CVE-2026-100404 Zulip: Guests can read new messages in non-subscribed public channels
Guest users can read new messages in public channels they are not subscribed to, exposing sensitive communication data.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- None listed
What is CVE-2026-100404?
CVE-2026-100404 is a medium-severity missing authorization vulnerability in zulip, published on 14 Oct 2026. Any signed-in user can exploit it over the network, with no action from the victim.
Official 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.
Weakness: CWE-862
Which versions are affected by CVE-2026-100404?
How do I fix CVE-2026-100404?
No fix has been published for CVE-2026-100404 yet. Limit exposure of the affected software until one is available.
Upgrade, and check permissions on every request on the server, not only in the interface. More about Missing authorization.
Is CVE-2026-100404 being exploited?
There is no known exploitation of CVE-2026-100404 in the wild and no public exploit code.
Sources
Also known as GHSA-5r8f-gq2h-fcgp.