High severity · published Feb 10, 2026
CVE-2026-21511
Microsoft Outlook Spoofing Vulnerability
7.5
CVSS
4%
EPSS
No
On KEV
Description
Deserialization of untrusted data in Microsoft Office Outlook allows an unauthorized attacker to perform spoofing over a network.
CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
None
Confidentiality
High
Integrity
None
Availability
None
Scope
Unchanged
Exploitation
Is it being used?
Exploit prediction (EPSS)4.0% · higher than 90% of CVEs
Exploited in the wildNo evidence yet
CISA KEVNot listed
Ransomware campaign useNot known
Affected products
Which versions
OF
Office · Microsoft
2019; 2019 · source: NVD
SH
SharePoint · Microsoft
before 16.0.19127.20518; 2016; 2019 · source: NVD
M3
Microsoft 365 Apps for Enterprise · Microsoft
16.0.1 before https://aka.ms/OfficeSecurityReleases · source: vendor
MO
Microsoft Office 2019 · Microsoft
19.0.0 before https://aka.ms/OfficeSecurityReleases · source: vendor
MO
Microsoft Office LTSC 2021 · Microsoft
16.0.1 before https://aka.ms/OfficeSecurityReleases · source: vendor
MO
Microsoft Office LTSC 2024 · Microsoft
16.0.0 before https://aka.ms/OfficeSecurityReleases · source: vendor
MO
Microsoft Office LTSC for Mac 2021 · Microsoft
16.0.1 before 16.106.26020821 · source: vendor
MO
Microsoft Office LTSC for Mac 2024 · Microsoft
16.0.0 before 16.106.26020821 · source: vendor
MS
Microsoft SharePoint Enterprise Server 2016 · Microsoft
16.0.0 before 16.0.5539.1002 · source: vendor
MS
Microsoft SharePoint Server 2019 · Microsoft
16.0.0 before 16.0.10417.20097 · source: vendor
MS
Microsoft SharePoint Server Subscription Edition · Microsoft
16.0.0 before 16.0.19127.20518 · source: vendor
MW
Microsoft Word 2016 · Microsoft
16.0.1 before 16.0.5539.1002 · source: vendor
References
NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-21511
CVE.org
https://www.cve.org/CVERecord?id=CVE-2026-21511
Vendor Advisory
https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-21511
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