Illegal migration of Afghan nationals to Iran represents one of the most significant national challenges for Iran. It also serves as a contentious issue in the relationship between Iran and Afghanistan, while simultaneously exposing these migrants to various vulnerabilities. The primary objective of this study is to examine the challenges faced by undocumented Afghan migrants within a social process framework. Using a grounded theory approach, this research was conducted through semi-structured interviews with Afghan migrants residing in Tehran. A total of 21 participants were selected via purposive sampling until theoretical saturation was reached. Data analysis was performed using a three-step coding process (open, axial, and selective coding), resulting in the identification of 180 concepts, 25 subcategories, and, ultimately, 5 core categories derived from the relationships between subcategories: imposed constraints, unlawful actions, and high-risk experiences (as conditions); multidimensional deprivation (as consequences); adaptability (as strategies); and life in the shadows (as the central phenomenon). The overall findings of this research indicate that undocumented Afghan migrants in Tehran face multifaceted and high-risk challenges, pushing their lives to the margins of society. To mitigate these challenges, effective policies are required to manage legal migration, block illegal migration routes, and combat trafficking networks. Additionally, improving living conditions, regularizing the status of migrants, and providing opportunities for adaptation can contribute to reducing social harm.