CVE-2026-45659
Published 2026-05-22 · Updated 2026-07-23 · Source secure@microsoft.com
Summary
CVE-2026-45659 is a high-severity (CVSS 8.8) vulnerability in Microsoft SharePoint Server. CISA added it to the Known Exploited Vulnerabilities catalog on July 1, 2026, which means exploitation in the wild has been confirmed; US federal agencies had to remediate it by July 4, 2026. CISA also lists it as known to be used in ransomware campaigns, so it should be prioritised accordingly. Microsoft has 391 vulnerabilities in the KEV catalog, 117 of them linked to ransomware.
All 391 known-exploited Microsoft vulnerabilities →Description
Deserialization of untrusted data in Microsoft Office SharePoint allows an authorized attacker to execute code over a network.
CVSS vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
CISA Known-Exploited Vulnerability
Product: Microsoft — SharePoint Server
Name: Microsoft SharePoint Server Deserialization of Untrusted Data Vulnerability
Date added: 2026-07-01 · Due: 2026-07-04
Required action: 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.