CVE-2020-16878
📋 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 authenticated users, potentially allowing 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
Dynamics 365 by Microsoft
⚠️ Risk & Real-World Impact
Worst Case
An authenticated attacker could gain administrative privileges, exfiltrate sensitive business data, modify or delete critical information, and maintain persistent access through backdoors.
Likely Case
An authenticated user with malicious intent could steal session cookies, perform actions as other users, modify permissions, or deface internal applications.
If Mitigated
With proper input validation and output encoding controls, the risk is limited to authenticated users who would need to bypass additional security layers.
🎯 Exploit Status
Exploitation requires authenticated access to Dynamics 365 and knowledge of vulnerable endpoints. No public exploit code was available at disclosure time.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Refer to Microsoft security update for specific version
Vendor Advisory: https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2020-16878
Restart Required: Yes
Instructions:
1. Review Microsoft security advisory for affected versions. 2. Apply the security update through Microsoft Update or download from Microsoft Update Catalog. 3. Restart Dynamics 365 services and affected servers. 4. Test functionality after patching.
🔧 Temporary Workarounds
Input Validation Enhancement
windowsImplement additional input validation and output encoding for Dynamics 365 web requests
Configuration through Dynamics 365 administration console and web.config modifications
Content Security Policy
windowsImplement strict Content Security Policy headers to limit script execution
Add CSP headers via IIS configuration or web.config: Content-Security-Policy: default-src 'self'
🧯 If You Can't Patch
- Implement web application firewall (WAF) rules to block XSS payloads in requests to Dynamics endpoints
- Restrict access to Dynamics 365 to only necessary users and implement principle of least privilege
🔍 How to Verify
Check if Vulnerable:
Check Dynamics 365 version against Microsoft security advisory; test for XSS vulnerabilities in web request parametersCheck Version:
Check Dynamics 365 version through administration console or review installed updates in Control PanelVerify Fix Applied:
Verify patch installation through Windows Update history or version check; test previously vulnerable endpoints with XSS payloads📡 Detection & Monitoring
Log Indicators:
- Unusual POST/GET requests with script tags or JavaScript payloads to Dynamics endpoints
- Multiple failed authentication attempts followed by successful login and suspicious requests
Network Indicators:
- HTTP requests containing <script>, javascript:, or encoded XSS payloads to Dynamics servers
- Unusual outbound connections following Dynamics server access
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=")