CVE-2026-21527: Microsoft Exchange Server Spoofing Vulnerability

Severity: medium (CVSS 6.5 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 8.3% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-02-10 · updated 2026-08-19
Weakness: CWE-345

Description

User interface (ui) misrepresentation of critical information in Microsoft Exchange Server allows an unauthorized attacker to perform spoofing over a network.

Affected products

Microsoft Exchange Server: 2016-cumulative_update_23, 2019-cumulative_update_14, 2019-cumulative_update_15
Microsoft Exchange Server Subscription Edition: before 15.02.2562.037 — fixed in 15.02.2562.037
Microsoft Exchange Server 2016 Cumulative Update 23: from 15.01.0.0 before 15.01.2507.066 — fixed in 15.01.2507.066
Microsoft Exchange Server 2019 Cumulative Update 14: from 15.02.0.0 before 15.02.1544.039 — fixed in 15.02.1544.039
Microsoft Exchange Server 2019 Cumulative Update 15: from 15.02.0.0 before 15.02.1748.043 — fixed in 15.02.1748.043
Microsoft Exchange Server Subscription Edition RTM: from 15.02.0.0 before 15.02.2562.037 — fixed in 15.02.2562.037

How to fix

Upgrade to a fixed version: Microsoft Exchange Server Subscription Edition 15.02.2562.037; Microsoft Exchange Server 2016 Cumulative Update 23 15.01.2507.066; Microsoft Exchange Server 2019 Cumulative Update 14 15.02.1544.039; Microsoft Exchange Server 2019 Cumulative Update 15 15.02.1748.043; Microsoft Exchange Server Subscription Edition RTM 15.02.2562.037. Check the vendor advisory for mitigations.

References

https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-21527

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