CVE-2020-16872
📋 TL;DR
This is a cross-site scripting (XSS) vulnerability in Microsoft Dynamics 365 (on-premises) that allows authenticated attackers to inject malicious scripts into web requests. When exploited, these scripts execute in the security context of the current authenticated user, potentially enabling unauthorized data access, privilege escalation, and content manipulation. Only organizations running vulnerable on-premises Dynamics 365 installations are affected.
💻 Affected Systems
- Microsoft Dynamics 365 (on-premises)
📦 What is this software?
Dynamics 365 by Microsoft
⚠️ Risk & Real-World Impact
Worst Case
An authenticated attacker could gain administrative privileges, exfiltrate sensitive business data, delete critical content, and maintain persistent access through backdoors.
Likely Case
An authenticated user with limited privileges could escalate their permissions, access unauthorized data, and perform actions like modifying records or deleting content.
If Mitigated
With proper input validation and output encoding controls, the vulnerability would be prevented, though the underlying code flaw would still exist.
🎯 Exploit Status
Exploitation requires authenticated access to the Dynamics server. The vulnerability involves improper input sanitization in web requests, which is a common attack vector.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Security update released October 2020 (specific version depends on Dynamics 365 build)
Vendor Advisory: https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2020-16872
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 Input Validation
allAdd server-side validation for all user inputs to reject malicious scripts before processing.
Enable Content Security Policy (CSP)
allConfigure CSP headers to restrict script execution sources and mitigate XSS impact.
🧯 If You Can't Patch
- Restrict user permissions to minimum required levels to limit potential damage from exploitation.
- Implement web application firewall (WAF) rules to detect and block XSS payloads in requests.
🔍 How to Verify
Check if Vulnerable:
Check Dynamics 365 version against patched versions in Microsoft advisory. Review server logs for suspicious script injection attempts.Check Version:
Check Dynamics 365 version through the application interface or server installation logs.Verify Fix Applied:
Verify the security update is installed via Windows Update history or Dynamics 365 version check. Test with safe XSS payloads to confirm sanitization.📡 Detection & Monitoring
Log Indicators:
- Unusual POST/GET requests containing script tags or JavaScript code
- Multiple failed authentication attempts followed by successful logins with script injection patterns
Network Indicators:
- HTTP requests with encoded script payloads in parameters
- Unexpected outbound connections from Dynamics server after suspected exploitation
SIEM Query:
source="dynamics_logs" AND (http_request CONTAINS "<script>" OR http_request CONTAINS "javascript:")