CVE-2026-20959: Microsoft SharePoint Server Spoofing Vulnerability

Overview

Severity
Medium (CVSS 4.6)
CVSS Vector
CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:U/C:L/I:L/A:N/E:U/RL:O/RC:C
Category
Spoofing
Exploit Status
Not Exploited
Exploitation Likelihood
Less Likely
Patch Tuesday
2026-Jan
Released
2026-01-13
EPSS Score
0.06% (percentile: 19.0%)

Description

Improper neutralization of input during web page generation ('cross-site scripting') in Microsoft Office SharePoint allows an authorized attacker to perform spoofing over a network.

FAQ

According to the CVSS metric, user interaction is required (UI:R) and privileges required is low (PR:L). What does that mean for this vulnerability? An authorized attacker must send the user a malicious link and convince the user to open it. According to the CVSS metrics, successful exploitation of this vulnerability could lead to some loss of confidentiality (C:L), and integrity (I:L) but lead to no loss of availability (A:N). What is the impact of this vulnerability? An attacker who successfully exploited the vulnerability could view some sensitive information (Confidentiality), make changes to disclosed information (Integrity), but cannot limit access to the resource (Availability).

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://ch.linkedin.com/in/martin-wrona-7746122b8">Martin Wrona (martin_jw)</a> with <a href="https://www.galaxus.ch/">Digitec Galaxus AG</a>

Revision History

  • 2026-01-13: Information published.