---
id: "CVE-2026-45659"
kind: "vulnerability"
aliases: ["CVE-2026-45659"]
title: "microsoft sharepoint server: Deserialization of untrusted data in Microsoft Office SharePoint allows an authorized attacker to execute code over\u2026"
severity: "high"
cvss: 8.8
epss: null
exploited: true
status: "open"
category: "vendor"
products: [{"name": "microsoft sharepoint server", "fixed": ["16.0.19725.20280"], "affected": "< 16.0.19725.20280", "ecosystem": "vendor"}, {"name": "microsoft sharepoint server", "fixed": [], "affected": "= 2016", "ecosystem": "vendor"}, {"name": "microsoft sharepoint server", "fixed": [], "affected": "= 2019", "ecosystem": "vendor"}, {"name": "Microsoft SharePoint Server", "fixed": [], "affected": "", "ecosystem": "vendor"}]
ecosystems: ["vendor"]
tags: ["exploited", "ransomware", "self-hosted", "sharepoint-server", "vendor", "windows"]
not_affected_if: ["managed-hosting", "sharepoint-online"]
published_at: "2026-05-22T23:16:56+00:00"
first_seen_at: "2026-10-23T19:11:51+00:00"
updated_at: "2026-10-24T00:09:50+00:00"
sources: [{"source": "kev", "url": "https://www.cisa.gov/known-exploited-vulnerabilities-catalog?search_api_fulltext=CVE-2026-45659", "first_seen_at": "2026-10-23T19:11:51+00:00"}, {"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-45659", "first_seen_at": "2026-10-23T23:44:51+00:00"}]
---

# microsoft sharepoint server: Deserialization of untrusted data in Microsoft Office SharePoint allows an authorized attacker to execute code over…

Microsoft SharePoint Server has a deserialization of untrusted data flaw that lets an authorized attacker run code over the network. CISA lists it as actively exploited, with ransomware use noted in the tags.

_Summary, check and fix written by a model from the sources; labelled as such._

## Affected

- vendor:microsoft sharepoint server affected < 16.0.19725.20280 fixed 16.0.19725.20280
- vendor:microsoft sharepoint server affected = 2016 fixed ?
- vendor:microsoft sharepoint server affected = 2019 fixed ?
- vendor:Microsoft SharePoint Server affected ? fixed ?

## How to check

Identify SharePoint Server instances in your environment and confirm their build against Microsoft's security update guide for CVE-2026-45659; the sources do not give a specific build number or command.

## Fix

Apply the Microsoft SharePoint Server security update for CVE-2026-45659, or the vendor mitigation if no patch is available; the sources do not name the fixed version. If mitigations are unavailable, discontinue use of the product per CISA guidance.

## Timeline

- 2026-10-23T19:11:51+00:00 kev https://www.cisa.gov/known-exploited-vulnerabilities-catalog?search_api_fulltext=CVE-2026-45659
- 2026-10-23T23:44:51+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-45659

## From the sources

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

CISA 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.

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_Free to read at a human pace. An API with keys and an MCP server are in preparation; early access: hello@infrastack.ai_