CVE-2020-1591
📋 TL;DR
This is a cross-site scripting (XSS) vulnerability in Microsoft Dynamics 365 (on-premises) where improper input sanitization allows authenticated attackers to inject malicious scripts. Successful exploitation enables attackers to perform actions as the authenticated user, including reading unauthorized content, modifying permissions, and deleting data. Only on-premises Dynamics 365 deployments with authenticated user access are affected.
💻 Affected Systems
- Microsoft Dynamics 365 (on-premises)
📦 What is this software?
Dynamics 365 by Microsoft
⚠️ Risk & Real-World Impact
Worst Case
Attacker gains full control over Dynamics 365 instance, steals sensitive business data, modifies or deletes critical information, and uses compromised accounts for lateral movement within the network.
Likely Case
Attacker steals session cookies or authentication tokens, accesses sensitive business data, performs unauthorized actions within Dynamics 365, and potentially compromises additional user accounts.
If Mitigated
Limited impact due to proper input validation, web application firewalls, and least privilege access controls preventing script execution and limiting damage scope.
🎯 Exploit Status
Requires authenticated access to Dynamics 365. Attack involves crafting malicious web requests with script payloads that bypass input sanitization.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Apply Microsoft security update from October 2020
Vendor Advisory: https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2020-1591
Restart Required: Yes
Instructions:
1. Download the security update from Microsoft Update Catalog. 2. Apply the update to all affected Dynamics 365 servers. 3. Restart the Dynamics 365 services. 4. Test functionality after patching.
🔧 Temporary Workarounds
Implement Web Application Firewall
allDeploy WAF with XSS protection rules to filter malicious requests
Content Security Policy
allImplement CSP headers to restrict script execution sources
🧯 If You Can't Patch
- Implement strict input validation and output encoding for all user-supplied data
- Apply principle of least privilege to Dynamics 365 user accounts and monitor for suspicious activity
🔍 How to Verify
Check if Vulnerable:
Check Dynamics 365 version and patch status; if running unpatched on-premises version from before October 2020, assume vulnerableCheck Version:
Check Dynamics 365 Server version through administration console or PowerShell: Get-Command -Module Microsoft.Dynamics*Verify Fix Applied:
Verify that security update KB4578950 or later is installed and Dynamics 365 version is updated📡 Detection & Monitoring
Log Indicators:
- Unusual POST requests with script tags or JavaScript payloads
- Multiple failed authentication attempts followed by successful login and script-like requests
- Unexpected changes to user permissions or content deletions
Network Indicators:
- HTTP requests containing <script> tags or JavaScript code in parameters
- Unusual outbound connections from Dynamics server following suspicious requests
SIEM Query:
source="dynamics_logs" AND (http_request CONTAINS "<script>" OR http_request CONTAINS "javascript:" OR http_request CONTAINS "onerror=" OR http_request CONTAINS "onload=")