---
id: "CVE-2026-93629"
kind: "vulnerability"
aliases: ["CVE-2026-93629"]
title: "Zimbra: unauthenticated email can forge calendar invitations as another user"
severity: "medium"
cvss: 5.3
epss: 0.00376
exploited: false
status: "open"
category: "package"
products: []
ecosystems: []
tags: ["calendar", "email", "package", "self-hosted", "zimbra"]
not_affected_if: ["automatic-invitation-insertion-off"]
published_at: "2026-10-23T14:17:56+00:00"
first_seen_at: "2026-10-23T21:57:34+00:00"
updated_at: "2026-10-25T12:38:49+00:00"
sources: [{"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-93629", "first_seen_at": "2026-10-23T21:57:34+00:00"}, {"source": "epss", "url": "https://api.first.org/data/v1/epss?cve=CVE-2026-93629", "first_seen_at": "2026-10-25T12:38:49+00:00"}]
---

# Zimbra: unauthenticated email can forge calendar invitations as another user

Zimbra Collaboration Suite does not check that an emailed calendar invitation's ORGANIZER is allowed to send it, so an outside sender can create events attributed to another user. The attacker controls the meeting details and reminders, and the recipient does not need to interact.

_Summary, check and fix written by a model from the sources; labelled as such._

## How to check

- Check the installed Zimbra version with `su - zimbra -c "zmcontrol -v"`
- Check whether automatic invitation insertion is enabled for accounts that receive external mail (the sources do not name the exact setting, unknown)

## Fix

- Upgrade Zimbra Collaboration Suite to a release newer than `10.1.16` and `10.1.21` (the sources do not name the fixed version, unknown)
- Until patched, unknown mitigation

## Timeline

- 2026-10-23T21:57:34+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-93629
- 2026-10-25T12:38:49+00:00 epss https://api.first.org/data/v1/epss?cve=CVE-2026-93629

## From the sources

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.

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_Free to read at a human pace. An API with keys and an MCP server are in preparation; early access: hello@infrastack.ai_