CVE-2025-29793: SharePoint Enterprise Server RCE Vulnerability

CVE-2025-29793 Overview

CVE-2025-29793 is a high-severity insecure deserialization vulnerability in Microsoft Office SharePoint that allows an authorized attacker to execute arbitrary code over a network. This vulnerability stems from the improper handling of serialized data within SharePoint, enabling attackers with authenticated access to craft malicious payloads that are processed by the server without adequate validation.

Critical Impact

Authenticated attackers can achieve remote code execution on SharePoint servers, potentially compromising confidential data, modifying content, and disrupting critical collaboration services across enterprise environments.

Affected Products

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

Discovery Timeline

• April 8, 2025 - CVE-2025-29793 published to NVD
• July 9, 2025 - Last updated in NVD database

Technical Details for CVE-2025-29793

Vulnerability Analysis

This vulnerability is classified under CWE-502 (Deserialization of Untrusted Data), a well-documented weakness category that has historically led to severe security breaches in enterprise applications. SharePoint's architecture relies heavily on serialization for data exchange and state management, making it particularly susceptible to this class of vulnerabilities when input validation is insufficient.

The attack requires the adversary to possess valid credentials with some level of privilege on the target SharePoint instance. Once authenticated, the attacker can submit specially crafted serialized objects through SharePoint's network-accessible interfaces. When the server deserializes these malicious objects, it inadvertently executes attacker-controlled code within the context of the SharePoint application process.

The successful exploitation of this vulnerability could result in complete compromise of data confidentiality, integrity, and availability on the affected SharePoint server. Attackers could exfiltrate sensitive documents, inject malicious content, establish persistence mechanisms, or pivot to other systems within the network.

Root Cause

The root cause of CVE-2025-29793 lies in SharePoint's failure to adequately validate and sanitize serialized data before processing. When the application accepts serialized objects from authenticated users without verifying the object types or contents against a strict allowlist, it creates an opportunity for attackers to inject malicious objects. These objects, when deserialized, can trigger arbitrary code execution through gadget chains present in the application's class library dependencies.

Attack Vector

The attack is executed over the network and requires the attacker to have authenticated access to the SharePoint instance. The attacker crafts a malicious serialized payload containing objects that, when deserialized, chain together to execute arbitrary commands or code. This payload is submitted through SharePoint's web services or API endpoints that process serialized data.

The attack does not require user interaction once the attacker has obtained valid credentials. The exploitation complexity is relatively low given the well-documented nature of .NET deserialization attacks and the availability of tools for generating malicious payloads. Organizations should assume that any authenticated user with network access to SharePoint could potentially exploit this vulnerability.

For detailed technical information regarding this vulnerability, refer to the Microsoft Security Update for CVE-2025-29793.

Detection Methods for CVE-2025-29793

Indicators of Compromise

• Unusual serialized object payloads in HTTP POST requests to SharePoint endpoints containing suspicious class names or gadget chain signatures
• Unexpected process spawning from SharePoint application pool worker processes (w3wp.exe)
• Anomalous outbound network connections originating from SharePoint servers
• Creation of unauthorized files or modifications to SharePoint configuration files

Detection Strategies

• Monitor web server logs for suspicious POST requests with abnormally large or encoded payloads targeting SharePoint web services
• Deploy YARA rules to detect known .NET deserialization gadget chains in network traffic
• Implement endpoint detection rules to alert on w3wp.exe spawning child processes such as cmd.exe, powershell.exe, or certutil.exe
• Analyze Windows Security Event Logs for process creation events (Event ID 4688) associated with SharePoint application pools

Monitoring Recommendations

• Enable verbose logging on SharePoint servers and forward logs to a centralized SIEM for correlation
• Implement network segmentation and monitor traffic flows to and from SharePoint servers for anomalies
• Deploy file integrity monitoring on SharePoint installation directories and web root folders
• Establish baseline behavior for SharePoint application pools and alert on deviations

How to Mitigate CVE-2025-29793

Immediate Actions Required

• Apply the latest security updates from Microsoft for affected SharePoint versions immediately
• Review and restrict authenticated user permissions to the minimum necessary for their roles
• Implement network segmentation to limit access to SharePoint servers from untrusted network zones
• Enable enhanced audit logging on SharePoint servers to facilitate incident detection and response

Patch Information

Microsoft has released security updates addressing CVE-2025-29793 for all affected SharePoint versions. Organizations should prioritize patch deployment given the network-accessible nature of the vulnerability and its potential impact. Detailed patch information and download links are available in the Microsoft Security Update for CVE-2025-29793.

Workarounds

• Restrict network access to SharePoint servers using firewall rules, limiting connections to trusted IP ranges only
• Implement Web Application Firewall (WAF) rules to inspect and block suspicious serialized payloads targeting SharePoint endpoints
• Consider temporarily disabling non-essential SharePoint web services and APIs until patches can be applied
• Enforce multi-factor authentication for all SharePoint users to reduce the risk of credential compromise

# Example: Restrict SharePoint access at the firewall level
# Allow only trusted corporate network ranges
netsh advfirewall firewall add rule name="SharePoint Trusted Access" dir=in action=allow protocol=tcp localport=443 remoteip=10.0.0.0/8,172.16.0.0/12,192.168.0.0/16

# Block all other inbound connections to SharePoint ports
netsh advfirewall firewall add rule name="SharePoint Block External" dir=in action=block protocol=tcp localport=443 remoteip=any