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

MITRE NVD CVE.ORG JSON API

Summary

CVECVE-2026-100404
StatePUBLISHED
AssignerGitHub_M
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-10-14 16:17:28 UTC
Updated2026-10-14 16:17:28 UTC
DescriptionZulip 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.

Risk And Classification

Primary CVSS: v3.1 6.5 MEDIUM from [email protected]

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

Problem Types: CWE-862 | CWE-862 CWE-862: Missing Authorization

VersionSourceTypeScoreSeverityVector
3.1[email protected]Secondary6.5MEDIUMCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N
3.1CNADECLARED6.5MEDIUMCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N

CVSS v3.1 Breakdown

Attack Vector
Network
Attack Complexity
Low
Privileges Required
Low
User Interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
None
Availability
None

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

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Zulip Zulip affected < 12.2 Not specified

References

ReferenceSourceLinkTags
github.com/zulip/zulip/releases/tag/12.2 [email protected] github.com
github.com/zulip/zulip/pull/39913 [email protected] github.com
github.com/zulip/zulip/commit/98659a41cb93d4ce329ea14bb0cdfb4b147500ba [email protected] github.com
github.com/zulip/zulip/security/advisories/GHSA-5r8f-gq2h-fcgp [email protected] github.com
github.com/zulip/zulip/commit/c03db8916456674df3c98614f6f0ef8cd024ef11 [email protected] github.com
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