Respect for human rights is often understood to be in tension with a robust approach to protecting human security (both within a single state’s territory and across territorial boundaries). Principles like those which form the basis of Fox and Criddle’s fiduciary theory of sovereignty—such as non-instrumentalization and non-domination—may suggest an approach to balancing these competing interests, but not necessarily with the specificity and detail required of particular legal contexts. This article seeks to explore an alternative route to balancing these competing interests—one which draws on positive international law. The context for this exploration is that of ‘asymmetrical self-defence,’ taking the quintessential threat to both human rights and human security, in the form of armed conflict, as its case study. Where states provide support to participants in armed conflicts occurring on the territory of other states, they potentially increase the risks to those caught up in the conflict, raising important questions as to the nature, basis and content of the international legal duties associated with their support. It is argued that Common Article 1 of the Geneva Conventions, risk related human rights obligations (like that of non-refoulement) and the Arms Trade Treaty are the positive law basis for obligations Fox and Criddle otherwise characterize as fiduciary. These frameworks provide much more of the detail required for effective regulation, such as obligations to be informed, the permissibility or otherwise of balancing other interests against the risk of IHL breaches, and the differentiated treatment of risks to jus cogens compliance.