CVE-2026-16047: Board channel linking without read channel permission validation
Mattermost versions 11.7.x <= 11.7.6, 10.11.x <= 10.11.21, 11.8.x <= 11.8.3 fail to validate that users have read access to a channel before linking a board to it, which allows an authenticated attacker to discover the membership of private channels on the same team via creating, patching, importing, or bulk-creating boards with an arbitrary channelId. Mattermost Advisory ID: MMSA-2026-00674
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
- Upgrade
Upgrade
Mattermostto a version that resolves this vulnerability.Fixed in 11.9.0 - Upgrade
Upgrade
Mattermostto a version that resolves this vulnerability.Fixed in 11.7.7 - Upgrade
Upgrade
Mattermostto a version that resolves this vulnerability.Fixed in 10.11.22 - Upgrade
Upgrade
Mattermostto a version that resolves this vulnerability.Fixed in 11.8.4
Event History
Frequently Asked Questions
What is the severity of CVE-2026-16047?
The severity of CVE-2026-16047 is medium with a score of 4.3.
How do I fix CVE-2026-16047?
To fix CVE-2026-16047, upgrade Mattermost to versions 11.7.7, 10.11.22, or 11.8.4 or later.
What are the implications of CVE-2026-16047?
CVE-2026-16047 allows authenticated attackers to discover the membership of private channels by linking boards without proper permission validation.
Which Mattermost versions are affected by CVE-2026-16047?
Mattermost versions 11.7.x up to 11.7.6, 10.11.x up to 10.11.21, and 11.8.x up to 11.8.3 are affected by CVE-2026-16047.
What type of vulnerability is CVE-2026-16047?
CVE-2026-16047 is a vulnerability related to improper access control in Mattermost's board channel linking functionality.