A critical vulnerability, CVE-2023-24998, has been discovered in Apache Commons FileUpload before version 1.5 which may leave your system susceptible to Denial of Service (DoS) attacks. The root cause of this vulnerability lies in the lack of a limit imposed on the number of request parts processed during file uploads. In this post, we will discuss the vulnerability in detail, provide a code snippet to illustrate the problem, and outline the steps needed to mitigate this vulnerability in your system.

Vulnerability Details

The Apache Commons FileUpload library is a widely used Java package to handle file uploads in web applications. However, before version 1.5, this library does not impose a limit on the number of request parts (e.g., uploaded files, form fields) that can be processed. This oversight allows an attacker to craft a malicious file upload or a series of uploads, leading to a DoS attack.

Exploiting this vulnerability would consume server resources (CPU, memory), potentially leading to a service outage or a severe degradation in a system's performance. This vulnerability is identified by the CVE identifier CVE-2023-24998.

Code Snippet

In vulnerable versions of the Apache Commons FileUpload library (<1.5), there is no invocation of FileUploadBase#setFileCountMax method to limit the maximum number of request parts processed. 

ServletFileUpload upload = new ServletFileUpload();

// Without this line, an attacker can force the server to process an unlimited number of request parts.
// upload.setFileCountMax(MAX_ALLOWED_FILES);

Mitigation

To mitigate this vulnerability, it is necessary to update Apache Commons FileUpload to version 1.5 or later. This version introduces the FileUploadBase#setFileCountMax method, which allows developers to explicitly set a maximum limit on the number of request parts processed.

Here's an example of how to configure the maximum allowable file count

import org.apache.commons.fileupload.servlet.ServletFileUpload;

public class FileUploadConfiguration {

    public void configure() {
        ServletFileUpload upload = new ServletFileUpload();
        final int MAX_ALLOWED_FILES = 100;

        // Enable this line to limit the number of request parts processed.
        upload.setFileCountMax(MAX_ALLOWED_FILES);
    }
}

Remember that this new configuration option is not enabled by default, so you must explicitly configure it in order to protect your system from potential DoS attacks.

References

1. Original Apache Commons FileUpload Advisory: https://commons.apache.org/proper/commons-fileupload/patches.html
2. Download Apache Commons FileUpload 1.5: https://commons.apache.org/proper/commons-fileupload/download_fileupload.cgi
3. CVE-2023-24998 Details: https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2023-24998
4. Apache Commons FileUpload Documentation: https://commons.apache.org/proper/commons-fileupload/index.html

Conclusion

It is essential to protect your systems from potential DoS attacks by addressing this vulnerability, CVE-2023-24998, found in Apache Commons FileUpload versions before 1.5. To mitigate the risk, ensure you update to FileUpload 1.5 or later and explicitly configure the maximum file count limit using the FileUploadBase#setFileCountMax method in your code. Keep your libraries up-to-date to minimize the risk of security vulnerabilities impacting your systems in the future.

Timeline

Published on: 02/20/2023 16:15:00 UTC
Last modified on: 03/01/2023 15:09:00 UTC