CVE-2026-21260: Microsoft Outlook Spoofing Vulnerability

Overview

Severity
High (CVSS 7.5)
CVSS Vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N/E:U/RL:O/RC:C
Category
Spoofing
Exploit Status
Not Exploited
Exploitation Likelihood
Unlikely
Patch Tuesday
2026-Feb
Released
2026-02-10
EPSS Score
0.05% (percentile: 15.0%)

Description

Exposure of sensitive information to an unauthorized actor in Microsoft Office Outlook allows an unauthorized attacker to perform spoofing over a network.

FAQ

There are multiple update packages available for some of the affected software. Do I need to install all the updates listed in the Security Updates table for the software? Yes. Customers should apply all updates offered for the software installed on their systems. If multiple updates apply, they can be installed in any order. Is the Preview Pane an attack vector for this vulnerability? Yes, the Preview Pane is an attack vector. How could an attacker exploit this vulnerability? An attacker could exploit this spoofing vulnerability by using a specially crafted email to trigger an outbound NTLM authentication attempt to an attacker‑controlled server, resulting in credential disclosure. Why isn’t there a security update for Outlook if Outlook is impacted? Microsoft Outlook may be involved in certain attack scenarios; however, the security update applies to Microsoft Word, which addresses the vulnerability. Installing the latest security update for Microsoft Word fully mitigates the vulnerability, including scenarios in which Outlook is used. There is no separate update required for Microsoft Outlook.

Affected Products (13)

Microsoft Office

  • Microsoft SharePoint Enterprise Server 2016
  • Microsoft SharePoint Server 2019
  • Microsoft Office 2019 for 32-bit editions
  • Microsoft Office 2019 for 64-bit editions
  • Microsoft 365 Apps for Enterprise for 32-bit Systems
  • Microsoft 365 Apps for Enterprise for 64-bit Systems
  • Microsoft Office LTSC 2021 for 64-bit editions
  • Microsoft Office LTSC 2021 for 32-bit editions
  • Microsoft SharePoint Server Subscription Edition
  • Microsoft Office LTSC 2024 for 32-bit editions
  • Microsoft Office LTSC 2024 for 64-bit editions
  • Microsoft Outlook 2016 (32-bit edition)
  • Microsoft Outlook 2016 (64-bit edition)

Security Updates (6)

Acknowledgments

<a href="https://erpaciocco.github.io/">ErPaciocco</a>

Revision History

  • 2026-02-10: Information published.