Improper access control in Zulip Server - #VU151561
Published: September 22, 2026
Vulnerability identifier: #VU151561
CSH Severity: Low
CVSS v4: 5.3 [CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:L/VI:N/VA:N/SC:N/SI:N/SA:N]
CVE-ID: N/A
CWE-ID: CWE-284
Exploitation vector: Remote access
Exploit availability:
No public exploit available
Vulnerability details
The vulnerability allows a remote user to disclose sensitive information.
The vulnerability exists due to improper access control in UserTopic row handling during channel moves when moving messages from a public channel to an inaccessible private channel. A remote user can move messages to a private channel to disclose private channel topic metadata.
The issue requires a non-subscriber to have a UserTopic row from muting or following the topic in the public channel.
Affected software
Zulip Server
Remediation
Install security update from vendor's website.
Zulip Server - update to 12.3