CVE-2026-19541 — Outgoing OAuth connection client secret exposure during connection validation

Mattermost versions 11.9.x through 11.9.1, 11.8.x through 11.8.5, 11.7.x through 11.7.10, and 11.10.x through 11.10.1 fail to require re-entry of the stored client secret when validating an outgoing OAuth connection.