{"id":"CVE-2026-56191","published":"2026-07-24T00:01:12Z","modified":"2026-10-28T20:07:13Z","title":"Microsoft Exchange Online Tampering Vulnerability","vendor":"Microsoft","product":"Microsoft Exchange Online","tier":"tail","description":{"text":"Improper authentication in Microsoft Exchange Online allows an unauthorized attacker to perform tampering over a network.","provenance":"source","from":"CVE.org"},"cvss":{"score":10,"severity":"CRITICAL","version":"3.1","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","provenance":"source","from":"CVE.org CNA"},"epss":{"score":0.00901,"percentile":0.59574,"provenance":"source"},"cwes":[{"id":"CWE-287","name":"Improper Authentication"}],"references":[{"url":"https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-56191","tags":["vendor-advisory","patch"]}],"priority":{"score":18.9,"factors":[{"name":"EPSS percentile","points":11.91},{"name":"CVSS severity","points":7.0}]},"vendorSlug":"microsoft","affectedVersions":[{"vendor":"Microsoft","product":"Microsoft Exchange Online","versions":["-"]}],"euvd":{"id":"EUVD-2026-48458","exploited":false,"provenance":"source"},"lineage":{"familyId":"fam-class-microsoft-exchange-server-cwe-287"}}