CVE-2026-56191: Microsoft Exchange Online

Critical severity, CVSS 10.0. EPSS: 0.9% chance of exploitation in the next 30 days.

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

Affected products

• Microsoft Exchange Online: affected versions not specified

Published 2026-07-24. Last modified 2026-07-29.