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CVE PROGRAM SOURCE RECORD5.4 Medium

CVE-2026-4274

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

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Status
Published
Published
Updated
Assigning organization
Mattermost

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

Affected products

Version statuses are supplied by the assigning organization. Consult the original record for detailed ranges and platform conditions.

Mattermost Mattermost

Default version status: unaffected

  • 11.2.0 to ≤ 11.2.2affected
  • 10.11.0 to ≤ 10.11.10affected
  • 11.4.0 to ≤ 11.4.0affected
  • 11.3.0 to ≤ 11.3.1affected
  • 11.5.0unaffected
  • 11.2.3unaffected
  • 10.11.11unaffected
  • 11.4.1unaffected
  • 11.3.2unaffected

References