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Description

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

PUBLISHED Reserved 2026-01-15 | Published 2026-02-13 | Updated 2026-02-13 | Assigner Mattermost




LOW: 3.1CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:L/I:N/A:N

Problem types

CWE-367: Time-of-check Time-of-use (TOCTOU) Race Condition

Product status

Default status
unaffected

10.11.0 (semver)
affected

11.3.0
unaffected

10.11.10
unaffected

Credits

Juho Forsén finder

References

mattermost.com/security-updates (MMSA-2025-00549) vendor-advisory

cve.org (CVE-2026-20796)

nvd.nist.gov (CVE-2026-20796)

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