Projects/OWASP Mobile Security Project - Security Testing Guide

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Contents

Introduction

A major priority of the OWASP Mobile Security Project is to help standardize and disseminate mobile application testing methodologies. While specific techniques exist for individual platforms, a general mobile threat model can be used to assist test teams in creating a mobile security testing methodology for any platform. The outline which follows describes a general mobile application testing methodology which can be tailored to meet the security tester’s needs. It is high level in some places, and over time will be customized on a per-platform basis.

This guide is targeted towards application developers and security testers. Developers can leverage this guide to ensure that they are not introducing the security flaws described within the guide. Security testers can use it as a reference guide to ensure that they are adequately assessing the mobile application attack surface. The ideal mobile assessment combines dynamic analysis, static analysis, and forensic analysis to ensure that the majority of the mobile application attack surface is covered.

On some platforms, it may be necessary to have root user or elevated privileges in order to perform all of the the required analysis on devices during testing. Many applications write information to areas that cannot be accessed without a higher level of access than the standard shell or application user generally has. For steps that generally require elevated privileges, it will be stated that this is the case.

This guide is broken up into three sections:

  • Prerequisites/Planning- tasks and requirements before conducting the mobile security assessment.
  • Information Gathering- describes the steps and things to consider when you are in the early stage reconnaissance and mapping phases of testing as well as determining the application’s magnitude of effort and scoping.
  • Static Analysis- Analyzing raw mobile source code, decompiled or disassembled code.
  • Dynamic Analysis - executing an application either on the device itself or within a simulator/emulator and interacting with the remote services with which the application communicates. This includes assessing the application’s local interprocess communication surface, forensic analysis of the local filesystem, and assessing remote service dependencies.


How To Use This Resource

As this guide is not platform specific (initially), you will need to know the appropriate techniques & tools for your target platform. The OWASP Mobile Security Project has also developed a tools guide that provides a reference for tools to perform many tasks as well as quick-start guides for many of them. <Link Here>

In this current draft release, the guide is a work in progress. We need additional contributors to help fill in the blanks. If you think something is missing (there certainly is), add it.

The steps required to properly test an Android application are very different than those of testing an iOS application. Likewise, Windows Phone is very different from the other platforms. Mobile security testing requires a diverse skillset over many differing operating systems and a critical ability to analyze various types of source code.

In many cases, a mobile application assessment will require coverage in all three areas identified within this testing reference. A dynamic assessment will benefit from an initial thorough attempt at Information Gathering, some level of static analysis against the application’s binary, and a forensic review of the data created and modified by the application’s runtime behavior.

Please use this guide in an iterative fashion, where work in one area may require revisiting previous testing steps. As an example, after completing a transaction you may likely need to perform additional forensic analysis on the device to ensure that sensitive data is removed as expected and not cached in an undesired fashion. As you learn more about the application at runtime, you may wish to examine additional parts of the code to determine the best way to evade a specific control. Likewise, during static analysis it may be helpful to populate the application with certain data in order to prove or refute the existence of a security flaw.

In the future, contributors to the testing guide should consider adding entries under each section relevant to a specific platform. Over time, OWASP contributors will write platform specific guides and expand upon this body of knowledge.

If a specific area of interest is not covered in this guide, please feel free to either:

  • write the material yourself by registering for a wiki account and contributing content: Wiki Registration
  • bring this up as a topic on the Mobile Project’s mailing list: Mobile Mailing List

Collaboration on building the guide is being performed within Google Docs. You can find the latest and greatest material here: Testing Guide Google Doc

Information Gathering

As a result of this initial information gathering exercise, the tester will be better prepared for the future testing phases. The sad truth is, testers (i.e. Developers, QA & Security) often fail to take the time to learn the target application and supporting infrastructure, opting to dive in blind, possibly losing valuable time and missing possible attack vectors. Without a solid understanding of how the application “should” work as well as the technologies in use, the tester will not be able to identify when the application behaves in a manner that it “shouldn’t”.

Prerequisites of this phase may require specific operating systems, platform specific software development kits (SDK’s), rooted or jailbroken devices, the ability to man-in-the-middle secure communications (i.e. HTTPS) and bypass invalid certificate checks.

