---
id: CVE-2026-55040
title: Microsoft SharePoint Server Security Feature Bypass Vulnerability
summary: >-
  Weak authentication in Microsoft Office SharePoint allows an unauthorized
  attacker to bypass a security feature over a network.
severity: critical
cvss: 9.1
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N/E:U/RL:O/RC:C'
cvssSource: cna
cwe:
  - CWE-1390
vendor: Microsoft
product: Microsoft SharePoint Enterprise Server 2016
affected:
  - sharepoint_enterprise_server_2016 >= 16.0.0 < 16.0.5561.1001
  - sharepoint_server_2019 >= 16.0.0 < 16.0.10417.20175
  - sharepoint_server_subscription_edition >= 16.0.0 < 16.0.19725.20434
ssvc:
  exploitation: active
  automatable: 'yes'
  technicalImpact: total
  timestamp: '2026-07-13T00:00:00+00:00'
exploited: true
exploitAvailable: true
published: '2026-07-14'
updated: '2026-09-17'
sourceUpdated: '2026-09-17T22:32:59.741Z'
source: CVEORG
sourceUrl: 'https://www.cve.org/CVERecord?id=CVE-2026-55040'
references:
  - url: 'https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-55040'
    label: Microsoft SharePoint Server Security Feature Bypass Vulnerability
tags:
  - cve.org
  - in-the-wild
  - exploit-available
  - kev
epss: 0.50585
epssPercentile: 0.98896
kev: true
kevDateAdded: '2026-08-18'
kevDueDate: '2026-08-21'
kevRansomware: false
exploits:
  github: 5
  githubRepos:
    - 'https://github.com/sfewer-r7/CVE-2026-55040'
    - 'https://github.com/l0ggg/CVE-2026-55040'
    - 'https://github.com/zenzue/CVE-2026-55040'
  nuclei:
    - javascript/cves/2026/CVE-2026-55040
  checkedAt: '2026-09-21T15:29:33.426Z'
ingestedAt: '2026-09-08T17:06:31.908Z'
---

## Overview

Weak authentication in Microsoft Office SharePoint allows an unauthorized attacker to bypass a security feature over a network.

## Affected

- `sharepoint_enterprise_server_2016 >= 16.0.0 < 16.0.5561.1001`
- `sharepoint_server_2019 >= 16.0.0 < 16.0.10417.20175`
- `sharepoint_server_subscription_edition >= 16.0.0 < 16.0.19725.20434`

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.