In affected versions of MISP cti-transmute, the conversion-history details endpoint performs an incomplete authorization check. When a history record references a deleted conversion, the associated conversion lookup returns None. The previous logic only denied access when the conversion object existed and the visibility check failed. As a result, deleted conversions bypassed the authorization check and their retained history input/output could be disclosed to a user able to request the corresponding history entry. The July 22, 2026 commit changes the logic to deny access whenever the conversion is missing or the requester lacks permission