---
id: "CVE-2026-56164"
kind: "vulnerability"
aliases: ["CVE-2026-56164"]
title: "microsoft sharepoint server: Missing authentication for critical function in Microsoft Office SharePoint allows an unauthorized attacker to\u2026"
severity: "critical"
cvss: 9.8
epss: null
exploited: true
status: "open"
category: "vendor"
products: [{"name": "microsoft sharepoint server", "fixed": ["16.0.19725.20434"], "affected": "< 16.0.19725.20434", "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", "self-hosted", "sharepoint-server", "vendor", "windows"]
not_affected_if: ["sharepoint-online"]
published_at: "2026-07-14T00:00:00+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-2026-56164", "first_seen_at": "2026-10-23T19:11:51+00:00"}, {"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-56164", "first_seen_at": "2026-10-23T23:44:51+00:00"}]
---

# microsoft sharepoint server: Missing authentication for critical function in Microsoft Office SharePoint allows an unauthorized attacker to…

Microsoft SharePoint Server has a missing authentication check on a critical function that lets an unauthenticated network attacker gain elevated privileges. CISA lists it as actively exploited in the wild.

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

## Affected

- vendor:microsoft sharepoint server affected < 16.0.19725.20434 fixed 16.0.19725.20434
- vendor:microsoft sharepoint server affected = 2016 fixed ?
- vendor:microsoft sharepoint server affected = 2019 fixed ?
- vendor:Microsoft SharePoint Server affected ? fixed ?

## Fix

Apply the Microsoft security update or mitigations for CVE-2026-56164 per vendor instructions and CISA BOD 26-04; if no mitigation exists, discontinue use of the product as CISA directs.

## Timeline

- 2026-10-23T19:11:51+00:00 kev https://www.cisa.gov/known-exploited-vulnerabilities-catalog?search_api_fulltext=CVE-2026-56164
- 2026-10-23T23:44:51+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-56164

## From the sources

Microsoft SharePoint contains a missing authentication for critical function vulnerability that allows an unauthorized attacker to elevate privileges 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_