CVE-2025-64666: Microsoft Exchange Server Elevation of Privilege Vulnerability

Severity: high (CVSS 7.5 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 1.0% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2025-12-09 · updated 2026-10-14
Weakness: CWE-20

Description

Improper input validation in Microsoft Exchange Server allows an authorized attacker to elevate privileges over a network.

Affected products

Microsoft Exchange Server: 2016-cumulative_update_1, 2016-cumulative_update_10, 2016-cumulative_update_11, 2016-cumulative_update_12, 2016-cumulative_update_13, 2016-cumulative_update_14 (+29); 2016, 2019
Microsoft Exchange Server Subscription Edition: before 15.02.2562.035 — fixed in 15.02.2562.035
Microsoft Exchange Server 2016 Cumulative Update 23: from 15.01.0.0 before 15.01.2507.063 — fixed in 15.01.2507.063
Microsoft Exchange Server 2019 Cumulative Update 14: from 15.02.0.0 before 15.02.1544.037 — fixed in 15.02.1544.037
Microsoft Exchange Server 2019 Cumulative Update 15: from 15.02.0.0 before 15.02.1748.042 — fixed in 15.02.1748.042
Microsoft Exchange Server Subscription Edition RTM: from 15.02.0.0 before 15.02.2562.035 — fixed in 15.02.2562.035

How to fix

Upgrade to a fixed version: Microsoft Exchange Server Subscription Edition 15.02.2562.035; Microsoft Exchange Server 2016 Cumulative Update 23 15.01.2507.063; Microsoft Exchange Server 2019 Cumulative Update 14 15.02.1544.037; Microsoft Exchange Server 2019 Cumulative Update 15 15.02.1748.042; Microsoft Exchange Server Subscription Edition RTM 15.02.2562.035. Check the vendor advisory for mitigations.

References

https://msrc.microsoft.com/update-guide/vulnerability/CVE-2025-64666

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