CVE-2026-4274

Insufficient authorization in shared channel membership sync grants team-level access instead of channel-level access

State: Published
Severity: 5.4 Medium
Published: Mar 26, 2026
Updated: Mar 26, 2026
Reserved: Mar 16, 2026

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

Scores

CVSS	Score	Vector	Source
3.1	5.4 Medium	CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:N	Mattermost

Weaknesses

CWE-863 Incorrect Authorization

Affected Products

Product	Versions
MattermostMattermost	11.2.0 through 11.2.2Affected 10.11.0 through 10.11.10Affected 11.4.0 through 11.4.0Affected 11.3.0 through 11.3.1Affected 11.5.0Not affected 11.2.3Not affected 10.11.11Not affected 11.4.1Not affected 11.3.2Not affected

References

MMSA-2026-00574vendor-advisory

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