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Description

Mattermost versions 11.2.x <= 11.2.2, 10.11.x <= 10.11.10, 11.4.x <= 11.4.0, 11.3.x <= 11.3.1 fail to restrict team-level access when processing membership sync from a remote cluster, which allows a malicious remote cluster to grant a user access to an entire private team instead of only the shared channel via sending crafted membership sync messages that trigger team membership assignment. Mattermost Advisory ID: MMSA-2026-00574

PUBLISHED Reserved 2026-03-16 | Published 2026-03-26 | Updated 2026-03-26 | Assigner Mattermost




MEDIUM: 5.4CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:N

Problem types

CWE-863: Incorrect Authorization

Product status

Default status
unaffected

11.2.0 (semver)
affected

10.11.0 (semver)
affected

11.4.0 (semver)
affected

11.3.0 (semver)
affected

11.5.0
unaffected

11.2.3
unaffected

10.11.11
unaffected

11.4.1
unaffected

11.3.2
unaffected

Credits

daw10 finder

References

mattermost.com/security-updates (MMSA-2026-00574) vendor-advisory

cve.org (CVE-2026-4274)

nvd.nist.gov (CVE-2026-4274)

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