CVE-2026-63516 in SharePoint Server
Summary
by MITRE • 08/11/2026
Deserialization of untrusted data in Microsoft Office SharePoint allows an authorized attacker to perform spoofing over a network.
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Analysis
by VulDB Data Team • 08/11/2026
This vulnerability represents a critical deserialization flaw within Microsoft Office SharePoint that enables authenticated attackers to manipulate serialized data structures and execute malicious operations. The core issue stems from insufficient validation of user-supplied data during the deserialization process, allowing adversaries to craft specially crafted payloads that can be interpreted and executed by the vulnerable system. When SharePoint processes untrusted serialized objects, it fails to properly sanitize or validate the incoming data, creating an attack surface where malicious inputs can be transformed into unauthorized actions. The vulnerability specifically enables network-based spoofing operations, which means attackers can potentially impersonate legitimate users or systems within the SharePoint environment.
The technical implementation of this flaw typically involves exploiting the way SharePoint handles serialized data formats such as xml or binary objects that are commonly used for storing and transmitting application state information. When an authenticated user submits data that gets processed through a deserialization routine, the system does not adequately verify the integrity or legitimacy of the serialized content before executing it. This creates opportunities for attackers to inject malicious code or manipulate object states that should remain protected, potentially allowing them to escalate privileges or redirect network traffic. The vulnerability operates at the application layer and can be particularly dangerous because it leverages existing authentication mechanisms rather than requiring additional access credentials.
The operational impact of this deserialization vulnerability extends beyond simple spoofing operations to encompass broader security implications within SharePoint environments. Attackers could potentially leverage this weakness to perform session hijacking, manipulate user permissions, or redirect traffic to malicious endpoints while maintaining the appearance of legitimate network activity. The authenticated nature of the attack means that adversaries do not need to compromise credentials through traditional means like brute force or credential theft, but can instead exploit existing access privileges. This makes the vulnerability particularly concerning for organizations where SharePoint serves as a central collaboration platform and where user authentication is already established.
Security practitioners should implement multiple layers of mitigation strategies to address this deserialization vulnerability. The primary approach involves strengthening input validation mechanisms within SharePoint applications to ensure that all serialized data undergoes rigorous integrity checks before processing. Organizations should also consider implementing strict access controls and monitoring for unusual deserialization patterns that might indicate exploitation attempts. Network segmentation and application-level firewalls can provide additional protection by limiting the attack surface and detecting anomalous traffic patterns associated with spoofing operations. This vulnerability aligns with CWE-502 which specifically addresses deserialization of untrusted data, and represents a potential entry point for attackers following ATT&CK techniques related to privilege escalation and lateral movement within network environments. Regular security updates and patches from Microsoft should be prioritized, along with comprehensive testing of application components that handle serialized data to prevent exploitation attempts.
The broader implications of this vulnerability highlight the importance of secure coding practices in enterprise collaboration platforms where user interaction with system components is common. SharePoint environments often store sensitive organizational information and facilitate complex workflows, making them attractive targets for sophisticated attacks that exploit subtle implementation flaws. The combination of authentication requirements and deserialization weaknesses creates a dangerous scenario where attackers can leverage legitimate access to perform operations that should remain restricted. Organizations must also consider implementing robust logging and monitoring solutions that can detect when serialized data is being processed in ways that deviate from expected patterns, providing early warning capabilities for potential exploitation attempts.