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No exploitation reportedFix available

CVE-2026-21511

Microsoft Outlook Spoofing Vulnerability

No exploitation reported by the sources we read.

  • Published2026-02-10
  • Fixed in16.0.19127.20518
  • WeaknessCWE-502

Am I affected?

With a domain, we read the version its public headers and pages expose. A distribution build can carry the fix under an older number.

Description

Deserialization of untrusted data in Microsoft Office Outlook allows an unauthorized attacker to perform spoofing over a network.

Timeline

dates in UTC
  1. 2026-02-1018:16CVE publishedNVD

Versions per branch

NVD
Microsoft sharepoint server
BranchAffectedFixed in
16.0< 16.0.19127.2051816.0.19127.20518
2016.x= 2016no fix published
2019.x= 2019no fix published
Microsoft office long term servicing channel
BranchAffectedFixed in
2021.x= 2021no fix published
2024.x= 2024no fix published
Microsoft 365 apps
BranchAffectedFixed in
—all versionsno fix published

2 more products in the sources.

as publishedRanges as NVD and OSV publish them; a distribution’s build can be fixed under an older number.

Products declared by the CNA10 products

As microsoft, the CNA that assigned this CVE, declared them in the CVE record; versions as written.

  • Microsoft 365 Apps for Enterprise

    platforms: 32-bit Systems, x64-based Systems

    Affected
    • ≥ 16.0.1, < https://aka.ms/OfficeSecurityReleasesfixed in https://aka.ms/OfficeSecurityReleasescustom
  • Microsoft Office 2019

    platforms: 32-bit Systems, x64-based Systems

    Affected
    • ≥ 19.0.0, < https://aka.ms/OfficeSecurityReleasesfixed in https://aka.ms/OfficeSecurityReleasescustom
  • Microsoft Office LTSC 2021

    platforms: 32-bit Systems, x64-based Systems

    Affected
    • ≥ 16.0.1, < https://aka.ms/OfficeSecurityReleasesfixed in https://aka.ms/OfficeSecurityReleasescustom
  • Microsoft Office LTSC 2024

    platforms: 32-bit Systems, x64-based Systems

    Affected
    • ≥ 16.0.0, < https://aka.ms/OfficeSecurityReleasesfixed in https://aka.ms/OfficeSecurityReleasescustom
  • Microsoft Office LTSC for Mac 2021
    Affected
    • ≥ 16.0.1, < 16.106.26020821fixed in 16.106.26020821custom
  • Microsoft Office LTSC for Mac 2024
    Affected
    • ≥ 16.0.0, < 16.106.26020821fixed in 16.106.26020821custom

4 more products in the CVE record.

Source: the CNA record (CVE Program), © The MITRE Corporation,CVE Terms of UseCVE recordupdated 2026-08-19

Fix

  1. Update Microsoft sharepoint server to 16.0.19127.20518

Advisories and patches

Detection

Nuclei template
none so far
ProjectDiscovery
Exploit-DB
no entry
Exploit-DB
Proof of concept
Metasploit modules
none listed
Metasploit Framework

Sources

Identifiers

Technical details

CVSS v3 Vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N
Published
2026-02-10
Last Modified
2026-06-17
NVD status
Analyzed
GitHub Advisory
GHSA-x27j-2rq3-h4mw

Frequently asked questions

What is CVE-2026-21511?

Deserialization of untrusted data in Microsoft Office Outlook allows an unauthorized attacker to perform spoofing over a network.

Is CVE-2026-21511 actively exploited?

Active exploitation of CVE-2026-21511 has not been confirmed. Its EPSS score was 4.0% on 2026-11-09, the estimated probability of exploitation in the next 30 days.

What is the CVSS score for CVE-2026-21511?

CVE-2026-21511 has a CVSS v3 base score of 7.5 (HIGH severity), with vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N.

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