CVE-2026-56191

Improper authentication in Microsoft Exchange Online allows an unauthorized attacker to perform tampering over a network.

CVSS vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H

• https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-56191