CVE-2024-21393
📋 TL;DR
This is a cross-site scripting (XSS) vulnerability in Microsoft Dynamics 365 on-premises that allows attackers to inject malicious scripts into web pages viewed by other users. Attackers could steal session cookies, redirect users to malicious sites, or perform actions on behalf of authenticated users. Only organizations running on-premises Dynamics 365 deployments are affected.
💻 Affected Systems
- Microsoft Dynamics 365 (on-premises)
📦 What is this software?
Dynamics 365 by Microsoft
⚠️ Risk & Real-World Impact
Worst Case
Attackers could steal administrator credentials, hijack user sessions, redirect users to phishing sites, or perform unauthorized actions in the Dynamics 365 application as authenticated users.
Likely Case
Attackers would typically steal session cookies or user credentials, potentially leading to unauthorized access to sensitive business data within Dynamics 365.
If Mitigated
With proper input validation and output encoding controls, the impact would be limited to minor UI disruption without data compromise.
🎯 Exploit Status
XSS vulnerabilities typically have low exploitation complexity. Attackers need to trick users into interacting with malicious content, but no authentication bypass is required for the injection itself.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: February 2024 security update for Dynamics 365
Vendor Advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2024-21393
Restart Required: Yes
Instructions:
1. Download the February 2024 security update from Microsoft Update Catalog. 2. Apply the update to all Dynamics 365 on-premises servers. 3. Restart the Dynamics 365 services. 4. Test application functionality after patching.
🔧 Temporary Workarounds
Implement Content Security Policy (CSP)
allConfigure CSP headers to restrict script execution to trusted sources only
Enable Input Validation
allConfigure web application firewall or application-level input validation to filter malicious scripts
🧯 If You Can't Patch
- Implement strict Content Security Policy (CSP) headers to prevent script execution from untrusted sources
- Deploy a web application firewall (WAF) with XSS protection rules enabled
🔍 How to Verify
Check if Vulnerable:
Check if your Dynamics 365 on-premises installation has the February 2024 security update applied. If not, assume vulnerable.Check Version:
Check Dynamics 365 server version through administrative console or PowerShell: Get-WmiObject -Class Win32_Product | Where-Object {$_.Name -like '*Dynamics*'}Verify Fix Applied:
Verify the patch is installed via Windows Update history or by checking Dynamics 365 version/build numbers against patched versions.📡 Detection & Monitoring
Log Indicators:
- Unusual script tags or JavaScript in URL parameters
- Multiple failed XSS attempts in web server logs
- Suspicious user agent strings containing script payloads
Network Indicators:
- HTTP requests containing script tags or JavaScript in parameters
- Unusual redirect patterns from Dynamics 365 pages
SIEM Query:
source="web_server_logs" AND (url="*<script*" OR url="*javascript:*" OR url="*onload=*" OR url="*onerror=*")