CVE-2023-44763: Arbitrary File Upload Vulnerability in Concrete CMS v9.2.1 Leads to Cross-Site Scripting (XSS) Exploitation

Concrete CMS v9.2.1 was found to be affected by an Arbitrary File Upload vulnerability via a Thumbnail file upload, which allows attackers to perform Cross-Site Scripting (XSS) attacks. This poses a significant security risk as an attacker could potentially execute malicious code on the affected web application, possibly leading to data theft, service disruption, or other damages. The CVE number assigned to this vulnerability is CVE-2023-44763.

It should be noted that the vendor's position is that customers are supposed to know that they must exclude "pdf" from the allowed file types, even though pdf is, by default, one of the allowed file types in the configuration.

Technical Details

To successfully exploit this vulnerability, an attacker must upload a specially crafted Thumbnail file containing malicious code. The code should be embedded within a PDF file, which is allowed by default, making it easier for an attacker to bypass any security measures in place.

Below is a code snippet demonstrating the issue

<?php
// Thumbnail.php
// ...

public function create($type, $path, $width = null, $height = null)
{
    // ...
    // Create the thumbnail using one of the supported file types
    if ($type == FileType::T_PDF) {
        // This code allows an attacker to upload a malicious pdf file
        $img = $this->pdfToThumbnail($path, $width, $height);
    } else {
        // ...
    }
    // ...
}

// ...
?>

To successfully exploit this vulnerability, follow these steps

1. Prepare a malicious PDF file with embedded JavaScript or other forms of payloads capable of executing XSS attacks.

Login to Concrete CMS and access the "File Manager" section.

3. Upload the malicious PDF file with a valid thumbnail image, such as a JPEG or PNG file. As a result, the thumbnail will be generated, and the embedded payload will be executed.

4. When an unsuspecting user or admin previews or clicks on the thumbnail, the XSS payload will execute, allowing the attacker to perform malicious activities such as stealing session cookies or executing arbitrary commands on the affected user's machine.

Update to the latest version of Concrete CMS if security patches are available.

2. Ensure that you properly configure the allowed file types in your installation to exclude potentially harmful file types such as "pdf" or other unsafe formats.

3. Implement strict content security policies to help mitigate the potential effects of an XSS attack, such as preventing inline scripts from executing, only allowing scripts from trusted sources, and sanitizing user input.

4. Keep your web server and its associated software components up-to-date and regularly apply the latest security patches.

5. Educate users about the risks associated with clicking on unfamiliar or untrusted links and attachments, as well as the importance of keeping their software up-to-date.

Links and Original References

- CVE-2023-44763 Official CVE Record
- Concrete CMS Official Website
- Concrete CMS GitHub Repository

Disclaimer

The information provided in this article is for educational purposes only. Any actions taken based on the contents of this article are at the reader's discretion and responsibility. The author and publisher will not be held responsible for any damages or losses that may occur as a result of using this information.

Timeline

Published on: 10/10/2023 12:15:09 UTC
Last modified on: 11/07/2023 04:21:40 UTC