CVE-2026-100404

MEDIUM 6.5

Zulip: Guests can read new messages in non-subscribed public channels

CVSS Score

6.5

EPSS Score

0.0%

EPSS Percentile

0th

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.

CWE	CWE-862
Vendor	zulip
Product	zulip
Published	Oct 14, 2026

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CVSS v3 Breakdown

CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N

Attack Vector

Network

Attack Complexity

Low

Privileges Required

Low

User Interaction

None

Scope

Unchanged

Confidentiality

High

Integrity

None

Availability

None

Affected Versions

zulip / zulip

< 12.2

References

NVD ↗ CVE.org ↗ EPSS Data ↗

github.com: https://github.com/zulip/zulip/security/advisories/GHSA-5r8f-gq2h-fcgp github.com: https://github.com/zulip/zulip/pull/39913 github.com: https://github.com/zulip/zulip/commit/98659a41cb93d4ce329ea14bb0cdfb4b147500ba github.com: https://github.com/zulip/zulip/commit/c03db8916456674df3c98614f6f0ef8cd024ef11 github.com: https://github.com/zulip/zulip/releases/tag/12.2