Windows Phone 7 Security Talk at OWASP AppSec Ireland

David Rook

Windows Phone 7 Security

OWASP AppSec Ireland

Friday, 7 September 2012

if (slide == introduction)
System.out.println("I’m David Rook");

• Application Security Lead, Realex Payments, Dublin
CISSP, CISA, GCIH and many other acronyms

• Security Ninja (@securityninja)

• Speaker at developer and security conferences

• Microsoft Developer Security MVP

• SC Magazine Information Security Rising Star 2012

• Developed and released Agnitio and the WPAA


Agenda

• Smartphones and apps - big numbers, little security?

• Windows Phone 7 introduction

• Windows Phone 7 platform security

• Windows Phone 7 application security


Mobile device sales 2011

472 million

Smartphones
31%

Mobile
69%

1.3 billion

Source: http://www.gartner.com/it/page.jsp?id=1924314

Smartphone OS market share 2011
Microsoft
2%

RIM
9%
Symbian
12%
Android
51%

iOS
24%

Source: http://www.gartner.com/it/page.jsp?id=2120015


• Microsoft has 1.9% of the smartphone market share

• Smaller market share than something called Bada




• Should I even continue with this talk about Windows Phone 7?
• Similar approach to Android with many devices available




• IDC predict that they will have 20% market share by 2015




• IDC predict that it will have 20% market share by 2015
• 20% is unlikely but it’s market share will increase in my opinion


Windows Phone 7 Introduction

• The smartphone from Microsoft

• First released in late 2010 with 7 updates since then
• Based on Windows Embedded Compact v6 and v7
• Minimum “tough but fair” hardware requirements
• Apps only available via the Windows Phone Marketplace
• Specifically aimed at the consumer market not enterprise



• .NET Compact Framework

• Version of the .NET framework for resource constrained devices
• Some of the same classes and some mobile specific ones
• Compiler translates your code into Intermediate Language
• Apps are JIT compiled and executed by the .NET CLR
• Only managed .NET code allowed in your apps*


private void button1_Click(object sender, RoutedEventArgs e)
        {
            MessageBox.Show("Hello OWASP AppSec Ireland!");
        }

C# Compiler

Managed
Module

.NET CLR



• Windows Phone 7 Kernel Architecture

• 32bit OS that runs inside a 4GB virtual address space
• 2GB allocated to the kernel and 2GB to process executing
• That isn’t quite true, the process executing only gets 1GB
• 1GB is for components commonly mapped into all processes



• Windows Phone 7 Kernel Architecture
APPLICATIONS
Space
User

TELSHELL.EXE UDEVICES.EXE SERVICESD.EXE CPROG.EXE

COREDLL/WINSOCK/COMMCRL/WININET
kCoreDLL.DLL
KERNEL.DLL
Kernel
Space

FILESYS.DLL Device.DLL
GWES Network
OAL.EXE
FSDMGR.DLL Drivers

Hardware


Process Code
Process
Space
2GB

User DLLs

Memory Mapped Files

GWES
Kernel
Space

Drivers
2GB

File System

Kernel



Shared System Heap
256MB

processes
across all
Common
RAM Backed Mapfiles
256MB
Process
Memory

Shared User DLLs
2GB

512MB

Private to

process
each
Process Space
1GB per process


Windows Phone 7 Platform Security

• Windows Phone 7 Security Model

• Chambers concept to enforce app isolation and least privilege
• The chambers provide a security boundary to restrict the apps
• Four chambers and apps run in one of them
• Three chambers have fixed permission sets
• The fourth chamber is capabilities based



Trusted Computing
Base (TCB)

Elevated Rights Fixed permissions
Chamber (ERC)

Standard Rights
Chamber (SRC)

Least Privileged
Capabilities based
Chamber (LPC)



Trusted Computing
Base (TCB)

• The kernel and kernel-mode drivers run in the TCB chamber
• Allows processes to have unrestricted access to most resources
• The TCB chamber can modify policy and enforce the security model
• Only Microsoft can add signed software to the TCB chamber



Elevated Rights
Chamber (ERC)

