{"id":"CVE-2026-93628","published":"2026-10-23T14:17:56.667","lastModified":"2026-10-23T16:44:17.950","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 An attacker who knows the meeting UID, organizer address and attendee address can send a non-outdated reply that changes the attendee's participation status in the organizer's calendar.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.","cvssScore":5.3,"cvssSeverity":"MEDIUM","cvssVector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N","cwes":["CWE-290"],"vendors":[],"products":[],"references":[{"url":"https://wiki.zimbra.com/wiki/Zimbra_Security_Advisories","tags":[]},{"url":"https://www.rapid7.com/blog/post/ve-breaking-zimbra-identity-boundaries-part-1/","tags":[]}],"exploitRefs":[],"hasPoc":false,"ai":null}