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Description

Mattermost versions 11.3.x <= 11.3.0, 11.2.x <= 11.2.2, 10.11.x <= 10.11.10 fail to use consistent error responses when handling the /mute command which allows an authenticated team member to enumerate private channels they are not authorized to know about via differing error messages for nonexistent versus private channels. Mattermost Advisory ID: MMSA-2026-00588

PUBLISHED Reserved 2026-02-13 | Published 2026-03-16 | Updated 2026-03-16 | Assigner Mattermost




MEDIUM: 4.3CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N

Problem types

CWE-203: Observable Discrepancy

Product status

Default status
unaffected

11.3.0 (semver)
affected

11.2.0 (semver)
affected

10.11.0 (semver)
affected

11.4.0
unaffected

11.3.1
unaffected

11.2.3
unaffected

10.11.11
unaffected

Credits

winfunc finder

References

mattermost.com/security-updates (MMSA-2026-00588) vendor-advisory

cve.org (CVE-2026-21386)

nvd.nist.gov (CVE-2026-21386)

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