CVE-2026-55009

Microsoft Exchange Server Elevation of Privilege Vulnerability

CVE-2026-55009 is fixed in 4 products on 1 platform, first by KB5103215, released June 9, 2026. It is not reported as exploited. Patch Radar priority: High.

High

CVSS

7.8

Important

Exploitation

None reported

Exploitation Unlikely

CISA KEV

Not listed

Not in the Known Exploited Vulnerabilities catalog

EPSS

0.0251

84th percentile

<p>Deserialization of untrusted data in Microsoft Exchange Server allows an authorized attacker to elevate privileges locally.</p>

Where it's fixed

Product	Fix	Released
Microsoft
Microsoft Exchange Server 2016 Cumulative Update 23	KB5103215	Jun 9, 2026
Microsoft Exchange Server 2019 Cumulative Update 14	KB5103214	Jun 9, 2026
Microsoft Exchange Server 2019 Cumulative Update 15	KB5103213	Jun 9, 2026
Microsoft Exchange Server Subscription Edition RTM	KB5103212	Jun 9, 2026

Details

Published
July 14, 2026
Weakness
Deserialization of Untrusted Data
Vendor advisory
https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-55009

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