In September 2023, a security vulnerability was found in Hutool, a popular Java utility library. It was logged as CVE-2023-42276. The problem is a buffer overflow found in version 5.8.21 through the jsonArray component. Buffer overflows can let attackers crash services or even run their own code on your system. In this article, we’ll explain how this vulnerability happens, show proof with code, reference resources for further reading, and break down how an attacker could exploit it.

1. What is Hutool?

Hutool is a popular open-source Java library. It helps with a lot of common coding tasks, including date handling, text, files, HTTP, and JSON processing. The JSON part includes the jsonArray class, which helps parse and create JSON arrays.

What is CVE-2023-42276?

CVE-2023-42276 identifies a buffer overflow issue in Hutool v5.8.21. The vulnerability lies in the way Hutool's JSONArray processes overly large or unexpectedly crafted JSON arrays.

Original disclosure:
- NVD - CVE-2023-42276
- GitHub Advisory

3. Vulnerable Code Example

The bug sits in insufficient checks when copying or adding new items to a JSONArray. Here's how you could trigger the overflow through user input.

Example Vulnerable Code

import cn.hutool.json.JSONArray;

public class VulnerableExample {
    public static void main(String[] args) {
        // Malicious input: huge or malformed string
        String jsonInput = "[1,2,3," + ",".repeat(100000) + "4]";
        JSONArray jsonArray = new JSONArray(jsonInput);  // Triggers processing

        System.out.println("Length: " + jsonArray.size());
    }
}

On some Java VMs, this can overflow internal buffers or crash your service.

- In worst cases (native array handling or custom JVM), this could overwrite memory areas—leading to code execution.

Supply Large Payloads:

Attackers send huge, deeply nested, or oddly crafted JSON arrays to endpoints using Hutool's JSONArray.

At best, your app is DoSed (denial-of-service).

- At worst, the attacker can cause code execution if the memory layout is just right or if used in non-sandboxed environments.

How it might look

curl -X POST "http://victim.com/parse_json"; \
    -H "Content-Type: application/json" \
    -d '[1,2,3,,,,....,4]'

This would crash the backend service if it uses the vulnerable Hutool version and naively parses the body.

Upgrade Hutool:

The developers patched the bug in later versions (See Changelog). Upgrade to at least v5.8.22 or higher.

6. References

- NVD CVE-2023-42276
- Hutool Issue Tracker
- Official Hutool Release Notes

7. Summary

CVE-2023-42276 is a dangerous buffer overflow bug in Hutool v5.8.21’s JSON array handling. It can take down your Java app or worse—let hackers run arbitrary code. Make sure you upgrade Hutool and never trust unchecked user input. Stay safe!


Want to test for this bug or double-check your systems? Use the sample code above and see if your system can safely reject large or malformed JSON arrays. If not, patch today!

Timeline

Published on: 09/08/2023 22:15:11 UTC
Last modified on: 09/13/2023 00:35:56 UTC