CVE-2026-100404

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

MEDIUM
6.5
CVSS Score
Published: October 14, 2026 at 03:50 PM UTC
Updated: October 29, 2026 at 03:17 PM UTC
1 product affected across 1 vendorZulip

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Severity
MEDIUM6.5
Exploit prediction
EPSS 0.4%
SSVC
No known exploit

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.

Affected

Our own answer: ranges merged, affected separated from platform-only, with confidence and review flags.

v < 12.2

Remediation

No guide yet

No remediation guidance has been written for this CVE yet, and no fixed version or vendor advisory is recorded against it.

SSVC — Action Prioritization

SSVCNo known exploitNot automatablePartial impact

SSVC signals action urgency (what to patch first), separate from CVSS which measures severity.

CVSS

6.5MEDIUMGitHub_M
Attack Vector
NETWORK
Complexity
LOW
Privileges
LOW
User Interaction
NONE
Scope
UNCHANGED
Confidentiality
HIGH
Integrity
NONE
Availability
NONE
Vector?

Quick Info

StatusAWAITING ANALYSIS
CWE
CWE-862

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