CVE-2026-45659: Microsoft SharePoint Server Deserialization of Untrusted Data Vulnerability

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

VendorMicrosoft
ProductSharePoint Server
Date added to KEV2026-07-01
Due date (BOD 22-01)2026-07-04
Known ransomware campaign useKnown
CWECWE-502
Required actionApply 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.

What to do

  1. Identify every instance of Microsoft SharePoint Server in your environment (asset inventory, EDR, vulnerability scanner).
  2. Apply CISA's 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.
  3. Federal civilian agencies must act by 2026-07-04 under BOD 22-01; other organizations can use the same date as a target.
  4. Because ransomware use is known, check for signs of compromise and confirm backups are offline and tested.
  5. Check the vendor advisory and NVD entry linked below for affected versions, then record the fix in your change log.

This CVE is flagged by CISA as known to be used in ransomware campaigns. Rehearse your response before you need it: Ransomware tabletop exercise kit (Runbook Foundry).

Sources

Generated from the CISA feed with AI assistance; facts are taken verbatim from the feed. Not affiliated with or endorsed by CISA. Facts come from the CISA Known Exploited Vulnerabilities catalog (public domain).