CVE-2023-36891
📋 TL;DR
This vulnerability allows an attacker to inject malicious scripts into Microsoft SharePoint Server, which could execute when viewed by other users. It affects organizations running vulnerable SharePoint Server versions, potentially enabling cross-site scripting attacks.
💻 Affected Systems
- Microsoft SharePoint Server
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
An attacker could steal session cookies, redirect users to malicious sites, or perform actions on behalf of authenticated users, potentially leading to data theft or account compromise.
Likely Case
Attackers would typically use this to steal user credentials or session tokens, enabling unauthorized access to SharePoint content and functionality.
If Mitigated
With proper input validation and output encoding controls, the risk is significantly reduced, though patching remains essential.
🎯 Exploit Status
Exploitation typically requires some level of user interaction or access to inject malicious content.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Check Microsoft's monthly security updates for SharePoint Server
Vendor Advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2023-36891
Restart Required: Yes
Instructions:
1. Apply the latest security update from Microsoft's Patch Tuesday releases. 2. Restart SharePoint services. 3. Verify the update was successful.
🔧 Temporary Workarounds
Input Validation Enhancement
windowsImplement strict input validation and output encoding for user-supplied content in SharePoint.
🧯 If You Can't Patch
- Restrict user permissions to minimize who can post content to SharePoint.
- Implement web application firewall (WAF) rules to block common XSS payloads.
🔍 How to Verify
Check if Vulnerable:
Check SharePoint Server version against Microsoft's security bulletin for CVE-2023-36891.Check Version:
In SharePoint Central Administration, navigate to 'Upgrade and Migration' > 'Check product and patch installation status'.Verify Fix Applied:
Verify that the SharePoint Server version is updated to a patched release as specified by Microsoft.📡 Detection & Monitoring
Log Indicators:
- Unusual POST requests to SharePoint pages with script-like content in parameters.
- Errors related to input validation failures in SharePoint logs.
Network Indicators:
- HTTP requests containing suspicious script tags or JavaScript in URL parameters or form data.
SIEM Query:
source="sharepoint_logs" AND (http_method="POST" AND (uri="*aspx*" OR uri="*ashx*") AND (content="*<script>*" OR content="*javascript:*"))