Mattermost is grouping calls in the /metrics endpoint by id and reports that id in the response. Since this id is the channelID, the public /metrics endpoint is revealing channelIDs.
{ "nvd_published_at": "2023-12-06T09:15:09Z", "cwe_ids": [ "CWE-200" ], "severity": "MODERATE", "github_reviewed": true, "github_reviewed_at": "2023-12-08T21:57:14Z" }