{"id":"CVE-2026-93628","title":"Zimbra Collaboration Suite Calendar Processing Authentication Bypass via Forged iCalendar REPLY Attendee Response","summary":"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 ident…","severity":"medium","cvss":5.3,"cvssVector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N","cvssSource":"cna","cwe":["CWE-290"],"vendor":"Zimbra","product":"Zimbra Collaboration Suite","affected":["collaboration_suite <= 10.1.21"],"published":"2026-10-23","updated":"2026-10-23","sourceUpdated":"2026-10-23T13:18:16.368Z","source":"CVEORG","sourceUrl":"https://www.cve.org/CVERecord?id=CVE-2026-93628","references":[{"url":"https://wiki.zimbra.com/wiki/Zimbra_Security_Advisories"},{"url":"https://www.rapid7.com/blog/post/ve-breaking-zimbra-identity-boundaries-part-1/"}],"tags":["cve.org"],"ingestedAt":"2026-10-23T14:28:08.713Z","slug":"CVE-2026-93628","body":"## Overview\n\nAn 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 An attacker who knows the meeting UID, organizer address and attendee address can send a non-outdated reply that changes the attendee's participation status in the organizer's calendar.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.\n\n## Affected\n\n- `collaboration_suite <= 10.1.21`\n\n## Remediation\n\nRefer to the linked advisories for vendor-supplied fixes and affected version ranges.","depth":"sunlit","depthScore":29,"depthScoreParts":{"impact":29.2,"likelihood":0,"exploitation":0,"ransomware":0},"changes":[]}