Microsoft SharePoint Server Deserialization of Untrusted Data Vulnerability (CVE-2026-45659)
Severity: high · Patch status: unknown · Since 2026-07-01 · CVE-2026-45659
Microsoft SharePoint Server contains a deserialization of untrusted data vulnerability which allows an authorized attacker to execute code over a network. CISA added CVE-2026-45659 to its Known Exploited Vulnerabilities catalog on Jul 1, 2026, which means attackers are exploiting it in the wild. CISA reports known use in ransomware campaigns.
What to do
- 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.
- US federal agencies must remediate by Jul 4, 2026 (BOD 22-01); treat that as the outer limit.
Sources
All live incidents on Threat Watch
