CVE-2025-29793
📋 TL;DR
This vulnerability allows an authenticated attacker to execute arbitrary code on Microsoft SharePoint servers by exploiting insecure deserialization of untrusted data. It affects organizations running vulnerable SharePoint versions, requiring network access and valid credentials.
💻 Affected Systems
- Microsoft SharePoint Server
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Full server compromise leading to data theft, lateral movement, ransomware deployment, or complete SharePoint environment takeover.
Likely Case
Privilege escalation leading to unauthorized data access, configuration changes, or installation of backdoors.
If Mitigated
Limited impact due to network segmentation, strong authentication controls, and monitoring preventing successful exploitation.
🎯 Exploit Status
Requires authentication but deserialization vulnerabilities often have reliable exploitation paths once understood.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Will be specified in Microsoft's monthly security update
Vendor Advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2025-29793
Restart Required: Yes
Instructions:
1. Monitor Microsoft's Patch Tuesday updates
2. Apply SharePoint security updates through Windows Update or WSUS
3. Restart SharePoint services after patch installation
4. Test in non-production environment first
🔧 Temporary Workarounds
Restrict SharePoint network access
windowsLimit SharePoint server access to trusted networks only using firewall rules
New-NetFirewallRule -DisplayName "Block SharePoint External" -Direction Inbound -Protocol TCP -LocalPort 80,443 -RemoteAddress Internet -Action Block
Implement application whitelisting
windowsPrevent execution of unauthorized binaries that might be deployed via exploitation
🧯 If You Can't Patch
- Implement strict network segmentation to isolate SharePoint servers
- Enforce least privilege access controls and monitor for unusual authentication patterns
🔍 How to Verify
Check if Vulnerable:
Check SharePoint version against Microsoft's security bulletin once publishedCheck Version:
Get-SPFarm | Select BuildVersionVerify Fix Applied:
Verify SharePoint version matches patched version in Microsoft advisory📡 Detection & Monitoring
Log Indicators:
- Unusual deserialization errors in SharePoint logs
- Unexpected process creation from SharePoint worker processes
- Authentication from unusual locations followed by code execution attempts
Network Indicators:
- Unusual outbound connections from SharePoint servers
- HTTP requests containing serialized objects to SharePoint endpoints
SIEM Query:
source="sharepoint_logs" AND ("deserialization" OR "TypeLoadException" OR "SerializationException")