CVE-2021-31948
📋 TL;DR
This vulnerability allows an authenticated attacker to spoof content in Microsoft SharePoint Server, potentially tricking users into interacting with malicious content. It affects SharePoint Server 2019 and SharePoint Server Subscription Edition. Attackers must have authenticated access to the SharePoint site.
💻 Affected Systems
- Microsoft SharePoint Server 2019
- Microsoft SharePoint Server Subscription Edition
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
An attacker could create convincing phishing pages within SharePoint that appear legitimate, leading to credential theft, malware installation, or data exfiltration when users interact with the spoofed content.
Likely Case
Attackers with authenticated access could create deceptive pages or content that misleads other SharePoint users, potentially leading to social engineering attacks or unauthorized actions.
If Mitigated
With proper authentication controls and user awareness training, the impact is limited to authenticated users who can already access the SharePoint environment.
🎯 Exploit Status
Exploitation requires authenticated access to SharePoint with content creation/modification permissions.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Security updates released in June 2021 (specific KB numbers vary by SharePoint version)
Vendor Advisory: https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-31948
Restart Required: Yes
Instructions:
1. Download the appropriate security update from Microsoft Update Catalog. 2. Apply the update to all SharePoint servers. 3. Restart SharePoint services or the server as required. 4. Test functionality after patching.
🔧 Temporary Workarounds
Restrict Content Creation Permissions
allLimit which users can create or modify SharePoint content to reduce attack surface
🧯 If You Can't Patch
- Implement strict access controls to limit who can create/modify SharePoint content
- Enable detailed auditing of SharePoint content creation and modification activities
🔍 How to Verify
Check if Vulnerable:
Check SharePoint Server version and compare against patched versions from June 2021 security updatesCheck Version:
Get-SPFarm | Select BuildVersion (PowerShell on SharePoint server)Verify Fix Applied:
Verify SharePoint Server has June 2021 security updates installed and version matches patched release📡 Detection & Monitoring
Log Indicators:
- Unusual content creation/modification patterns
- Multiple content changes from single user in short timeframe
Network Indicators:
- Unusual SharePoint content access patterns
SIEM Query:
source="SharePoint" AND (event="Content Created" OR event="Content Modified") AND user NOT IN [approved_content_creators]