The Skeleton Keys: A Large Scale Analysis of Credential Leakage in Mini-apps

—In recent years, the app-in-app paradigm, involving super-app and mini-app, has been becoming increasingly popular in the mobile ecosystem. Super-app platforms offer mini-app servers access to a suite of powerful and sensitive services, including payment processing and mini-app analytics. This access empowers mini-app servers to enhance their offerings with robust and practical functionalities and better serve their mini-apps. To safeguard these essential services, a credential-based authentication system has been implemented, facilitating secure access between super-app platforms and mini-app servers. However, the design and workflow of the crucial credential mechanism still remain unclear. More importantly, its security has not been comprehensively understood or explored to date. In this paper, we conduct the first systematic study of the credential system in the app-in-app paradigm and draw the security landscape of credential leakage risks. Consequently, our study shows that 21 popular super-app platforms delegate sensitive services to mini-app servers with seven types of credentials. Unfortunately, these credentials may suffer from leakage threats caused by malicious mini-app users, posing serious security threats to both super-app platforms and mini-app servers. Then, we design and implement a novel credential security verification tool, called KeyMagnet, that can effectively assess the security implications of credential leakage. To tackle unstructured and dynamically retrieved credentials in the app-in-app paradigm, KeyMagnet extracts and understands the semantics of