CVE intelligenceCISA KEVRansomware use

CVE-2026-45659

Microsoft SharePoint Server Deserialization of Untrusted Data Vulnerability

Published May 22, 2026Sources checked Sep 27, 2026

8.8HIGHCVSS out of 10

What this means

Actively exploited

CISA lists CVE-2026-45659 in its Known Exploited Vulnerabilities catalog, which means exploitation has been observed. The entry applies to Microsoft SharePoint Server.

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.

CISA KEVListedObserved exploitation

EPSS2.7%Estimated 30-day exploitation probability

Ransomware useReported by CISACISA KEV ransomware field

Threat actors1Source-linked actor relationships

Overview

What is CVE-2026-45659?

Deserialization of untrusted data in Microsoft Office SharePoint allows an authorized attacker to execute code over a network.