In this post, we will discuss a critical vulnerability (CVE-2024-38828) affecting Spring MVC controllers utilizing @RequestBody byte[] method parameters. Attackers can exploit this vulnerability to launch a Denial of Service (DoS) attack, potentially bringing down the affected application.

This vulnerability arises when a Spring MVC controller defines a method with an @RequestBody byte[] parameter. Before diving into the details, let's understand what Spring MVC and its @RequestBody annotation is all about.

Spring MVC – A Brief Overview

Spring MVC is a popular Java-based web application framework, allowing developers to build scalable and modern web applications. It provides a flexible platform to develop web applications handling HTTP requests and responses with plenty of built-in features for managing Controller, Model, and View components seamlessly.

The @RequestBody annotation in Spring MVC plays a vital role in binding HTTP request payload data to the method parameters within a controller. Developers use this annotation to automatically parse incoming JSON/XML data into Java objects.

The Vulnerability: CVE-2024-38828

Now that we have a basic understanding of Spring MVC, let's explore the vulnerability in question. CVE-2024-38828 affects Spring MVC controller methods accepting @RequestBody byte[] parameters. Here's an example of a potentially vulnerable method:

@RequestMapping(value = "/upload", method = RequestMethod.POST)
public ResponseEntity<String> upload(@RequestBody byte[] fileContent) {
    // Process fileContent...
    return new ResponseEntity<>("File Uploaded Successfully", HttpStatus.OK);
}

This method is called whenever an HTTP POST request is made to the "/upload" endpoint. The request payload, consisting of raw bytes, is passed directly to the fileContent parameter. The vulnerability lies in the way Spring MVC processes this byte[] parameter when the @RequestBody annotation is involved.

An attacker may craft an HTTP POST request with a large payload, loading the entire payload data into the byte[] parameter. Since it is a raw array of bytes, the server might allocate a large amount of memory, potentially maxing out the system's available resources, leading to a DoS attack.

Original References and Reporting

The vulnerability was first reported by XYZ Security Researcher (link to original researcher's report) and has been assigned the CVE identifier CVE-2024-38828. The vulnerability was acknowledged by the Spring team, and an official advisory was released (link to the Spring advisory).

Exploiting the Vulnerability

To exploit this vulnerability, an attacker could craft an HTTP POST request with an unusually large body payload targeting a vulnerable Spring MVC endpoint. Here is a sample exploit using curl:

# Generate a 1 GB file filled with zeros
dd if=/dev/zero of=payload.bin bs=1M count=1024

# Send the payload to the vulnerable endpoint
curl -X POST -H "Content-Type: application/octet-stream" --data-binary @payload.bin http://example.com/upload

How to Mitigate

As an immediate mitigation, developers can limit the maximum allowed size of an incoming request payload by configuring the property spring.http.multipart.max-request-size. While this measure prevents exceptionally large requests from consuming resources, it is still essential to apply proper fixes or implement more secure alternatives.

The Spring Team has released patch versions containing a fix for this vulnerability. Developers should update their Spring MVC versions to the latest patch release to eliminate the vulnerability.

Another possible solution is to avoid using @RequestBody byte[] method parameters and instead leverage Java's MultipartFile or other streaming-based file handling options that help process file data without loading the entire content into memory.

Here's an example of how to use MultipartFile to handle uploaded files

@RequestMapping(value = "/upload", method = RequestMethod.POST)
public ResponseEntity<String> upload(@RequestParam("file") MultipartFile file) throws IOException {
    // Process file content using file.getInputStream()
    return new ResponseEntity<>("File Uploaded Successfully", HttpStatus.OK);
}

With this change, the file content is not loaded entirely into memory, significantly improving resource utilization and mitigating the vulnerability.

Stay safe and always keep your dependencies up-to-date! Remember, always consider security best practices when working with sensitive data or critical applications like file uploads.

Timeline

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