CVE-2020-1482
📋 TL;DR
This is a cross-site scripting (XSS) vulnerability in Microsoft SharePoint Server where improper input sanitization allows authenticated attackers to inject malicious scripts. Successful exploitation enables attackers to perform actions as the victim user, including reading unauthorized content, modifying permissions, deleting data, and injecting malicious content into browsers. Only authenticated users can exploit this vulnerability against affected SharePoint servers.
💻 Affected Systems
- Microsoft SharePoint Server
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
An authenticated attacker could gain administrative privileges, exfiltrate sensitive data, delete or modify all SharePoint content, and maintain persistent access through backdoors.
Likely Case
Authenticated users with limited privileges could escalate their permissions, access sensitive documents they shouldn't see, and perform actions like deleting content or changing permissions on behalf of other users.
If Mitigated
With proper input validation and output encoding controls, the risk is reduced to minimal, though the vulnerability still exists in unpatched systems.
🎯 Exploit Status
Exploitation requires authenticated access to SharePoint; XSS vulnerabilities are commonly exploited and weaponization is likely
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Specific patch version available through Microsoft Security Update
Vendor Advisory: https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2020-1482
Restart Required: Yes
Instructions:
1. Download the security update from Microsoft Update Catalog. 2. Apply the update to affected SharePoint servers. 3. Restart SharePoint services or the server as required. 4. Test functionality after patching.
🔧 Temporary Workarounds
Implement Content Security Policy (CSP)
windowsAdd Content Security Policy headers to restrict script execution sources
Add 'Content-Security-Policy' header to SharePoint web.config or IIS settings
Input Validation Controls
allImplement additional input validation and output encoding in custom SharePoint solutions
Review and update custom web parts and solutions to implement proper input sanitization
🧯 If You Can't Patch
- Restrict SharePoint access to trusted users only and implement strict authentication controls
- Implement web application firewall (WAF) rules to detect and block XSS payloads
🔍 How to Verify
Check if Vulnerable:
Check SharePoint version against Microsoft Security Update guide; test for XSS vulnerabilities using authorized penetration testingCheck Version:
Get-SPFarm | Select BuildVersion (PowerShell on SharePoint server)Verify Fix Applied:
Verify patch installation through Windows Update history; test XSS payloads to confirm sanitization📡 Detection & Monitoring
Log Indicators:
- Unusual POST requests with script tags or JavaScript payloads in query parameters
- Multiple failed authentication attempts followed by successful login and suspicious requests
Network Indicators:
- HTTP requests containing <script> tags or JavaScript in parameters
- Unusual outbound connections from SharePoint servers
SIEM Query:
source="sharepoint" AND (http_request="*<script>*" OR http_request="*javascript:*" OR http_request="*onload=*" OR http_request="*onerror=*")