Microsoft SharePoint Server Deserialization of Untrusted Data Vulnerability

Summary

Microsoft SharePoint Server contains a deserialization of untrusted data vulnerability which allows an authorized attacker to execute code over a network.

Why it matters

CVE-2026-45659 is listed in CISA's Known Exploited Vulnerabilities catalog, confirming active exploitation in the wild. CISA remediation deadline: 2026-07-04. Treat remediation as urgent.

Operator check

Apply mitigations in accordance with vendor instructions, ensuring compliance with CISA’s BOD 26-04 Prioritizing Security Updates Based on Risk (see URL in Notes) guidance and CISA’s “Forensics Triage Requirements” (see URL in Notes). Follow applicable BOD 26-04 guidance for cloud services or discontinue use of the product if mitigations are unavailable. Stakeholders are responsible for evaluating each asset's internet exposure and ensuring adherence to BOD 26-04 patching guidelines.

Sources