CVE-2026-55008

Microsoft Exchange Server Spoofing Vulnerability

CVE-2026-55008 is fixed in 4 products on 1 platform, first by KB5103215, released June 9, 2026. It is not reported as exploited, but the vendor rates exploitation more likely. Patch Radar priority: Urgent.

Urgent

CVSS

9.6

Critical

Exploitation

More likely

Vendor assessment

CISA KEV

Not listed

Not in the Known Exploited Vulnerabilities catalog

EPSS

0.0086

58th percentile

<p>Improper neutralization of input during web page generation ('cross-site scripting') in Microsoft Exchange Server allows an unauthorized attacker to perform spoofing over a network.</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
Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
Vendor advisory
https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-55008

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