PT-2026-64208 · Microsoft · Exchange Online

CVE-2026-56191 · Published 2026-07-24 · Updated 2026-07-24

NVD

CVSS v3.1

10

Critical

Base vector

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

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

Fix

Improper Authentication

Weakness Enumeration

CWE-287

Related Identifiers

CVE-2026-56191

Affected Products

Exchange Online

References · 2

• https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-56191 · Vendor Advisory
• https://nvd.nist.gov/vuln/detail/CVE-2026-56191 · Security Note