CVE-2026-65663 in SharePoint Server
Summary
by MITRE • 08/11/2026
Deserialization of untrusted data in Microsoft Office SharePoint allows an authorized attacker to execute code over a network.
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Analysis
by VulDB Data Team • 08/11/2026
This vulnerability represents a critical deserialization flaw that exists within Microsoft Office SharePoint platforms, specifically targeting the handling of untrusted data inputs. The weakness occurs when the system processes serialized data from external sources without proper validation or sanitization measures, creating an environment where malicious actors can exploit this gap to execute arbitrary code remotely. The vulnerability is particularly dangerous because it requires only authorized access to the SharePoint environment, meaning that attackers who have legitimate user credentials can leverage this flaw to escalate their privileges and gain unauthorized system control. According to CWE classification, this scenario aligns with CWE-502 which describes unsafe deserialization vulnerabilities where untrusted data is deserialized without proper validation, leading to potential remote code execution. The attack vector typically involves crafting malicious serialized objects that when processed by the SharePoint server will trigger unintended code execution.
The technical implementation of this vulnerability allows attackers to manipulate serialized data structures that are normally used for transferring objects between different parts of an application or system. When SharePoint processes these serialized objects, it fails to validate the integrity or content of the data before deserializing it into executable code. This flaw can be exploited through various attack surfaces within SharePoint including web services, file upload mechanisms, and user input fields that accept serialized data. The operational impact is severe as successful exploitation can result in complete system compromise, allowing attackers to execute commands with the privileges of the SharePoint service account, potentially leading to full network infiltration and data exfiltration capabilities.
From a threat modeling perspective, this vulnerability maps directly to several ATT&CK techniques including T1059 for command and scripting interpreter and T1078 for valid accounts, as attackers can leverage legitimate user credentials to perform exploitation. The attack chain typically begins with an authenticated user session, followed by the delivery of malicious serialized data through SharePoint's web interface or APIs, and concludes with remote code execution on the server. Organizations running SharePoint environments are particularly vulnerable because the platform's architecture relies heavily on data serialization for various functions including caching, session management, and cross-component communication. The remediation strategy requires immediate implementation of input validation controls, disabling unnecessary deserialization capabilities, and implementing proper security boundaries between different components of the SharePoint infrastructure.
Security hardening measures should focus on restricting deserialization operations to only trusted sources and implementing strict validation of serialized data before processing. Organizations must also consider deploying web application firewalls that can detect and block suspicious deserialization patterns, along with regular security assessments to identify and remediate similar vulnerabilities throughout the SharePoint ecosystem. The vulnerability demonstrates how modern enterprise applications can become attack vectors when proper input sanitization controls are not implemented, making it essential for security teams to understand both the technical implementation details and broader implications of such flaws in their defensive strategies.