MISP Information Disclosure via Related Events Listing Bypassing Per-Event Authorization

MISP contains an authorization bypass in the related events listing functionality. When a user requests the list of events correlated to a given event, the system retrieved related event metadata directly from the correlation table without re-validating the caller's access rights against each related event. The correlation table stores a snapshot of the event's distribution level and sharing group at the time the correlation was created, and does not carry the published flag. As a result, events that the caller is not permitted to open—because they are unpublished, or because their distribution or sharing group has changed since the correlation was recorded—were still returned with their metadata (title, date, correlating value counts). Preconditions: - An authenticated user with access to at least one event in MISP. - The existence of correlation entries linking that event to other events the user should not be able to view. Impact: - Unauthorized disclosure of event metadata (titles, dates, correlation counts) for events the user has no right to access. - Potential reconnaissance of threat-intelligence event names and timelines across sharing groups. Affected: MISP versions prior to the fix commit (2ffa97f05).