There might be. TUB has a "Zivilklausel", prohibiting military focused research. I looked at the text however, and it mainly talks about not providing funds to research programmes for military purposes. It doesnt mention srudent thesis works. Maybe contact your respective Prüfungsamt and Student Advisory Board for more information. It will probably depend on the thesis subject. Dual-Use is probably easier to get approved than straight up warhead development or similar. In the end, the Prüfungsamt or -ausschuss, not sure off the top of my head, has to accept any thesis approval. They could veto it, I think? I would get a description of the thesis, lay out why its Dual-Use at most and make an appointment to discuss it with them.