{"id":"CVE-2026-93628","aliases":[],"title":"Zimbra Collaboration Suite Calendar Processing Authentication Bypass via Forged iCalendar REPLY Attendee Response","titleSource":"rapid7","descriptionSource":"rapid7","products":[{"vendor":"Zimbra","name":"Zimbra Collaboration Suite","platforms":[],"versions":[{"version":"0","status":"affected","lessThanOrEqual":"10.1.21","versionType":"semver"}],"defaultStatus":"unaffected","source":"rapid7","url":"https://www.cve.org/CVERecord?id=CVE-2026-93628"}],"remediation":[],"description":"An attendee authentication vulnerability in the email calendar processing of Zimbra Collaboration Suite (ZCS) allows an unauthenticated sender to forge another attendee's response to an existing meeting. Zimbra passes a null sender identity when processing iCalendar REPLY components, causing the attendee authorization filter to be skipped. An attacker who knows the meeting UID, organizer address and attendee address can send a non-outdated reply that changes the attendee's participation status in the organizer's calendar. The change occurs automatically during delivery without organizer or attendee interaction. ZCS 10.1.16 and 10.1.21 are affected.","severity":"medium","score":5.3,"published":"2026-10-23T13:18:16.368Z","modified":"2026-10-28T20:02:01.885Z","withdrawn":false,"knownExploited":false,"affected":[],"references":["https://wiki.zimbra.com/wiki/Zimbra_Security_Advisories","https://www.rapid7.com/blog/post/ve-breaking-zimbra-identity-boundaries-part-1/"],"sources":[{"name":"CVE","id":"CVE-2026-93628","modified":"2026-10-28T20:02:01.885Z","url":"https://www.cve.org/CVERecord?id=CVE-2026-93628"}],"assessments":[{"source":"rapid7","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N","score":5.3}],"sourceAffected":[],"kev":{"status":"not-listed","checkedAt":"2026-10-29T03:15:31.428Z"},"coverage":[{"source":"NVD","status":"not-checked"},{"source":"GHSA","status":"not-checked"},{"source":"EUVD","status":"not-checked"},{"source":"EPSS","status":"not-checked"}],"evidence":[]}