CVE-2026-65658 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, enabling authenticated attackers to perform remote code execution through maliciously crafted data payloads. The issue stems from the application's insufficient validation mechanisms when processing serialized objects, particularly those originating from untrusted sources such as user input or external data streams. When SharePoint encounters serialized data during normal operations, it fails to adequately sanitize or verify the integrity of these objects before deserializing them into executable code within the application's memory space. This weakness creates a direct pathway for attackers who have already established authentication credentials to escalate their privileges and execute arbitrary commands on the target system.
The technical exploitation occurs when an attacker leverages their authenticated access to upload or manipulate serialized data structures that contain malicious code within SharePoint's processing pipeline. During deserialization, the application interprets these crafted payloads as legitimate instructions rather than potentially harmful code constructs. This vulnerability can be exploited through various attack vectors including document uploads, web service calls, or API interactions where user-supplied data flows into the deserialization logic. The flaw aligns with common weakness enumerations such as CWE-502 which specifically addresses deserialization of untrusted data, and represents a significant risk in enterprise environments where SharePoint serves as a central collaboration platform for business operations.
The operational impact of this vulnerability extends beyond simple privilege escalation to encompass complete system compromise and potential lateral movement within network infrastructures. An attacker who successfully exploits this weakness can execute commands with the privileges of the SharePoint service account, potentially leading to data exfiltration, persistent backdoor installation, or further exploitation of interconnected systems. The attack surface is particularly concerning in environments where SharePoint integrates with other Microsoft products such as Exchange, Active Directory, or SQL Server, as successful exploitation could enable attackers to pivot across these integrated platforms. This vulnerability directly maps to several ATT&CK techniques including T1059 for command and script interpreter execution, and T1078 for valid accounts usage, making it a particularly dangerous threat vector for enterprise security postures.
Organizations should implement multiple layers of defense to mitigate this risk, beginning with immediate patching of affected SharePoint versions and ensuring proper network segmentation between SharePoint servers and critical infrastructure components. Regular monitoring of deserialization activities within SharePoint logs can help identify potential exploitation attempts before they succeed. Security teams should also implement strict input validation controls, disable unnecessary deserialization features, and consider implementing application whitelisting policies to restrict execution of unsigned code. Additionally, organizations should conduct regular security assessments targeting SharePoint environments and ensure that proper access controls are in place to limit the scope of potential exploitation, particularly focusing on limiting administrative privileges for SharePoint service accounts and implementing principle of least privilege configurations across all integrated systems.