Mattermost versions 10.11.x <= 10.11.9 fail to properly validate channel membership at the time of data retrieval which allows a deactivated user to learn team names they should not have access to via a race condition in the /common_teams API endpoint.. Mattermost Advisory ID: MMSA-2025-00549

CVSS Details

CVSS 3.1 Base Score: 3.1
CVSS 3.1 Vector: (CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:L/I:N/A:N)

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CVE-2026-20796: Time-of-check Time-of-use (TOCTOU) Race Condition

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