CVE-2026-93629: Zimbra Collaboration Suite Calendar Processing Authentication Bypass via Forged iCalendar REQUEST Organizer Identity
An organizer authentication vulnerability in Zimbra Collaboration Suite (ZCS) allows an unauthenticated email sender to insert calendar invitations attributed to another user. The email delivery path permits external invitations but does not verify that the message sender is authorized to use the iCalendar ORGANIZER identity. When automatic invitation insertion is enabled, a crafted REQUEST component creates an event containing attacker-selected meeting details and reminders under a forged organizer without recipient interaction. No corresponding event is created in the claimed organizer's calendar. ZCS 10.1.16 and 10.1.21 are affected.
Affected Software
Event History
Frequently Asked Questions
Which deployments are exposed to this issue?
Zimbra Collaboration Suite 10.1.16 and 10.1.21 are affected. Exposure requires automatic invitation insertion to be enabled for recipients.
What does an attacker need to exploit it?
An attacker only needs to send a crafted external calendar invitation email containing an iCalendar REQUEST component with a forged ORGANIZER identity. No authentication or recipient interaction is required when automatic invitation insertion is enabled.
What is the practical impact on a recipient?
A crafted invitation can be inserted into the recipient's calendar with attacker-selected meeting details and reminders while appearing to come from another user. The claimed organizer does not receive a corresponding calendar event.
What can be done if updates cannot be applied immediately?
Disable automatic invitation insertion for recipients to prevent crafted external REQUEST invitations from being added without interaction.