CVE-2026-56191

Severity CVSS v4.0:

Pending analysis

Type:

CWE-287 Authentication Issues

Publication date:

24/07/2026

Last modified:

29/07/2026

Description

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

Impact

Vector 3.x

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H CVSS v3.1 Severity and Metrics:

Base Score: 10.00 CRITICAL
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H

Attack Vector (AV): Network
Attack Complexity (AC): Low
Privileges Required (PR): None
User Interaction (UI): None
Scope (S): Changed
Confidentiality (C): High
Integrity (I): High
Availability (A): High

Base Score 3.x

10.00

Severity 3.x

CRITICAL

Vulnerable products and versions

CPE	From	Up to
cpe:2.3:a:microsoft:exchange_online:-:::::::*

To consult the complete list of CPE names with products and versions, see this page

References to Advisories, Solutions, and Tools

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