CVE-2019-1203
📋 TL;DR
This is a cross-site scripting (XSS) vulnerability in Microsoft SharePoint Server that allows authenticated attackers to inject malicious scripts into web pages. When exploited, these scripts execute with the victim's permissions, potentially enabling unauthorized data access, content manipulation, or account takeover. 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 attacker could gain administrative privileges, exfiltrate sensitive data, delete or modify all SharePoint content, and maintain persistent access through backdoors.
Likely Case
Attackers would steal session cookies, perform actions as authenticated users (like changing permissions or deleting documents), and potentially access sensitive information within the user's authorization scope.
If Mitigated
With proper input validation and output encoding, the impact is limited to failed exploitation attempts with no compromise.
🎯 Exploit Status
Exploitation requires authenticated access to SharePoint and knowledge of vulnerable endpoints. XSS vulnerabilities are commonly exploited once details are known.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Security updates released in August 2019 patches
Vendor Advisory: https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2019-1203
Restart Required: Yes
Instructions:
1. Download the appropriate security update from Microsoft Update Catalog. 2. Apply the update to all affected SharePoint servers. 3. Restart the SharePoint servers and services. 4. Test functionality after patching.
🔧 Temporary Workarounds
Input Validation Enhancement
windowsImplement additional input validation and output encoding for SharePoint web requests
Content Security Policy
allImplement strict Content Security Policy headers to mitigate XSS impact
🧯 If You Can't Patch
- Implement web application firewall (WAF) rules to block XSS payloads
- Restrict SharePoint access to only necessary users and monitor for suspicious activity
🔍 How to Verify
Check if Vulnerable:
Check SharePoint Server version and compare against patched versions from Microsoft's August 2019 security updatesCheck Version:
Get-SPFarm | Select BuildVersion (PowerShell) or check Central Administration > Upgrade and Migration > Check product and patch installation statusVerify Fix Applied:
Verify that the security update is installed via Windows Update history or SharePoint version check📡 Detection & Monitoring
Log Indicators:
- Unusual POST requests to SharePoint endpoints with script-like payloads
- Multiple failed authentication attempts followed by successful login and suspicious requests
Network Indicators:
- HTTP requests containing JavaScript or HTML injection patterns to SharePoint URLs
SIEM Query:
source="sharepoint_logs" AND (uri="*<script*" OR uri="*javascript:*" OR uri="*onerror=*" OR uri="*onload=*")