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CVE-2026-28759

Insufficient authorization in shared channel membership sync allows remote cluster to remove users from arbitrary channels PUBLISHED

Description (CNA)

Mattermost versions 11.5.x <= 11.5.1, 10.11.x <= 10.11.13, 11.4.x <= 11.4.3 fail to validate that a remote cluster has access to a channel before processing membership removal requests during shared channel membership sync, which allows a malicious remote cluster to remove any user from any channel, including private channels, via crafted membership sync messages targeting channels the remote cluster is not authorized to access. Mattermost Advisory ID: MMSA-2026-00576

Affected (CNA)

Vendor / productVersions
Mattermost / Mattermostaffected 11.5.0 through 11.5.1; affected 10.11.0 through 10.11.13; affected 11.4.0 through 11.4.3; unaffected 11.6.0; unaffected 11.5.2; unaffected 10.11.14; unaffected 11.4.4

CWE

CWE-863

References

ADP enrichment

CISA-ADP

No English description supplied.

No references supplied.