CVE-2023-5822 - Arbitrary File Upload Vulnerability in Drag and Drop Multiple File Upload

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Summary: In this post, we will discuss CVE-2023-5822, a critical vulnerability that allows an unauthenticated attacker to upload arbitrary files in the popular WordPress plugin Drag and Drop Multiple File Upload - Contact Form 7. We will also provide code snippets and links to original references to help you understand how the exploit works and how to mitigate the risks.

Introduction

Contact Form 7 is one of the most popular contact form plugins for WordPress, and its extension plugin, Drag and Drop Multiple File Upload - Contact Form 7, adds multiple file upload functionality to the form. Unfortunately, a significant vulnerability (CVE-2023-5822) was discovered in the plugin, affecting versions up to and including 1.3.7.3. This vulnerability allows unauthenticated attackers to upload arbitrary files and potentially execute remote code on the affected site's server.

The root cause of the vulnerability is insufficient file type validation in the 'dnd_upload_cf7_upload' function. An attacker could exploit this vulnerability if an authorized user, such as an editor or administrator, has added a multiple file upload form field with '*' as the acceptable file types.

Here's a code snippet highlighting the vulnerable part of the dnd_upload_cf7_upload function

function dnd_upload_cf7_upload($uploaded_files) {
    // ... code omitted for brevity
    // check if file type is allowed
    $filetype_pattern = strtolower($cf7_filetype_pattern);
    if (!preg_match('/^(' . $filetype_pattern . ')$/i', $file_ext)) {
        // throw error, file type not allowed
        // ... code omitted for brevity
    } else {
        // process file upload
        // ... code omitted for brevity
    }

    // ... code omitted for brevity
    
    return $uploaded_files;
}

As you can see in this snippet, the function tries to validate the file extension of the uploaded file against the 'filetype_pattern' field. However, when an authorized user adds a multiple file upload form field with '*' as the acceptable file types, this validation step becomes pointless, as any file type would be allowed to pass through.

Exploiting this vulnerability

An attacker can create a script that uploads an arbitrary file to the vulnerable server using a specially crafted form submission. This file could contain malicious code (such as PHP backdoors or webshells), which can be executed remotely once it's uploaded.

Mitigation

The best way to mitigate this risk is to update the Drag and Drop Multiple File Upload - Contact Form 7 plugin to version 1.3.7.4 or later. However, if you cannot update the plugin or if you're using an affected version, here are some additional precautions you can take:

1. Avoid using '*' as the acceptable file types for the multiple file upload field in your forms. Instead, provide a specific list of allowed file types (e.g. 'jpg, png, gif').
2. Restrict form submissions to authenticated users to minimize the risk of an unauthenticated attacker exploiting the vulnerability.

Original References

To get more information about the vulnerability and the affected plugin, refer to the following resources:
1. CVE-2023-5822 - Drag and Drop Multiple File Upload - Contact Form 7 Vulnerability
2. WordPress Plugin Repository - Drag and Drop Multiple File Upload - Contact Form 7

Conclusion

The CVE-2023-5822 vulnerability in the Drag and Drop Multiple File Upload - Contact Form 7 plugin poses a serious risk to the security of WordPress sites that are running an affected version. It's crucial to address this issue by updating the plugin and applying the recommended mitigation strategies to ensure your site remains safe from unauthenticated attackers.

Timeline

Published on: 11/22/2023 16:15:15 UTC
Last modified on: 11/29/2023 19:15:14 UTC