CVE-2021-31172
📋 TL;DR
CVE-2021-31172 is a spoofing vulnerability in Microsoft SharePoint Server that allows an attacker to trick users into performing actions they didn't intend. This affects organizations running vulnerable SharePoint Server versions, potentially leading to unauthorized actions or data exposure.
💻 Affected Systems
- Microsoft SharePoint Server
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
An attacker could impersonate legitimate users to perform administrative actions, modify content, or access sensitive data without authorization.
Likely Case
Attackers trick users into clicking malicious links that appear legitimate, leading to unintended actions within SharePoint.
If Mitigated
With proper authentication controls and user awareness, impact is limited to low-privilege actions by authenticated users.
🎯 Exploit Status
Exploitation requires user interaction and some level of access to SharePoint.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: May 2021 Security Updates
Vendor Advisory: https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-31172
Restart Required: Yes
Instructions:
1. Download the May 2021 security update for your SharePoint version from Microsoft Update Catalog. 2. Apply the update to all SharePoint servers. 3. Restart SharePoint services. 4. Test functionality.
🔧 Temporary Workarounds
Disable custom code
windowsRestrict or disable custom code execution in SharePoint to reduce attack surface.
🧯 If You Can't Patch
- Implement strict access controls and least privilege principles for SharePoint users.
- Enable detailed logging and monitoring for suspicious SharePoint activities.
🔍 How to Verify
Check if Vulnerable:
Check SharePoint Server version and compare with patched versions in Microsoft advisory.Check Version:
Get-SPFarm | Select BuildVersionVerify Fix Applied:
Verify that May 2021 security updates are installed via Windows Update or version check.📡 Detection & Monitoring
Log Indicators:
- Unusual authentication patterns
- Suspicious URL requests in SharePoint logs
- Unexpected user actions
Network Indicators:
- Abnormal traffic patterns to SharePoint web services
SIEM Query:
source="sharepoint" AND (url="*spoof*" OR action="unexpected")