CVE-2026-55040: Microsoft SharePoint Server Security Feature Bypass Vulnerability

Overview

Severity
Critical (CVSS 9.1)
CVSS Vector
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
Category
Security Feature Bypass
Exploit Status
Not Exploited
Exploitation Likelihood
More Likely
Patch Tuesday
2026-Jul
Released
2026-07-14

Description

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

FAQ

What kind of security feature could be bypassed by successfully exploiting this vulnerability? The authentication feature could be bypassed as this vulnerability allows impersonation. I am running SharePoint Server 2016. Do the updates for SharePoint Enterprise Server 2016 also apply to the version I am running? Yes. The same KB number applies to both SharePoint Server 2016 and SharePoint Enterprise Server 2016. Customers running either version should install the security update to be protected from this vulnerability. According to the CVSS metrics, successful exploitation of this vulnerability could lead to major loss of confidentiality (C:H), and integrity (I:H), but could lead to no loss of availability (A:N). What does that mean for this vulnerability? Exploiting this vulnerability could allow an attacker to disclose files and modify data, but the attacker cannot impact the availability of the system. How could an attacker exploit this vulnerability? In a network-based attack, an unauthenticated attacker could bypass authentication and make an anonymous connection.

Affected Products (3)

Microsoft Office

  • Microsoft SharePoint Enterprise Server 2016
  • Microsoft SharePoint Server 2019
  • Microsoft SharePoint Server Subscription Edition

Security Updates (3)

Acknowledgments

<a href="https://x.com/rm_rf_chumy">Chumy Tsai</a> with <a href="https://www.cycraft.com/">CyCraft Technology</a> , <a href="https://twitter.com/_l0gg">khoadha</a>, <a href="https://x.com/stephenfewer">Stephen Fewer</a> with <a href="https://www.rapid7.com/">Rapid7</a>

Revision History

  • 2026-07-14: Information published.