Microsoft SharePoint Server Deserialization of Untrusted Data Vulnerability

[ Why it matters ]Priority signals

• Exploited in the wild: on CISA's Known Exploited Vulnerabilities list since 2026-07-01
• Known to be used in ransomware campaigns

[ Description ]Official description

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

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

[ Fixes ]Fixes and patches

CISA required action (US federal deadline 4 Jul 2026): 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.

No fix or interim patch is linked from our sources yet. Check the vendor references below and limit exposure of affected systems until a fix is available.

[ References ]References

• msrc.microsoft.com/update-guide/vulnerability/CVE-2026-45659Vendor Advisory
• www.cisa.gov/known-exploited-vulnerabilities-catalogUS Government Resource