---
id: CVE-2026-93627
title: >-
  Zimbra Collaboration Suite Calendar Processing Authentication Bypass via
  Forged iCalendar CANCEL/REQUEST Organizer
summary: >-
  An organizer authentication vulnerability in the email calendar processing of
  Zimbra Collaboration Suite (ZCS) allows an unauthenticated sender to cancel or
  modify an existing meeting in a recipient's calendar. Zimbra accepts iCalendar
  C…
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: '2026-10-23T13:17:00.739Z'
source: CVEORG
sourceUrl: 'https://www.cve.org/CVERecord?id=CVE-2026-93627'
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: '2026-10-23T14:28:08.715Z'
---

## Overview

An organizer authentication vulnerability in the email calendar processing of Zimbra Collaboration Suite (ZCS) allows an unauthenticated sender to cancel or modify an existing meeting in a recipient's calendar. Zimbra accepts iCalendar CANCEL and REQUEST components without verifying that the email sender is authorized to act as the supplied organizer. An attacker who knows the meeting UID and organizer address can supply a non-outdated sequence number to move the recipient's meeting to Trash or replace its details. Processing occurs automatically during email delivery without recipient interaction. ZCS 10.1.16 and 10.1.21 are affected.

## Affected

- `collaboration_suite <= 10.1.21`

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.