CVE-2026-21511: 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
- More Likely
- Patch Tuesday
- 2026-Feb
- Released
- 2026-02-10
- Last Updated
- 2026-02-11
- EPSS Score
- 0.23% (percentile: 45.6%)
Description
Deserialization of untrusted data in Microsoft Office Outlook allows an unauthorized attacker to perform spoofing over a network.
FAQ
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.
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.
Affected Products (15)
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 for Mac 2021
- 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 Office LTSC for Mac 2024
- Microsoft Word 2016 (32-bit edition)
- Microsoft Word 2016 (64-bit edition)
Security Updates (7)
Acknowledgments
Office Product Group Security Team, Anonymous
Revision History
- 2026-02-10: Information published.
- 2026-02-11: Acknowledgement added. This is an informational change only.