CVE-2026-45659
KEVRansomware UseMicrosoft SharePoint Server Deserialization of Untrusted Data Vulnerability
Description
Microsoft SharePoint Server contains a deserialization of untrusted data vulnerability which allows an authorized attacker to execute code over a network.
Deserialization of untrusted data in Microsoft Office SharePoint allows an authorized attacker to execute code over a network.
CVSS 3.1 vector
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:HPublishedMay 22, 2026
Last modifiedJul 23, 2026
Added to KEVJul 1, 2026
Remediation dueJul 4, 2026
References
- msrc.microsoft.com/update-guide/vulnerability/CVE-2026-45659Vendor Advisory
- cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2026-45659US Government Resource
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Risk assessment · Critical
Actively exploited and used by ransomware crews. Patch immediately.
- Exploitation
- Confirmed in the wild (CISA KEV)
- Federal remediation deadline
- Overdue by 114 days
- Ransomware
- Used in known ransomware campaigns
- CVSS
- 8.8 HIGH
- EPSS (30-day exploit probability)
- 80.2% · top 1% of all CVEs
- Weakness
- CWE-502
- Attack vector
- Network, remotely reachable
Recommended actions
- 1.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.
- 2.Treat as emergency change: patch or isolate internet-facing instances first.
- 3.Review exposure: confirm which instances are reachable from the internet and restrict access until patched.
- 4.Hunt for compromise: review logs for the disclosure window, not just from the patch date.
- 5.Verify offline/immutable backups and segment the affected systems. This flaw is used for ransomware initial access.
Assessment is derived automatically from the live signals above; verify against your own asset inventory.