Improper access control in Zulip Server - #VU151559
Published: September 22, 2026
Vulnerability identifier: #VU151559
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 user IDs and email addresses of users they are not permitted to access.
The vulnerability exists due to improper access control in the direct-message typing notification endpoint when sending a typing notification to an inaccessible user. A remote user can send a typing notification addressed to an inaccessible user to disclose user IDs and email addresses.
The issue affects organizations configured to limit which users guests can see; email addresses are exposed only when the targeted user's email visibility setting permits guest access.
Affected software
Zulip Server
Remediation
Install security update from vendor's website.
Zulip Server - update to 12.3