CVE-2023-43498 - Jenkins Processing File Uploads Security Flaw in MultipartFormDataParser Lets Attackers Access Temporary Files

The world of cybersecurity is a rapidly changing landscape, with new vulnerabilities and security risks constantly being discovered. It is crucial for software developers and administrators to stay up-to-date on the latest security flaws affecting their systems. In this post, we will discuss a recently discovered security flaw in Jenkins, a widely utilized automation server, known as CVE-2023-43498.

Overview

Jenkins is commonly used to handle the building, testing, and deploying stages of software development projects. It is an open-source tool that automates these processes, saving developers time and resources. With its popularity and extensive use, ensuring the security and privacy of Jenkins is essential.

CVE-2023-43498 refers to a security vulnerability within Jenkins versions 2.423 and earlier, as well as LTS (Long Term Support) 2.414.1 and earlier. This flaw allows attackers with access to the Jenkins controller's file system to read and write temporary files generated during the processing of file uploads. The root of this issue lies in the use of MultipartFormDataParser, which creates these temporary files in the default system temporary directory with the default permissions for new files.

Exploit Details

When processing file uploads, Jenkins uses the MultipartFormDataParser to create temporary files. These files are stored in the default system temporary directory with the default permissions for new files. As a result, attackers with access to the Jenkins controller file system can potentially read and write these files before they are used in the system, presenting a security risk.

Code Snippet

Below is a simple code snippet demonstrating the process of creating a temporary file in Jenkins (Java):

@Path("/upload")
public class FileUploadResource {

    @POST
    @Consumes(MediaType.MULTIPART_FORM_DATA)
    public Response uploadFile(@FormDataParam("file") InputStream uploadedInputStream,
            @FormDataParam("file") FormDataContentDisposition fileDetail) {

        MultipartFormDataParser parser = new MultipartFormDataParser();
        ...
        File tempFile = parser.createTempFile(uploadedInputStream);
        ...
    }
}

The 'parser.createTempFile()' function creates temporary files in the default system directory with the default permissions for new files.

Mitigation and Recommendations

The vulnerability has been addressed in Jenkins 2.424 and LTS 2.414.2. It is essential for users to upgrade to these versions or later to protect against this security risk.

The Jenkins project team has published an advisory detailing this vulnerability and providing additional information on the mitigation strategy: Jenkins Security Advisory 2023-11-19.

In addition to upgrading your Jenkins instance, administrators should also take the following steps to enhance the security of their systems:

1. Restrict access to the Jenkins controller file system by implementing proper access controls and permissions.
2. Regularly monitor and audit your Jenkins environment to identify and address potential security risks.
3. Educate your development team about the importance of secure coding practices and staying informed on the latest security vulnerabilities.

Conclusion

CVE-2023-43498 is a security vulnerability that affects Jenkins versions 2.423 and earlier, and LTS 2.414.1 and earlier. This flaw allows attackers with access to the Jenkins controller file system to read and write temporary files generated by the MultipartFormDataParser during the processing of file uploads. To protect your Jenkins environment from potential exploits related to this vulnerability, it is essential to upgrade to Jenkins 2.424 or LTS 2.414.2 and follow the recommended security guidelines.

Timeline

Published on: 09/20/2023 17:15:00 UTC
Last modified on: 09/23/2023 03:45:00 UTC