COVERT is a tool that analyzes Android applications in a compositional manner to detect security vulnerabilities that occur due to the interaction of apps. It extracts models of individual apps and the Android framework and uses the Alloy analyzer to check the models for vulnerabilities. An evaluation on over 500 real-world apps found that COVERT can effectively detect inter-app vulnerabilities in minutes and does not require source code. It was implemented with desktop, mobile, and web-based front-ends to facilitate end-user analysis of apps.

1. M.Tech (CSE) 1st semester

2. ABSTRACT
• Problem: Enforcement of the permissions in Android is at the
level of individual apps, allowing multiple malicious apps to
collude and combine their permissions or to trick vulnerable
apps to perform actions on their behalf that are beyond their
individual privileges.
• Research efforts are subject to a common limitation: they are
intended to detect and mitigate vulnerabilities in a single app.
• COVERT’s analysis is modular and it statically analyzes the
reverse engineered source code of each individual app, and
extracts relevant security specifications in a format suitable for
formal verification.
• Using COVERT to examine over 500 real-world apps
corroborates its ability to find inter-app vulnerabilities in bundles
of some of the most popular apps on the market.

3. INTRODUCTION• Previous techniques failed to identify vulnerabilities due to the interaction
of multiple apps, such as collusion attacks and privilege escalation
chaining, which cannot be detected by analyzing a single app in isolation.
• COVERT increases the scope of application analysis This enables reasoning
about the overall security posture of a system.
• The main objective of COVERT is to automatically
– identify such vulnerabilities that occur due to the interaction of apps
comprising a system
– by inferring the security properties from individual apps and checking
them as a whole by means of formal analysis
– determine whether it is safe for a bundle of apps, requiring certain
permissions and interacting with each other, to be installed together.
• COVERT extracts essential information and captures them in an analyzable
formal specification language and uses Alloy as a specification language,
and the Alloy Analyzer as the analysis engine.

4. Android Overview
Application Components
Components are basic logical
building blocks of Android
applications. There are four
types of components:
• Activity
• Service
• Broadcast Receiver
• Content Provider
IPC
Android depends app insulation to
protect apps requires interactions
to occur through a message
passing mechanism, called inter-
process communication. IPC is
conducted by means of Intent
messages.
Application Configuration
Each Android application must declare
upfront its configuration.
Component capabilities are
specified as a set of Intent Filters
that represent the kinds of
requests a given component can
respond to.
Permissions
Each application must declare as part of
its manifest the permissions it
requires, and the Android system
prompts the user for consent during
the application installation.
Android platform provides over 130 pre-
defined permissions, and apps can
also define their own permissions.
Intent Messages
Intent message is an event for
an action to be performed
along with the data that
supports that action.
Sandboxing
Sandboxing is a computer security term
referring to when a program is set
aside from other programs in a
separate environment so that if
errors or security issues occur,
those issues will not spread to
other areas on the computer.

5. Literature survey
• Main focus of work is on performing program analysis over Android applications for
security and Android’s permissions and their use across applications. All the research
work have never been evaluated over real-world applications.
• FlowDroid introduces a precise approach for static taint flow analysis for each app
component. SCanDroid statically analyzes data flows to detect permission
inconsistencies between apps that could possibly allow malicious access to sensitive
information. It requires the source code of applications.
• TaintDroid detects information leak vulnerabilities using dynamic taint flow
analysis at the system level. IPC Inspection prevents privilege escalation at OS level.
Whyper is a tool that checks the app’s requested permissions against its
description, enabling the user to determine if certain requested permissions are
suspicious.
• Pscout is used to extract the permission specification from the Android OS source code
using static analysis, leading to a comprehensive set of permission maps.

6. Architecture
COVERT
Parts
Model Extractor
Formal Analyzer
Models
App model
Android
Framework
spec.

7. Example scenario
A malicious app exploits the vulnerabilities of two other apps to send the device
location data to the desirable phone number

9. Entity
Extraction
and
Resolution
Control Flow
Augmentation
Vulnerable
Path
Identification
Static analysis
technique
• Input as APK and app byte code
• Generate app models (build on top of Soot
and Dexpler)
Check for
vulnerability
• Combine with formal spec of app
framework
• Alloy as specification language
• Report of list of vulnerabilities
Method of Implementation
1. MODEL EXTRACTOR
We first need a model of each app to determine
the inter-process communications and the
security properties.
A model for an Android application is a tuple
A = <C, I, F, P,S >, where
•C is a set of components, set of Intent messages, Intent filters, permissions and set of sensitive paths
•I is a set of event messages that can be used for both inter- and intra-app communications.
•If component is non-empty, the Intent is called an explicit Intent, as the recipient is given explicitly.
•F is a set of Intent Filters, describes an interface of c in terms of Intents that it can handle.
•P is a union of required (Preq) and enforced permissions(Penf)
•S is a finite set of vulnerable paths

10. Model Extractor

12. Formal Analyzer
Alloy Overview
Formal Model of
Android Framework
Formal Model of Apps
Checking Android
Application models
There are four main reasons for choosing
Alloy:
1. Its comprehensible, object-oriented-
like syntax, makes it useful for declarative
specification of both apps and properties
to be checked.
2. Ability to automatically analyze
specifications with no custom
programming is useful as an automation
mechanism.
3. Effective module system allows us to
split the overall, complicated system model
among several tractable modules.
4. The extraction approach to generate
bundle specifications is incremental. Once
an app model is extracted, it can be reused
for analysis within several bundles of apps.

