CVE-2026-70321 in SharePoint Server
Summary
by MITRE • 08/12/2026
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 • 08/12/2026
This vulnerability represents a critical deserialization flaw that exists within Microsoft Office SharePoint platforms, enabling authenticated attackers to execute arbitrary code remotely through network-based attacks. The issue stems from the improper handling of untrusted data during the deserialization process, where SharePoint fails to adequately validate or sanitize input received from network connections. When an attacker successfully exploits this weakness, they can craft malicious serialized objects that, upon processing by the vulnerable SharePoint system, trigger unintended code execution on the target server.
The technical nature of this vulnerability aligns with common weakness enumerations such as CWE-502, which specifically addresses deserialization of untrusted data. This flaw operates at the application layer where SharePoint's deserialization mechanisms are designed to reconstruct objects from serialized formats, but without proper input validation controls. Attackers can leverage this by sending specially crafted serialized payloads that exploit the deserialization process to execute malicious code with the privileges of the SharePoint service account. The network-based execution capability means that attackers do not require physical access to the system, making this vulnerability particularly dangerous in enterprise environments where SharePoint systems are accessible over corporate networks.
The operational impact of this vulnerability extends beyond simple code execution, as it can enable attackers to gain persistent access to SharePoint environments and potentially escalate privileges to compromise entire network infrastructures. Attackers may leverage this weakness to establish backdoors, exfiltrate sensitive data, or use the compromised SharePoint instance as a launchpad for further attacks within the organization's network perimeter. The vulnerability affects SharePoint server versions that process serialized data from untrusted sources, making it particularly concerning for organizations with extensive SharePoint deployments that handle sensitive corporate information.
Mitigation strategies should prioritize immediate patching of affected SharePoint versions and implementation of network segmentation controls to limit access to SharePoint systems. Organizations should also deploy application whitelisting policies and configure SharePoint to restrict deserialization of untrusted data through proper input validation. Security monitoring should focus on detecting anomalous deserialization activities and unusual network traffic patterns that might indicate exploitation attempts. The vulnerability demonstrates the importance of following secure coding practices and implementing proper input validation as outlined in the OWASP Top Ten security principles, while also aligning with MITRE ATT&CK framework techniques related to exploitation of remote services and privilege escalation through compromised applications.