Apache Tomcat is a widely-used web server and servlet container, running everywhere from small businesses to huge enterprise data centers. A newly disclosed vulnerability—CVE-2024-52318—poses a risk to many Tomcat deployments, specifically versions 11.., 10.1.31, and 9..96. In this long read, we’ll explain what this flaw is, how someone might exploit it, and—most importantly—how to stay safe.

What Is CVE-2024-52318?

CVE-2024-52318 is a vulnerability categorized as incorrect object recycling and reuse inside Apache Tomcat. In plain language: when web servers handle HTTP requests, they often reuse certain Java objects (like objects representing HTTP requests or responses) to save memory and run faster. But in some Tomcat versions, the recycling process wasn’t done correctly. Objects might still hold data from previous requests when they are handed off to the next user.

Imagine you order food in a restaurant, and the server sometimes brings out a plate that wasn’t washed properly and still has leftovers from the last customer. That’s the digital version of what happened here—with much more dangerous implications.

Why Is This Dangerous?

If these objects are recycled with leftover information, one user’s request could leak data into another user’s request. This can possibly lead to:

Session data leaking.

- Cross-user/request information leakage.

Malicious attackers might try to trigger this bug deliberately to extract sensitive information.

Apache Tomcat 9..96

Fixed versions:

9..97

Reference:
- Tomcat CVE-2024-52318 Security Advisory
- Tomcat Official Security Page

How the Flaw Happens—A Code Example

Let’s look at a simplified Java code snippet that shows how improper object reuse can happen.

public class SimpleRecycler {
    private final Object[] pool = new Object[10];
    private int pointer = ;
    
    public void recycle(Object obj) {
        pool[pointer] = obj;      // put object back into pool
        pointer = (pointer + 1) % pool.length;
    }

    public Object get() {
        return pool[pointer];     // get object from pool
    }
}

public class HttpRequest {
    public String userData;
    // ... other fields
}

public class Example {
    public static void main(String[] args) {
        SimpleRecycler recycler = new SimpleRecycler();
        HttpRequest req1 = new HttpRequest();
        req1.userData = "AdminSessionToken";
        recycler.recycle(req1);

        // Next request picks up recycled object
        HttpRequest req2 = (HttpRequest) recycler.get();
        System.out.println("Leaked Data: " + req2.userData); // Oops! Still contains admin’s session info!
    }
}

If userData was not cleared, sensitive information leaks.

In Tomcat’s real code, similar issues can occur with more complex request/response objects.

In shared hosting environments or applications handling sensitive data, this is particularly nasty.

Proof-of-Concept (Conceptual)

Since this is a server-internal bug, it’s challenging to show a direct “exploit”, but the idea is this:

# 1. Attacker sends a private data payload
curl -X POST -d 'secret=malicious-data' https://example.com/endpoint1

# 2. Immediately, attacker (or another user) sends another request
curl -X GET https://example.com/endpoint2

# If Tomcat recycles objects improperly, response from endpoint2 could include the "malicious-data" posted to endpoint1!

- NVD CVE-2024-52318 Summary
- Apache Tomcat Security Pages
- Release Notes

Conclusion

CVE-2024-52318 is a reminder that performance tricks—like recycling objects—can introduce subtle security problems if not done with care. If you’re a Tomcat admin or developer, update your server as soon as possible. The fix is out, and it’s your best defense.

Stay safe, and always keep an eye on your dependencies!


*This article is exclusive content written for educational purposes. For more details, always refer to the original Tomcat advisories and official CVE references.*

Timeline

Published on: 11/18/2024 13:15:04 UTC
Last modified on: 11/18/2024 17:11:17 UTC