CVE-2025-53770 concerns a critical vulnerability related to the deserialization of untrusted data in Microsoft SharePoint Server on-premises. SharePoint is a widely used collaboration platform that allows organizations to share and manage content, knowledge, and applications. Given its central role in information management and its typical deployment within corporate networks, a severe vulnerability like the deserialization of untrusted data can have significant security implications.

Technical Summary

Details:
This vulnerability stems from how Microsoft SharePoint Server on-premises handles the deserialization of untrusted data. Deserialization is the process by which a byte stream is converted back into an object in memory. When an application deserializes data from an untrusted source without proper validation or sanitization, an attacker can craft malicious serialized data that, once deserialized, executes arbitrary code or performs unintended actions on the server.
The core issue lies in the application’s failure to:

• Validate data integrity/origin: The server accepts and processes serialized data without properly verifying its source or ensuring it has not been tampered with.
• Configure deserialization securely: The deserialization process may not be securely configured, allowing for the exploitation of gadget chains (sequences of legitimate code that can be chained together to perform malicious actions).

Attack Vector:
An attacker could send specially crafted malicious serialized data to a vulnerable endpoint within SharePoint. This could occur through various input vectors, including:

• API Endpoints: Exploiting exposed APIs that handle serialized data.
• Request Parameters: Injecting malicious serialized objects into HTTP request parameters or headers.
• File Uploads: Camouflaging malicious serialized data within seemingly legitimate files that are then processed by the server.

The vulnerability is particularly dangerous because the deserialization process often occurs within the context of the application, which typically operates with elevated privileges on the server.

Impact:
The primary impact of a successful untrusted data deserialization attack is the achievement of Remote Code Execution (RCE). An attacker can gain direct control over the SharePoint server. Consequences may include:

• Full server compromise: Obtaining SYSTEM-level or equivalent privileges on the SharePoint server, allowing the attacker to install programs, view, modify, or delete data, or create new accounts with full rights.
• Data breach: Accessing and exfiltrating sensitive information stored within SharePoint.
• Lateral movement: Using the compromised SharePoint server as a foothold to access other systems and resources within the corporate network.
• Operational disruption: Interrupting SharePoint services, causing downtime for critical collaboration and content management functions.
• Website defacement: Modifying SharePoint sites to display malicious or unwanted content.

Recommendations

• Apply patches immediately: Prioritize the installation of all security updates and patches available from Microsoft for on-premises SharePoint Server installations. These patches are critical to resolving CVE-2025-53770 and other potential vulnerabilities.
• Apply the principle of least privilege: Ensure that SharePoint service accounts and application pools operate with the minimum necessary privileges on the server and file system.
• Network segmentation: Isolate SharePoint servers in a dedicated and restricted network segment. Limit network access only to what is strictly necessary for legitimate users and applications.