Permission re-delegation: attacks and defenses

TLDR

Modern browsers and smartphone operating systems isolate applications and require user permission for privileged access, but inter‑application communication can enable permission redelegation. The study aims to expose the risks of permission redelegation through real‑world attacks on Android system apps and to propose IPC Inspection as a defense. Permission re‑delegation occurs when a privileged app performs tasks for a less‑privileged one, and IPC Inspection mitigates this by stripping privileges upon receiving IPC from a lower‑privileged app. Implementation of IPC Inspection on a browser and Android successfully blocks the identified permission‑redelegation attacks.

Abstract

Modern browsers and smartphone operating systems treat applications as mutually untrusting, potentially malicious principals. Applications are (1) isolated except for explicit IPC or inter-application communication channels and (2) unprivileged by default, requiring user permission for additional privileges. Although inter-application communication supports useful collaboration, it also introduces the risk of permission redelegation. Permission re-delegation occurs when an application with permissions performs a privileged task for an application without permissions. This undermines the requirement that the user approve each application's access to privileged devices and data. We discuss permission re-delegation and demonstrate its risk by launching real-world attacks on Android system applications; several of the vulnerabilities have been confirmed as bugs. We discuss possible ways to address permission redelegation and present IPC Inspection, a new OS mechanism for defending against permission re-delegation. IPC Inspection prevents opportunities for permission redelegation by reducing an application's permissions after it receives communication from a less privileged application. We have implemented IPC Inspection for a browser and Android, and we show that it prevents the attacks we found in the Android system applications.