CVE-2026-3636: Mattermost doesn't sanitize team member data when returned via API to users without elevated permissions

May 26, 2026 (updated June 26, 2026)

Mattermost versions 11.6.x <= 11.6.0, 11.5.x <= 11.5.3, 11.4.x <= 11.4.4, 10.11.x <= 10.11.14 fail to sanitize team member data when returned via API to users without elevated permissions which allows a user without permissions to get data about team members roles via invoking various team API endpoints. Mattermost Advisory ID: MMSA-2026-00626.

References

github.com/advisories/GHSA-ffpr-pfr4-g354
mattermost.com/security-updates
nvd.nist.gov/vuln/detail/CVE-2026-3636

Code Behaviors & Features

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