Live › vulnerability › CVE-2026-93628
Go to dashboardZimbra Collaboration Suite skips its attendee authorization check when processing iCalendar REPLY messages, so an unauthenticated sender can forge another attendee's response to a meeting. An attacker who knows the meeting UID, organizer and attendee addresses can change that attendee's participation status in the organizer's calendar.
Summary written from the sources below. Check the originals before acting.
First seen by InfraStack 2026-10-23 21:57 UTC. All times on this page are UTC.
Organizations running Zimbra Collaboration Suite 10.1.16 or 10.1.21 that receive calendar invitations by email are exposed, because the flaw is in automatic delivery of inbound iCalendar replies. Teams on other Zimbra versions, or on hosted Zimbra with the vendor patching for them, can skip it, though the sources do not confirm which versions are unaffected.
No product ranges from the sources yet.
su - zimbra -c "zmcontrol -v"; the sources name ZCS 10.1.16 and 10.1.21 as affected10.1.16 and 10.1.21 builds to a fixed release; the fixed version is unknown from the sourcesEach row is the first time that source carried this signal. The analyst’s rows are its own findings.
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 An attacker who knows the meeting UID, organizer address and attendee address can send a non-outdated reply that changes the attendee's participation status in the organizer's calendar.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.
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