to set failure statuses explicitly—don’t let authentication errors pass through unchecked. The easiest and safest solution is to upgrade your Tomcat, and double-check your authentication code.

Stay secure. And always handle authentication failures with clear, explicit signals!

Timeline

Published on: 11/18/2024 12:15:18 UTC
Last modified on: 11/18/2024 17:11:17 UTC