Medium · CVSS 6.5CVE-2026-100404

Zulip: Guests can read new messages in non-subscribed public channelsCVE-2026-100404

Answer in brief

CVE-2026-100404 records a Medium severity (CVSS 6.5) vulnerability in Zulip: Guests can read new messages in non-subscribed public channels. The current sources do not mark it as known exploited. The current feed maps zulip/zulip (generic). Check affected ranges and fixed versions before updating.

Analysis pending evidence review

HOL Guard separates source facts from reviewed analysis. See the methodology.

Published Oct 14, 2026Updated Oct 14, 2026Source checked Oct 14, 2026First seen by HOL Oct 14, 2026Material review Oct 14, 2026

Upstream Advisory

Key facts

Risk: Medium · CVSS 6.5
Exploitation: Not marked as known exploited
Affected software: 1 mapped package or product
Fix availability: Available

Why this deserves its current priority

CVSS is 6.5. The current sources do not mark it as known exploited. Treat this as a source-backed prioritization signal, not a statement about your environment.

Analysis status

Analysis pending evidence review

Factual feed record only; HOL analysis is not approved for indexing. Read the methodology.

Affected scope and exposure questions

The current feed maps zulip/zulip (generic). Check affected ranges and fixed versions before updating.

Mapped affected packages and fixed versions
Package	Affected range	Fixed version
zulip/zulipgeneric	<12.2	12.2

Recommended response

Check inventory. Check lockfiles and deployed manifests for zulip/zulip.
Review the reported fix. Update zulip/zulip to 12.2 if you use the affected versions. Test the change in a non-production environment first.

Evidence timeline and material changes

Published upstream
Oct 14, 2026
Evidence: source:cvelist:source_dates:source-dates:record
Source modified
Oct 14, 2026
Evidence: source:cvelist:source_dates:source-dates:record
First seen by HOL
Oct 14, 2026

Sources and claim methodology

Upstream source 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.

Quoted source text, attributed separately from HOL analysis.