CVE-2025-47166: SharePoint Enterprise Server RCE Vulnerability

CVE-2025-47166 Overview

CVE-2025-47166 is a high-severity insecure deserialization vulnerability affecting Microsoft Office SharePoint that enables an authorized attacker to execute arbitrary code over a network. The vulnerability stems from improper handling of untrusted data during deserialization operations within SharePoint, classified under CWE-502 (Deserialization of Untrusted Data).

This vulnerability allows authenticated users with network access to SharePoint servers to leverage malicious serialized objects to achieve remote code execution. Given SharePoint's widespread deployment in enterprise environments for document management and collaboration, successful exploitation could lead to significant compromise of sensitive corporate data and infrastructure.

Critical Impact

Authenticated attackers can achieve remote code execution on vulnerable SharePoint servers, potentially compromising enterprise collaboration infrastructure and sensitive organizational data.

Affected Products

• Microsoft SharePoint Enterprise Server 2016
• Microsoft SharePoint Server 2019
• Microsoft SharePoint Server Subscription Edition

Discovery Timeline

• June 10, 2025 - CVE-2025-47166 published to NVD
• July 9, 2025 - Last updated in NVD database

Technical Details for CVE-2025-47166

Vulnerability Analysis

This insecure deserialization vulnerability affects the core data processing mechanisms within Microsoft SharePoint. Deserialization vulnerabilities occur when applications reconstruct objects from serialized data without proper validation, allowing attackers to manipulate the serialized data stream to inject malicious objects or code.

In the context of SharePoint, authenticated users can submit specially crafted serialized payloads that are processed by the server. When SharePoint deserializes this untrusted input without adequate security controls, the attacker-controlled objects are instantiated, potentially triggering arbitrary code execution on the server.

The attack requires low privileges and can be executed over the network without user interaction, making it particularly dangerous in enterprise environments where SharePoint instances are accessible across corporate networks or potentially exposed to the internet.

Root Cause

The root cause of CVE-2025-47166 lies in insufficient validation of serialized data before deserialization operations. SharePoint fails to properly verify the integrity and safety of incoming serialized objects, allowing malicious payloads to be processed. This is a classic instance of CWE-502, where the application deserializes data from an untrusted source without implementing appropriate safeguards such as type whitelisting, integrity verification, or sandboxed deserialization.

Attack Vector

The attack vector is network-based, requiring the attacker to have authenticated access to the SharePoint environment. The exploitation flow typically involves:

1. An authenticated attacker crafts a malicious serialized object containing code execution payloads
2. The attacker submits this payload to a vulnerable SharePoint endpoint that processes serialized data
3. SharePoint deserializes the malicious object without proper validation
4. The deserialization process triggers the execution of attacker-controlled code with the privileges of the SharePoint application pool

The vulnerability can be exploited through various SharePoint features that handle serialized .NET objects, potentially including workflow processing, list operations, or web service endpoints.

Detection Methods for CVE-2025-47166

Indicators of Compromise

• Unusual serialized object submissions to SharePoint endpoints, particularly containing suspicious .NET type references
• Unexpected process spawning from w3wp.exe processes associated with SharePoint application pools
• Anomalous network connections originating from SharePoint servers
• Evidence of ysoserial.net or similar deserialization payload tools in logs or network traffic

Detection Strategies

• Monitor SharePoint ULS logs for deserialization-related errors or exceptions
• Implement network intrusion detection rules to identify known .NET deserialization payload patterns
• Deploy endpoint detection and response (EDR) solutions to detect suspicious process behaviors from IIS worker processes
• Review SharePoint audit logs for unusual user activities preceding potential exploitation attempts

Monitoring Recommendations

• Enable verbose logging on SharePoint servers and centralize logs for analysis
• Configure alerts for unusual process creation events from SharePoint-related processes
• Monitor for outbound connections from SharePoint servers to unexpected destinations
• Implement file integrity monitoring on SharePoint server directories

How to Mitigate CVE-2025-47166

Immediate Actions Required

• Apply the latest Microsoft security updates for affected SharePoint versions immediately
• Review SharePoint server access controls to ensure only necessary users have authenticated access
• Implement network segmentation to limit exposure of SharePoint servers
• Enable enhanced logging and monitoring to detect potential exploitation attempts

Patch Information

Microsoft has released security updates to address this vulnerability. Administrators should apply patches through Windows Update, Windows Server Update Services (WSUS), or download updates directly from the Microsoft Update Catalog. For detailed patch information and download links, refer to the Microsoft Security Update Guide for CVE-2025-47166.

Ensure that patches are applied to all affected SharePoint versions:

• SharePoint Enterprise Server 2016
• SharePoint Server 2019
• SharePoint Server Subscription Edition

Workarounds

• Restrict network access to SharePoint servers using firewalls and access control lists
• Implement web application firewall (WAF) rules to filter potentially malicious serialized payloads
• Review and limit user permissions to reduce the pool of potential attackers with authenticated access
• Consider temporarily disabling non-essential SharePoint features that may process serialized data until patches can be applied

# Example: Restrict SharePoint site access using IIS IP restrictions
# Add to applicationHost.config or configure via IIS Manager
# This limits access to trusted IP ranges only

# PowerShell example to review SharePoint farm configuration
Get-SPFarm | Select-Object BuildVersion, Status
Get-SPWebApplication | Get-SPSite | Select-Object Url, LastContentModifiedDate