CVE-2026-45659
Microsoft SharePoint Server Deserialization of Untrusted Data Vulnerability
Does this matter?
Known to be exploited in the wild (CISA KEV, CISA remediation deadline 4 July 2026). Treat as an emergency change: patch or isolate now, then hunt for prior compromise.
Description
Deserialization of untrusted data in Microsoft Office SharePoint allows an authorized attacker to execute code over a network.
- CVSS 3.1
- 8.8 HIGHCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
- EPSS
- 80.24% probability · 100th percentile
- Public exploits
- None in Exploit-DB
- CISA KEV
- Listed 1 July 2026 · due 4 July 2026 · used in ransomware campaigns
- Weakness
- CWE-502
- Affected
- microsoft/sharepoint server
- Source
- secure@microsoft.com
EPSS moved from 2.7% on 24 September 2026 to 80.2% on 27 October 2026. The dashed line is the ten per cent mark our analysts treat as “patch before the next change window”.
CISA notes
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. https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-45659 ; BOD 26-04: https://www.cisa.gov/news-events/directives/bod-26-04-prioritizing-security-updates-based-risk ; Forensics Triage Requirements: https://www.cisa.gov/news-events/directives/bod-26-04-implementation-guidance-prioritizing-security-updates-based-risk ; https://nvd.nist.gov/vuln/detail/CVE-2026-45659
References
Source: NVD record, EPSS from FIRST.org, KEV from CISA, exploits from Exploit-DB. Refreshed daily. Download this record as JSON.