CVE-2023-38836: File Upload vulnerability in BoidCMS v.2.. Allows Remote Code Execution Via GIF Header Bypass

A new critical vulnerability (CVE-2023-38836) has been discovered in the popular content management system (CMS), BoidCMS v.2... This vulnerability could allow an attacker to execute arbitrary code on a victim's server by bypassing the MIME type validation process through adding a GIF header to the uploaded file. In this post, we will provide in-depth technical details on this vulnerability, explain how it can be exploited, and examine the implications of such an exploit.

What is the Vulnerability?

BoidCMS v.2.. is a popular content management system that allows users to create and manage their websites with ease. The vulnerability exists in the file upload functionality provided by the CMS, which is supposed to strictly accept only image files with specific MIME types. However, it has been discovered that an attacker can bypass this security measure and upload malicious PHP files by simply adding a GIF header to the file. This allows the attacker to execute arbitrary code on the victim's server, potentially compromising the website and leading to severe consequences.

Technical Details and Code Snippet

When uploading a file to BoidCMS v.2.., the CMS checks the MIME type of the file to ensure that it's a supported image format (e.g. JPEG, PNG, or GIF). However, the MIME type check can be bypassed by adding a GIF header to the file, tricking the CMS into thinking the uploaded file is a valid image file. After bypassing the check, the attacker can upload a PHP file with the GIF header, allowing them to execute arbitrary code on the server hosting the victim's website.

Here's an example of how the GIF header can be added to a PHP file to exploit this vulnerability

GIF89a
<?php
// Arbitrary code to be executed on the server
echo 'Vulnerable server!';
?>

By placing the GIF89a header at the beginning of the PHP file, the file will be uploaded successfully, bypassing the MIME type check in BoidCMS v.2... Once uploaded, the attacker can access the file through a direct URL, triggering the execution of the malicious PHP code on the server.

Exploit Details

To exploit this vulnerability, an attacker needs to have valid credentials to access the CMS's admin panel. The steps to exploit this vulnerability are described below:

Step 1: Prepare the malicious PHP file by adding a GIF header at the beginning of the file, as shown in the code snippet above.

Step 2: Log in to the BoidCMS admin panel using valid credentials.

Step 3: Navigate to the file upload feature and select the prepared malicious file.

Step 4: Upload the file. The server-side validation will pass since the file appears to be a valid GIF image.

Step 5: Access the uploaded file's URL, triggering the execution of the PHP code on the server.

The vulnerability was first documented in the following resources

- Original Advisory
- CVE-2023-38836 Details
- BoidCMS Official Website

Conclusion

CVE-2023-38836 is a critical vulnerability in BoidCMS v.2.. that allows an attacker to execute arbitrary code on a victim's server by bypassing the MIME type check using a GIF header. To mitigate the potential risk of this exploit, it is recommended that users of BoidCMS v.2.. urgently update their CMS to the latest version, which contains the necessary security patches.

It is important for developers to ensure strict server-side validation checks to reduce the risk of similar vulnerabilities in the future. Additionally, users should always maintain strong credentials and keep their CMS software up-to-date to protect their websites against possible exploits.

Timeline

Published on: 08/21/2023 17:15:47 UTC
Last modified on: 10/10/2023 17:15:12 UTC