RTIR's ticket creation forms show the subject of the related ticket when splitting a ticket or creating an incident from a report, and they render that subject without HTML escaping. A ticket subject containing script runs it when a user opens either form. RTIR grants everyone the right to create Incident Reports by default, so an unauthenticated sender of an emailed report can set that subject. The script then runs in the session of the incident handler who creates an incident from the report or splits it, and can act in RT with that user's authority.  The issue was fixed in version 6.0.4. RTIR 5.0 is not affected.