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CVE-2026-100404— Zulip: Guests can read new messages in non-subscribed public channels

Quick assessment

Affected
zulip zulip
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

Zulip 是一款开源的团队协作者工具。在 Zulip Server 12.1 及更早版本中，访客用户可能会接收到其未订阅的公开频道中的新消息事件。访客可以通过注册带有参数的事件队列，请求获取未订阅的公开频道的消息来触发此漏洞；或者，即使已移除访客对该频道的访问权限，其现有的事件队列仍可能持续受到影响。该漏洞会导致新发布的公开频道消息被泄露给访客用户。此问题已在版本 12.2 中修复。

CVSS 6.5 · Medium EPSS 0.41% · P34

Possible ATT&CK Techniques 1 AI

T1530 · Data from Cloud Storage

Affected Version Matrix 1

VendorProduct Version RangeStatus
zulip zulip < 12.2 affected
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I. Basic Information for CVE-2026-100404

Vulnerability Information
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Vulnerability Title
Zulip: Guests can read new messages in non-subscribed public channels
Source: CVE Program / CVE List V5
Vulnerability Description
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.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N
Source: CVE Program / CVE List V5
Vulnerability Type
授权机制缺失
Source: CVE Program / CVE List V5

Affected Products

Vendor Product Affected Versions CPE Subscribe
zulip zulip < 12.2 -

II. Public POCs for CVE-2026-100404

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III. Intelligence Information for CVE-2026-100404

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Patches & Fixes for CVE-2026-100404 (3)

Other References for CVE-2026-100404 (2)

IV. Related Vulnerabilities

Same product: zulip
Same vendor: zulip
Same weakness: CWE-862

V. Comments for CVE-2026-100404

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