CVE-2020-16951 in SharePoint Server
Summary
by MITRE • 10/17/2020
<p>A remote code execution vulnerability exists in Microsoft SharePoint when the software fails to check the source markup of an application package. An attacker who successfully exploited the vulnerability could run arbitrary code in the context of the SharePoint application pool and the SharePoint server farm account.</p> <p>Exploitation of this vulnerability requires that a user uploads a specially crafted SharePoint application package to an affected version of SharePoint.</p> <p>The security update addresses the vulnerability by correcting how SharePoint checks the source markup of application packages.</p>
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Analysis
by VulDB Data Team • 02/25/2026
This vulnerability represents a critical remote code execution flaw in Microsoft SharePoint systems that stems from inadequate validation of application package markup sources. The weakness exists within the SharePoint application's package handling mechanism where the system fails to properly verify the integrity and origin of application packages before processing them. This failure creates a pathway for attackers to execute malicious code with elevated privileges equivalent to those of the SharePoint application pool and server farm account. The vulnerability specifically targets the package validation process, which is a fundamental security control designed to prevent unauthorized software deployment and execution within the SharePoint environment.
The exploitation scenario requires a user interaction component where an attacker must successfully upload a maliciously crafted SharePoint application package to an affected system. This upload requirement places the vulnerability in the category of user-assisted remote code execution attacks, where social engineering or other means of gaining upload access become critical attack vectors. The attack chain begins with package creation, followed by upload to SharePoint, and concludes with automatic execution of malicious code within the SharePoint application context. The vulnerability is particularly concerning because it allows attackers to escalate privileges beyond normal user boundaries and potentially gain access to sensitive organizational data and infrastructure resources.
The technical impact of this vulnerability extends beyond simple code execution to encompass complete system compromise potential. When successfully exploited, the malicious code runs with the highest privileges available to the SharePoint application, which typically includes access to the underlying database and server resources. This privilege escalation capability enables attackers to perform actions such as data exfiltration, system modification, privilege escalation to domain administrator accounts, and establishment of persistent access points within the network. The vulnerability affects the core SharePoint application pool and server farm account contexts, which are typically configured with broad system access permissions, making the potential impact significantly more severe than typical user-level exploits.
Microsoft addressed this vulnerability through enhanced package validation mechanisms that properly verify the source markup of application packages before allowing them to be processed. The fix involves implementing stricter checks on package integrity and source verification, ensuring that only properly signed and verified packages can be deployed within SharePoint environments. This remediation aligns with security best practices outlined in the CWE (Common Weakness Enumeration) framework, specifically addressing weaknesses related to insufficient input validation and improper privilege management. Organizations should implement the security update immediately and conduct thorough testing to ensure compatibility with existing SharePoint deployments while maintaining the enhanced security controls.
The vulnerability demonstrates the importance of proper input validation and package integrity checking in enterprise collaboration platforms. From an ATT&CK framework perspective, this vulnerability maps to techniques involving package manipulation and privilege escalation within application environments. The exploit requires a user upload action, which aligns with initial access techniques that leverage user interaction to establish footholds within target environments. Security professionals should implement network monitoring for suspicious package upload activities and establish robust access controls to minimize the risk of unauthorized package deployment. Additionally, regular security assessments of SharePoint environments should include verification of package validation controls and monitoring for anomalous execution patterns that might indicate exploitation attempts.