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Vulnerability record · CVE-2026-21511 · published 10 February 2026

CVE-2026-21511: Microsoft 365 apps deserialization of untrusted data vulnerability

Microsoft · 365 Apps

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

7.5 CVSS 3.1 High EPSS 3.8% · top 10.5% CWE-502 · Deserialization of untrusted data
7.5CVSS 3.1 base score
3.8%EPSS exploitation probability, 30 days
NoNot in CISA KEV
5Affected product versions listed by NVD
1References
17 Jun 2026Last modified by NVD

Description

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

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N

Affected products

5 vulnerable configurations from NVD's CPE data, grouped by vendor and product.

References

LinkTags
https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-21511 Vendor Advisory

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Related vulnerabilities

Same products first, then exploited flaws of the same weakness class.

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Source: NIST National Vulnerability Database (record CVE-2026-21511), CISA KEV, FIRST EPSS (scores of 2026-09-26). This page is refreshed as NVD updates the record.