CVE-2026-87696: Microsoft Exchange Server Elevation of Privilege Vulnerability

Severity: high (CVSS 7.5 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.4% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-10-13 · updated 2026-10-28
Weakness: CWE-347

Description

Improper verification of cryptographic signature in Microsoft Exchange Server allows an authorized attacker to elevate privileges 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 15.02.2562.056 — fixed in 15.02.2562.056
Microsoft Exchange Server 2016 Cumulative Update 23: from 15.01.0.0 before 15.01.2507.077 — fixed in 15.01.2507.077
Microsoft Exchange Server 2019 Cumulative Update 14: from 15.02.0.0 before 15.02.1544.050 — fixed in 15.02.1544.050
Microsoft Exchange Server 2019 Cumulative Update 15: from 15.02.0.0 before 15.02.1748.055 — fixed in 15.02.1748.055
Microsoft Exchange Server Subscription Edition RTM: from 15.02.0.0 before 15.02.2562.056 — fixed in 15.02.2562.056

How to fix

Upgrade to a fixed version: Microsoft Exchange Server Subscription Edition 15.02.2562.056; Microsoft Exchange Server 2016 Cumulative Update 23 15.01.2507.077; Microsoft Exchange Server 2019 Cumulative Update 14 15.02.1544.050; Microsoft Exchange Server 2019 Cumulative Update 15 15.02.1748.055; Microsoft Exchange Server Subscription Edition RTM 15.02.2562.056. Check the vendor advisory for mitigations.

References

https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-87696

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