CVE-2020-1595
📋 TL;DR
CVE-2020-1595 is a critical remote code execution vulnerability in Microsoft SharePoint where improperly protected APIs allow attackers to execute arbitrary code by sending specially-formatted input. Successful exploitation gives attackers full control over the SharePoint application pool and server farm account. Organizations running affected SharePoint versions with internet-facing or internal SharePoint servers are at risk.
💻 Affected Systems
- Microsoft SharePoint Server
- Microsoft SharePoint Foundation
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Complete compromise of SharePoint server farm, allowing attacker to execute arbitrary code with SharePoint application pool privileges, potentially leading to data theft, lateral movement, and full domain compromise.
Likely Case
Attacker gains control of SharePoint server, accesses sensitive data, and uses compromised server as foothold for further attacks within the network.
If Mitigated
With proper network segmentation and access controls, impact limited to SharePoint environment only, preventing lateral movement to other systems.
🎯 Exploit Status
Exploitation requires authenticated access to SharePoint API endpoints. Proof-of-concept code has been publicly released.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Apply Microsoft security updates from September 2020 or later
Vendor Advisory: https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2020-1595
Restart Required: Yes
Instructions:
1. Download and install the September 2020 security update for SharePoint from Microsoft Update Catalog. 2. Apply the update to all SharePoint servers in the farm. 3. Restart SharePoint services or reboot servers as required. 4. Test SharePoint functionality after patching.
🔧 Temporary Workarounds
Restrict API Access
windowsLimit access to SharePoint API endpoints using network firewalls or SharePoint permissions
Implement WAF Rules
allConfigure web application firewall to block suspicious deserialization patterns
🧯 If You Can't Patch
- Isolate SharePoint servers in separate network segments with strict firewall rules
- Implement strict access controls and monitor all API access attempts
🔍 How to Verify
Check if Vulnerable:
Check SharePoint version and patch level. If running affected versions without September 2020 security updates, system is vulnerable.Check Version:
Get-SPFarm | Select BuildVersion in SharePoint PowerShellVerify Fix Applied:
Verify SharePoint version shows September 2020 or later security updates installed. Test API endpoints for proper input validation.📡 Detection & Monitoring
Log Indicators:
- Unusual API access patterns
- Failed deserialization attempts in SharePoint logs
- Unexpected process execution from SharePoint application pool
Network Indicators:
- Unusual traffic to SharePoint API endpoints
- Suspicious deserialization payloads in HTTP requests
SIEM Query:
source="sharepoint*" AND ("deserialization" OR "api" AND "error") AND NOT status=200