---
id: CVE-2026-100404
title: Zulip is an open-source team collaboration tool
summary: >-
  Zulip is an open-source team collaboration tool. In Zulip Server versions
  through 12.1, guest users can receive new message events for public channels
  outside their subscriptions. A guest can trigger the issue by registering an
  event que…
severity: medium
cvss: 6.5
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N'
cwe:
  - CWE-862
published: '2026-10-14'
updated: '2026-10-14'
sourceUpdated: '2026-10-14T16:17:28.860'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-100404'
references:
  - url: >-
      https://github.com/zulip/zulip/commit/98659a41cb93d4ce329ea14bb0cdfb4b147500ba
    label: security-advisories@github.com
  - url: >-
      https://github.com/zulip/zulip/commit/c03db8916456674df3c98614f6f0ef8cd024ef11
    label: security-advisories@github.com
  - url: 'https://github.com/zulip/zulip/pull/39913'
    label: security-advisories@github.com
  - url: 'https://github.com/zulip/zulip/releases/tag/12.2'
    label: security-advisories@github.com
  - url: 'https://github.com/zulip/zulip/security/advisories/GHSA-5r8f-gq2h-fcgp'
    label: security-advisories@github.com
tags:
  - nvd
ingestedAt: '2026-10-14T16:40:32.110Z'
---

## Overview

Zulip is an open-source team collaboration tool. In Zulip Server versions through 12.1, guest users can receive new message events for public channels outside their subscriptions. A guest can trigger the issue by registering an event queue with parameters that request messages from an unsubscribed public channel, or an existing event queue can remain affected after the guest's access to the channel is removed. The flaw discloses new public-channel messages to the guest. This issue is fixed in version 12.2.

## Remediation

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