CVE-2020-0646
📋 TL;DR
CVE-2020-0646 is a remote code execution vulnerability in Microsoft .NET Framework where improper input validation allows attackers to inject and execute arbitrary code. This affects systems running vulnerable .NET Framework versions, particularly when processing untrusted XOML files in SharePoint workflows. Organizations using affected Microsoft products are at risk.
💻 Affected Systems
- Microsoft .NET Framework
- Microsoft SharePoint Server
📦 What is this software?
.net Framework by Microsoft
.net Framework by Microsoft
.net Framework by Microsoft
.net Framework by Microsoft
.net Framework by Microsoft
.net Framework by Microsoft
.net Framework by Microsoft
.net Framework by Microsoft
.net Framework by Microsoft
.net Framework by Microsoft
.net Framework by Microsoft
.net Framework by Microsoft
.net Framework by Microsoft
.net Framework by Microsoft
.net Framework by Microsoft
.net Framework by Microsoft
.net Framework by Microsoft
.net Framework by Microsoft
.net Framework by Microsoft
.net Framework by Microsoft
.net Framework by Microsoft
.net Framework by Microsoft
.net Framework by Microsoft
.net Framework by Microsoft
.net Framework by Microsoft
.net Framework by Microsoft
.net Framework by Microsoft
.net Framework by Microsoft
⚠️ Risk & Real-World Impact
Worst Case
Full system compromise allowing attacker to execute arbitrary code with the privileges of the application, potentially leading to data theft, ransomware deployment, or complete system takeover.
Likely Case
Remote code execution leading to unauthorized access, data exfiltration, or lateral movement within the network.
If Mitigated
Limited impact with proper network segmentation, least privilege principles, and security controls preventing successful exploitation.
🎯 Exploit Status
Exploitation requires the ability to upload or inject XOML content into SharePoint workflows. Public proof-of-concept code exists and has been used in real attacks.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: January 2020 Security Update for .NET Framework
Vendor Advisory: https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2020-0646
Restart Required: Yes
Instructions:
1. Apply the January 2020 Security Update for .NET Framework from Windows Update. 2. For SharePoint Server, apply the corresponding SharePoint security update. 3. Restart affected systems after patching.
🔧 Temporary Workarounds
Disable XOML workflow processing
windowsPrevent SharePoint from processing XOML workflow files to block the attack vector
Modify SharePoint configuration to disable XOML workflow processing
Network segmentation
allIsolate SharePoint servers from internet and restrict internal access
🧯 If You Can't Patch
- Implement strict access controls to prevent unauthorized users from uploading or modifying workflow files
- Deploy web application firewall (WAF) rules to detect and block XOML injection attempts
🔍 How to Verify
Check if Vulnerable:
Check if .NET Framework version is within affected ranges and if January 2020 security update is not installedCheck Version:
reg query "HKLM\SOFTWARE\Microsoft\NET Framework Setup\NDP\v4\Full" /v ReleaseVerify Fix Applied:
Verify that the January 2020 .NET Framework security update is installed via Windows Update history or system information📡 Detection & Monitoring
Log Indicators:
- Unusual XOML file uploads to SharePoint
- Failed workflow processing attempts
- Suspicious PowerShell or command execution from SharePoint processes
Network Indicators:
- Unusual outbound connections from SharePoint servers
- Traffic patterns indicating data exfiltration
SIEM Query:
source="sharepoint" AND (event="workflow_error" OR event="file_upload") AND file_extension="xoml"🔗 References
- http://packetstormsecurity.com/files/156930/SharePoint-Workflows-XOML-Injection.html
- https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2020-0646
- http://packetstormsecurity.com/files/156930/SharePoint-Workflows-XOML-Injection.html
- https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2020-0646
- https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2020-0646