  • Proxy and sniff all network traffic from either a physical mobile device or an emulator/simulator. Begin recording and logging traffic (if your proxy tool permits logging, which most should).
  • Register for and/or provision test accounts. Ideally, you will want two accounts per user role to ensure proper testing of vertical and horizontal privilege escalation attack vectors.
  • Manually navigate through the running application to understand the basic functionality and workflow of the application. This can be performed on a real device or within a simulator/emulator.
  • Identify the networking interfaces used by the application
    • 3G/4G
    • Wifi
    • Bluetooth
    • Near Field Communication (NFC)
    • Virtual Private Network (VPN)
  • Is all functionality available over 3G/4G or is wifi required for actions such as data synchronization?
  • What networking protocols are in use? Are secure protocols used where needed? Can they be switched with insecure protocols?
  • Does the application perform commerce transactions?
    • credit card transactions and/or stored payment information.
    • in-app purchasing of goods or features
  • Monitor and identify the hardware components that the application may potentially interact with
    • NFC
    • Bluetooth
    • GPS
    • Camera
    • Microphone
    • Sensors
  • Perform open source intelligence gathering (search engines, source code repositories, developer forums, etc.) to identify source code or configuration information that may be exposed (i.e. 3rd party components integrated within the application)
  • Identify if the application appears to interact with any other applications, services, or data such as:
    • Telephony (SMS, phone)
    • Contacts
    • Google Wallet
    • iCloud
    • Social networks (i.e. Facebook, Twitter, LinkedIn, Google+)
    • Dropbox
    • Evernote
    • Email
  • Can you determine anything about the server side application environment?
    • Hosting provider (AWS, App Engine, Heroku, Rackspace, Azure, etc.)
    • Development environment (Rails, Java, Django, ASP.NET, etc.)
    • Does the application leverage Single Sign On or Authentication APIs (Google Apps, Facebook, iTunes, OAuth, etc.)
    • Any other APIs in use
      • Payment gateways
      • SMS messaging
      • Social networks
      • Cloud file storage
      • Ad networks
  • Perform a thorough crawl of exposed web resources and sift through the requests and responses to identify potentially interesting data or behavior
    • leaking credentials
    • resources not exposed through the UI
    • error messages
    • cacheable information


Static Analysis

There are two primary ways static analysis will generally be performed on a mobile application:

  1. Analyzing source code obtained from development team (prefered)
  2. Using a compiled binary. Some level of static analysis should be performed for both dynamic and forensic analysis, as the application’s code will almost always provide valuable information to the tester (i.e. logic, backend targets, APIs, etc).

In scenarios where the primary goal is to identify programmatic examples of security flaws, your best bet is to review pure source code as opposed to reverse engineering compiled software. For source code reviews, it is highly beneficial to have access to either a development or production instance of any web services. This includes both source code and a working test environment to perform the assessment within in order to expedite understanding of the code.

Getting Started

  • If the source is not directly available, decompile or disassemble the application’s binary
    • extract the application from the device
    • follow the appropriate steps for your platform’s application reverse engineering
    • some applications may require decryption prior to reverse engineering
  • Review the permissions the application requests as well as the resources that it is authorized to access (i.e. AndroidManifest.xml, iOS Entitlements)
  • Are there any easy to identify misconfigurations within the application found within the configuration files? Debugging flags set, world readable/writable permissions, etc.
  • Identify the libraries in use including both platform provided as well as third party. Perform a quick review on the web to determine if these libraries:
    • are up to date
    • are free of vulnerabilities
    • expose functionality that requires elevated privileges (access to location or contact data)
  • Does the application check for rooted/jailbroken devices? How is this done? How can this be circumvented? Is it as easy as changing the case of a file name or path?
  • Determine what types of objects are implemented to create the various views within the application. This may significantly alter your test cases, as some views implement web browser functionality while others are native UI controls only.
  • Is all code expected to run within the platform’s standard runtime environment, or are some files/libraries dynamically loaded or called outside of that environment at runtime?
  • Attempt to match up every permission that the application requests with an actual concrete implementation of it within the application. Often, developers request more permission than they actually need. Identify if the same functionality could be enabled with lesser privileges.
  • Locate hard coded secrets within the application such as API keys, credentials, or proprietary business logic.
  • Identify every entry point for untrusted data entry and determine how it enforces access controls, validates and sanitizes inbound data, and passes the data off to other interpreters
    • from web service calls
    • receiving data from other apps and on-device services
    • inbound SMS messages
    • reading information from the filesystem

