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CVE-2026-56191

Microsoft Exchange Online authentication bypass

10.0 CRITICALEPSS 0.90%
  1. Published23 Jul 2026

Description

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

CVSS 3.1 breakdown

Attack vectorNetwork
Attack complexityLow
Privileges requiredNone
User interactionNone
ScopeChanged
ConfidentialityHigh
IntegrityHigh
AvailabilityHigh
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H

Affected products

Microsoft Exchange Onlineall versions

Remediation

No fixed version is recorded in the NVD data. Check the vendor advisory for the latest guidance.

References

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Frequently asked

Is CVE-2026-56191 being actively exploited?

CVE-2026-56191 is not in the CISA KEV catalog. Its EPSS exploit probability is 0.90%.

How severe is CVE-2026-56191?

CVE-2026-56191 has a CVSS 3.1 base score of 10.0, rated critical. EPSS estimates a 0.90% probability of exploitation.

Which products are affected by CVE-2026-56191?

Affected products include Microsoft Exchange Online.

How do I fix CVE-2026-56191?

Apply the vendor's patch or advisory guidance, then verify no affected versions remain across your devices.

How Secuno handles this

Secuno correlates vulnerabilities like CVE-2026-56191 against the real software inventory on every managed device, as each hourly inventory arrives. Rather than a static severity, each match is scored in context: exploit availability, EPSS, the asset's exposure, and business criticality decide where it lands in the queue. If an affected version is present anywhere across your portfolio, it surfaces automatically with a prioritised remediation path.

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Data from the NVD, CISA KEV catalog and FIRST EPSS. CVSS 3.1 base score shown where available.