CVE-2020-1025
📋 TL;DR
CVE-2020-1025 is an authentication bypass vulnerability in Microsoft SharePoint Server and Skype for Business Server where improper OAuth token validation allows attackers to modify tokens and gain unauthorized access. Organizations using affected versions of these Microsoft products are vulnerable. The vulnerability has a critical CVSS score of 9.8 due to its potential for complete system compromise.
💻 Affected Systems
- Microsoft SharePoint Server
- Microsoft Skype for Business Server
📦 What is this software?
Lync by Microsoft
⚠️ Risk & Real-World Impact
Worst Case
Complete system takeover where an attacker gains administrative privileges, accesses sensitive data, and potentially deploys ransomware or other malware across the enterprise.
Likely Case
Unauthorized access to sensitive SharePoint documents, user data, or Skype communications, potentially leading to data theft, espionage, or further lateral movement within the network.
If Mitigated
Limited impact with proper network segmentation, strong authentication controls, and monitoring that detects anomalous token usage patterns.
🎯 Exploit Status
Attack requires token modification capability; Microsoft has not disclosed specific exploitation details
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Apply Microsoft security updates from May 2020 or later
Vendor Advisory: https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2020-1025
Restart Required: Yes
Instructions:
1. Download and install the May 2020 security updates for SharePoint Server and Skype for Business Server. 2. Apply updates through Windows Server Update Services (WSUS) or Microsoft Update. 3. Restart affected servers after patch installation.
🔧 Temporary Workarounds
Disable OAuth authentication
windowsTemporarily disable OAuth token-based authentication if not required for business operations
Network segmentation
allIsolate SharePoint and Skype servers from internet and restrict internal access
🧯 If You Can't Patch
- Implement strict network access controls to limit who can reach SharePoint and Skype servers
- Enable detailed logging of authentication events and monitor for anomalous token usage patterns
🔍 How to Verify
Check if Vulnerable:
Check if SharePoint Server or Skype for Business Server versions are before May 2020 security updatesCheck Version:
For SharePoint: Get-SPFarm | Select BuildVersion; For Skype: Get-CsServerVersionVerify Fix Applied:
Verify that May 2020 or later security updates are installed on affected servers📡 Detection & Monitoring
Log Indicators:
- Failed authentication attempts with modified tokens
- Unusual OAuth token validation errors
- Authentication events from unexpected sources
Network Indicators:
- Unusual authentication traffic patterns to SharePoint/Skype servers
- Token manipulation attempts in HTTP headers
SIEM Query:
source="SharePoint" OR source="Skype" AND (event_id=4625 OR event_id=4771) AND token_validation_failure