CVE-2026-87696 Microsoft Exchange Server - Authentication Bypass

Microsoft Exchange Server contains a broken authentication vulnerability caused by improper verification of cryptographic signatures, letting authorized attackers elevate privileges over a network, exploit requires attacker to be authorized.

CVSS base score 7.5 /10
High
CISA KEV
Not listed
Public exploit
None known
Authentication
Required
EPSS
0.38% chance of exploitation in 30 days
View the NVD record ↗

Details

Type
Authentication Bypass
Impact
Privilege Escalation
CVSS vector
CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H
Published
13 October 2026
Updated
15 October 2026
Weakness
CWE-347

Vendor fix

Update to the latest available version of Microsoft Exchange Server.

Patching closes this CVE. It does not tell you which of your systems run the affected version, or what else is exposed alongside them.

References

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