Microsoft Security Response CenterCVE-2026-56191

Microsoft Exchange Online Tampering Vulnerability

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

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10.0CVSS out of 10Critical severity

Scope

What the vendor says is affected

Microsoft Exchange Online

Timeline

When this advisory changed

Jul 23, 2026 at 7:00 AM UTC
Published by Microsoft Security Response Center
The publication date reported by the vendor.
Sep 28, 2026 at 11:20 AM UTC
Added to SecurityAlert
We collected the advisory from the official source.

Vulnerabilities

CVEs named in this advisory

CVE-2026-56191View CVSS, KEV, EPSS, and threat context

Source

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Vendor: Microsoft Security Response Center
Advisory ID: CVE-2026-56191
Last source check: Sep 28, 2026 at 11:20 AM UTC

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What the vendor says is affected

When this advisory changed

CVEs named in this advisory

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