A Systematic Study of Android Non-SDK (Hidden) Service API Security

TL;DR

This paper systematically investigates the security vulnerabilities of Android's non-SDK hidden APIs, analyzing Google's countermeasures and developing a static analysis tool to identify inconsistencies and potential exploits across Android versions 6 to 12.

Contribution

It introduces ServiceAudit, a static analysis tool that detects security enforcement inconsistencies in Android's hidden APIs, providing a comprehensive vulnerability analysis across multiple Android versions.

Findings

112 vulnerabilities found in Android 6 with high precision

Over 25 hidden APIs with inconsistent protections in Android 11 and 12

Only one API in Android 11 poses severe security risk, none in Android 12

Abstract

Android allows apps to communicate with its system services via system service helpers so that these apps can use various functions provided by the system services. Meanwhile, the system services rely on their service helpers to enforce security checks for protection. Unfortunately, the security checks in the service helpers may be bypassed via directly exploiting the non-SDK (hidden) APIs, degrading the stability and posing severe security threats such as privilege escalation, automatic function execution without users' interactions, crashes, and DoS attacks. Google has proposed various approaches to address this problem, e.g., case-by-case fixing the bugs or even proposing a blacklist to block all the non-SDK APIs. However, the developers can still figure out new ways of exploiting these hidden APIs to evade the non-SDKs restrictions. In this paper, we systematically study the vulnerabilities due to the hidden API exploitation and analyze the effectiveness of Google's countermeasures. We aim to answer if there are still vulnerable hidden APIs that can be exploited in the newest Android 12. We develop a static analysis tool called ServiceAudit to automatically mine the inconsistent security enforcement between service helper classes and the hidden service APIs. We apply ServiceAudit to Android 6~12. Our tool discovers 112 vulnerabilities in Android 6 with higher precision than existing approaches. Moreover, in Android 11 and 12, we identify more than 25 hidden APIs with inconsistent protections; however, only one of the vulnerable APIs can lead to severe security problems in Android 11, and none of them work on Android 12.