{"id":"CVE-2026-56191","title":"Microsoft Exchange Online Tampering Vulnerability","summary":"Improper authentication in Microsoft Exchange Online allows an unauthorized attacker to perform tampering over a network.","severity":"critical","cvss":10,"cvssVector":"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","cvssSource":"cna","cwe":["CWE-287"],"vendor":"Microsoft","product":"Microsoft Exchange Online","affected":["exchange_online -"],"ssvc":{"exploitation":"none","automatable":"yes","technicalImpact":"total","timestamp":"2026-07-24T00:00:00+00:00"},"published":"2026-07-24","updated":"2026-09-17","sourceUpdated":"2026-09-17T22:34:32.093Z","source":"CVEORG","sourceUrl":"https://www.cve.org/CVERecord?id=CVE-2026-56191","references":[{"url":"https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-56191","label":"Microsoft Exchange Online Tampering Vulnerability"}],"tags":["cve.org"],"epss":0.00756,"epssPercentile":0.5366,"ingestedAt":"2026-09-08T17:06:31.892Z","slug":"CVE-2026-56191","body":"## Overview\n\nImproper authentication in Microsoft Exchange Online allows an unauthorized attacker to perform tampering over a network.\n\n## Affected\n\n- `exchange_online -`\n\n## Remediation\n\nRefer to the linked advisories for vendor-supplied fixes and affected version ranges.","depth":"midnight","depthScore":55,"depthScoreParts":{"impact":55,"likelihood":0.2,"exploitation":0,"ransomware":0},"changes":[]}