Violence against humanitarians is a commonplace phenomenon in contemporary armed conflict. This paper examines how the manipulation of international legal principles for political or military purposes, practice known as 'lawfare', impacts humanitarian security in conflict-affected areas. Drawing on a case study of the Syrian conflict (2011-ongoing), it finds that lawfare has been used to legitimate systematic civilian targeting by pro-government forces and to delegitimise aid delivery to opposition-held areas of the country. Efforts to use legal measures to promote civilian welfare-by way of sanctions or demands for cross-border humanitarian access-have been taken as evidence of Western attempts to politicise humanitarian considerations and international law. In practice, this has meant increased security risks for aid workers and impunity for those implicated in the violence.