Mattermost versions 9.9.x <= 9.9.0 and 9.5.x <= 9.5.6 fail to validate the source of sync messages and only allow the correct remote IDs, which allows a malicious remote to set arbitrary RemoteId values for synced users and therefore claim that a user was synced from another remote.
{ "cpes": [ "cpe:2.3:a:mattermost:mattermost_server:*:*:*:*:*:*:*:*", "cpe:2.3:a:mattermost:mattermost_server:9.9.0:*:*:*:*:*:*:*" ], "severity": "Medium" }