CVE-2026-16047
MediumCVSS 4.3Exploitation Probability (EPSS)
Low risk6th percentile - higher than 6% of all known CVEs
Summary
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.
Risk Assessment
The risk includes disclosure of private channel membership information, potentially compromising confidentiality of organizational communication.
Recommendation
Upgrade Mattermost to a version that fixes this vulnerability (as per vendor recommendations).
Original NVD description (English source)
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