CVE-2026-56191CWE-287

Microsoft Exchange Online Tampering Vulnerability

Critical · published July 24, 2026

CVSS v3.1
10.0
EPSS
1%
Percentile
59.3
In the wild
Unconfirmed
What it is

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

The record
Technical detail
CVSS v3.1
10.0 · CRITICAL
Vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H/E:U/RL:O/RC:C
CVSS v4.0
Not supplied
EPSS
0.00901 · 59.3th percentile
Weakness
CWE-287 · Improper Authentication
Published
2026-07-24T00:01Z
EPSS history
Timeline
  • 24 JUL 00:01Z
    Microsoft Exchange Online Tampering Vulnerability
    cvelistv5