13. Formal Model of Android Framework
The analyzer provides two types of
analysis: Simulation, in which the
analyzer demonstrates consistency of
model specifications by generating a
satisfying model instance;
Model Checking, which involves
finding a counterexample a model
instance that violates a particular
assertion.
There are six top-level signatures to
model the basic element types:
Application, Component, Intent
Filter, Intent, Path, and Permission.
These signatures are defined as
abstract, meaning that they cannot have
an instance object without explicitly
extending them.

14. Formal model of apps
Three pieces of Alloy
specifications are conjoined in
the process of modeling various
parts of Android apps extracted
from their APK files.
1. Specification module called
appDeclaration
2. App model, represented in a separate
Alloy module for each app.
3. Inter-process communication module
that models all Intent messages created
within app.

15. Checking Android Application models
Considering the privilege escalation,
Davi et al state it as follows:
“An application with less permissions (a
nonprivileged caller) is not restricted to
access components of a more privileged
application (a privileged callee).”
The assertion states that the dst
component (victim) has access to a
permission (uses Permission) that is
missing in the src component
(malicious), and that permission is not
being enforced in the source code of
the victim component, nor by the
application embodying the victim
component.

16. Benefits
• COVERT can effectively detect inter-app vulnerabilities in few
minutes.
•Our prototype implementation of the approach only requires the
availability of Android executable files, and not the original source code.
•COVERT, can be used not only by developers, but also by end-users as
well as third-party reviewers.
•COVERT is implemented as a publicly available tool. We have built a
prototype implementation of the model extractor component on top of the
Soot static analysis tools for analyzing Java byte code. We use Dexpler
transformer to translate Android’s dalvik bytecode into the Soot’s
intermediate representation language, called Jimple.
•All the research work have never been evaluated over real-world
applications.

17. Mobile and Web-based applications
These work together to analyze the
installed apps in a mobile device
and generate the vulnerability
report.
Applications

18. Desktop Client
Desktop Client is a JavaFX application that provides a graphical user
interface and enables end-users to analyze a set of APK files,
which could be downloaded from online app stores such as
Google Play.

19. Result Analysis
To assess the effectiveness of our approach in revealing Android inter-app
vulnerabilities, we have conducted an evaluation that addresses the following
research questions:
RQ1. What is the importance of this research? To what extent are Android apps
over privileged and unsafe due to usage of permission-required APIs?
RQ2. How well does COVERT perform? Does it enable compositional analysis
of real-world Android apps? How much manual effort is involved in the
analysis process?
RQ3. What is the overall accuracy of COVERT in detecting inter-app
vulnerabilities?
RQ4. How does compositional analysis compare to single app analysis?
RQ5. What is the performance of our prototype tool implemented atop SAT
solving technologies and static analyzers?

20. Scatter plot for analysis time for model
extraction of Android apps.

21. COVERT, a tool that analyzes Android applications in a
compositional manner to detect inter-app and inter-
component security vulnerabilities.
COVERT comes with desktop, mobile and web-based
front-end applications that facilitate the end-user
interactions with the analysis engine.
The experimental results corroborated its ability to reveal
inter app vulnerabilities in real-world Android apps, many of
which were previously unknown.
Conclusion
•COVERT can be extended, and significant components of it reused, for detecting other
types of inter-app vulnerabilities, like application collusion and information leakage.
For this, COVERT’s program analysis needs to be extended to take information flow into
account for Android apps.
•COVERT can be extended with dynamic analysis techniques which can be used to
address vulnerabilities in native code. Android Apps may include native code in addition
to Java code, in the form of a Java Native Interface (JNI) library, which cannot be
sufficiently addressed through static analysis techniques.
future work

22. 1. H. Bagheri, A. Sadeghi, J. Garcia, and S. Malek, “Covert: Compositional analysis of
android inter-app vulnerabilities,” George Mason University, Tech. Rep.
2. K. W. Y. Au, Y. F. Zhou, Z. Huang, and D. Lie, “Pscout: Analyzing the android
permission specification,” in Proceedings of CCS, 2012.
3. D. Jackson, “Alloy: a lightweight object modelling notation,” TOSEM,vol. 11, no. 2
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5. L. Davi, A. Dmitrienko, A.-R. Sadeghi, and M. Winandy, “Privilege escalation attacks
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Inter-Component Communication Mapping in Android with Epicc:An Essential Step
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references

23. Vulnerability is not weakness. And
that myth is profoundly dangerous.
Vulnerability is the birthplace of
innovtion, creativity and change.
-Brene Brown