CVE-2026-56191

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

CVSS 3.1

10.0CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H

EPSS

0.9% chance of exploitation in the next 30 days; higher than 59% of CVEs (scores of 2026-10-25)

CWE

CWE-287

Published

2026-07-24

Modified

2026-10-24

Record from

the NVD, synced 2026-10-24

Affected

• microsoft:exchange_online

References

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

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