CVE-2026-3115: Guest users can view group member IDs without respecting view restrictions
Mattermost versions 11.2.x <= 11.2.2, 10.11.x <= 10.11.10, 11.4.x <= 11.4.0, 11.3.x <= 11.3.1 fail to apply view restrictions when retrieving group member IDs, which allows authenticated guest users to enumerate user IDs outside their allowed visibility scope via the group retrieval endpoint.. Mattermost Advisory ID: MMSA-2026-00594
Affected Software
Remediation
Information
Event History
Frequently Asked Questions
What is the severity of CVE-2026-3115?
CVE-2026-3115 has been assessed to have a medium severity due to potential unauthorized access to user IDs by guest users.
How do I fix CVE-2026-3115?
To fix CVE-2026-3115, upgrade Mattermost to a version higher than 11.2.2, 10.11.10, 11.4.0, or 11.3.1.
Who is affected by CVE-2026-3115?
CVE-2026-3115 affects Mattermost versions 11.2.x up to 11.2.2, 10.11.x up to 10.11.10, 11.4.x up to 11.4.0, and 11.3.x up to 11.3.1.
What are the risks associated with CVE-2026-3115?
The risks associated with CVE-2026-3115 include the potential for guest users to enumerate and access sensitive user IDs.
Is there a workaround for CVE-2026-3115 until a fix is applied?
There is no specific workaround for CVE-2026-3115; the recommended action is to upgrade to a secure version.