by Kastro
Paper/Archive/CVE-2026-56191

CVE-2026-56191

Microsoft Microsoft Exchange Online — Microsoft Exchange Online Tampering Vulnerability

EPSS 0.9%CVSS 10.0
critical.is priorityof 100
42
CVSS 10.0 (CNA)10.0 / 10 × 3030.0Not in CISA KEV+300.0EPSS percentile 59.6.596 × 2011.9No public exploit+100.0SSVC exploitation: none+100.0
Description · from the CVE record

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

Affected

ProductAffectedFixed inSource
Microsoft Exchange Online-–CNA

Scores by source

microsoft (CNA)10.0CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H/E:U/RL:O/RC:C
CISA ADPSSVCExploitation: none · Automatable: yes · Technical impact: total

References

patchmsrc.microsoft.com/update-guide/vulnerability/CVE-2026-56191