Authentication

  • Locate the code which handles user authentication through the UI. Assess the possible methods of user impersonation via vectors such as parameter tampering, replay attacks, and brute force attacks.
  • Determine if the application utilizes information beyond username/password such as
    • contextual information (i.e.- device identifiers, location)
    • certificates
    • tokens
  • Does the application utilize visual swipe or touch passwords vs. conventional usernames and passwords?
    • Assess the method of mapping the visual objects to an authentication string to determine if adequate entropy exists
  • Does the application implement functionality that permits inbound connections from other devices? (i.e.- Wi-Fi Direct, Android Beam, network services)
    • Does the application properly authenticate the remote user or peer prior to granting access to device resources?
    • How does the application handle excessive failed attempts at authentication?
  • Single Sign On
    • OAuth
    • Facebook
    • Google Apps
  • SMS
    • How is the sender authenticated?
      • password
      • header information
    • Are one time passwords (OTP) used or is other sensitive account data transmitted via SMS?
      • Can other applications access this data?
  • Push Notifications
    • If the application consumes information via push notifications, how does the application verify the identity of the sender?

Authorization

  • Review file permissions for files created at runtime
  • Determine if it is possible to access functionality not intended for your role
    • Identify if the application has role specific functionality within the mobile application
    • Locate any potential flags or values that may be set on the client from any untrusted source that can be a point of privilege elevation such as
      • databases
      • flat files
      • HTTP responses
    • Find places within an application that were not anticipated being directly accessed without following the application’s intended workflow
  • Licensing
    • Can licensing checks be defeated locally to obtain access to paid-for data resources? (i.e.- patching a binary, modifying it at runtime, or by modifying a local configuration file)
    • Does the code suggest that licensed content is served with a non-licensed app but restricted by UI controls only?
    • Are licensing checks performed properly by the server or platform licensing services?
    • How does the application detect and respond to tampering?
      • Are alerts sent to and expected by the developer?
      • Does the application fail open or fail closed?
      • Does the application wipe its data?

Session Management

  • Ensure that sessions time out locally as well as server side
  • Is sensitive information utilized within the application flushed from memory upon session expiration?

Data Storage

  • Encryption
    • Are the algorithms used “best of breed” or do they contain known issues?
    • Based on the algorithms and approaches used to encrypt data, do implementation issues exist that degrade the effectiveness of encryption?
    • How are keys managed and stored on the device? Can this reduce the complexity in breaking the encryption?
  • Identify if the application utilizes storage areas external to the “sandboxed” locations to store unencrypted data such as:
    • places with limited access control granularity (SD card, tmp directories, etc.)
    • directories that may end up in backups or other undesired locations (iTunes backup, external storage, etc.)
    • cloud storage services such as Dropbox, Google Drive, or S3
  • Does the application write sensitive information to the file system at any point, such as:
    • credentials
      • username + password
      • API keys
      • authentication tokens
    • payment information
    • patient data
    • signature files
  • Is sensitive information written to data stores via platform exposed APIs such as contacts?

Transport Layer Protection

  • Does the application properly implement Certificate Pinning?
  • Are certificates validated to determine if:
    • the certificate has not expired
    • the certificate was issued by a valid certificate authority
    • the remote destination’s information matches the information within the certificate?
  • Identify if code exist to alter the behavior for traffic transiting different interfaces (i.e.- 3G/4G comms vs. Wi-Fi)? If so, is encryption applied universally across each of them

Information Disclosure

  • Logs
    • Does the application log sensitive information to a globally shared log?
    • Can any of the logged information be considered a privacy violation?
  • Caches
    • predictive text
    • location information
    • Browser cache
  • Exceptions
    • Does sensitive data leak in crash logs?
  • Third Party Libraries and APIs
    • What permissions do they require?
    • Do they access or transmit sensitive information?
    • Can their runtime behavior expose users to privacy issues and unauthorized tracking?
      • by the application

Web Application Issues

  • XSS and HTML Injection
  • Command Injection (if the application utilizes a shell)
  • CSRF
  • SQL Injection
  • Cookies
  • HTML5

Helpful Search Strings and Regular Expressions

Dynamic Analysis