• User-mode drivers and services runs in this chamber
• Can access all resources except security policy
• Intended for services and user-mode drivers
• Only Microsoft can add signed software to the ERC chamber



Standard Rights
Chamber (SRC)

• The default chamber for pre-installed MS and OEM applications
• Apps that do not provide device-wide services run in the SRC



Least Privileged
Chamber (LPC)

• The default chamber for all non-Microsoft applications
• Least Privileged Chambers are configured using capabilities
• Capabilities listed in applications WMAppManifest.xml file



• Windows Phone 7 Application Capabilities

• Application capabilities are features that an app uses
• Apps request permission to access protected APIs during the
deployment process
• Default app manifest file includes a list of all the capabilities*
• WP7 grants security permissions based on the contents of your
WMAppManifest.xml file*
• Not everything your app does needs a capability defined



• Windows Phone 7 Application Capabilities

• Capability checks are enforced at runtime
• Permission set for the apps LPC is created based on the
capabilities
• Requests for other resources == UnauthorizedAccessException
• This exception occurs when the access is attempted not when
the app is executed



• Windows Phone 7 Capabilities Detection Demo



• Windows Phone 7 Application Signing

• Apart from developer unlocked devices apps must be signed
• Microsoft automatically signs approved apps
• Apps must have a valid Microsoft signature to be installed



• Windows Phone 7 Application Sandboxing

• Apps execute within a restricted LPC as we saw earlier
• Cannot communicate with other apps on the phone
• Sandboxed apps aren’t allowed to run in the background
• No access to native code from within the sandbox
• All I/O operations are restricted to per app Isolated Storage



• Windows Phone 7 Application Isolated Storage

• Per app Isolated Storage allows apps to keep data “private”
• Very similar to Isolated Storage in Silverlight
• No direct access to the file system
• No access to other apps Isolated Storage
• Three different ways to use your apps Isolated Storage


Windows Phone 7 Application Security

• Windows Phone 7 Application Security

• Mobile application security introduces almost no new issues
• Forget about specific vulnerabilities for one minute
• Think about the root causes of vulnerabilities, I’ll give you a hand



• Input Validation
• Output Validation
• Error Handling
• Authentication and Authorisation
• Secure Storage
• Secure Communications
• Session Management
• Secure Resource Access
• Auditing and Logging
• Privacy


• Windows Phone 7 Application Security

• Mobile application security introduces almost no new issues
• Forget about specific vulnerabilities for one minute
• Think about the root causes of vulnerabilities, I’ll give you a hand
• From that list what do you think the top 3 are?
• My top 3 are:
• Secure Storage
• Secure Resource Access/Privacy



• OWASP Top 10 Mobile Risks

• I compared the OWASP top 10 mobile risks to my list
• 50% Secure Storage/Secure Communications
• 20% Authentication and Authorisation
• 0% Privacy*



• OWASP Mobile Controls

• Lists the mobile app security controls you should implement
• I compared each control to the list I showed you, guess what?
• 26% Secure Storage
• 16% Secure Communications
• 16% Authentication and Authorisation
• 16% Secure Resource Access*



• My top 3 in the real world

• Secure Storage: Facebook, Citibank, LinkedIn, Google Wallet
• A&A: Foodspotting, Google Wallet, Google (multiple apps)
• SRA/Privacy: Path, Hipster, Ad Libraries
• This doesn’t mean we can ignore all of the other issues



• Preventing the top 3 in your WP7 apps

• I can’t cover every principle in this talk
• With that in mind I'm grouping them to make a "new" top 3
• Data Security - Secure Storage and Communications
• Data Access/Privacy



• Windows Phone 7 Data Security

• Never store data on the device if it really isn’t needed
• WP7 allows us to encrypt data and databases
• Only new databases can be encrypted but very easy to do
• DPAPI is used for file/password/pin etc encryption
• No hashing available and no algorithm selection




• The local database encryption is based on a password
• You create a DB in code and you must include the password
• The database is encrypted using AES-128
• The password is hashed using SHA-256
• An encrypted database can be created with two lines of code



// Create the data context, specify the database ﬁle location and password
DavesDataContext db = new DavesDataContext ("Data Source=isostore:/NinjaSecrets.sdf;Password=NinjaPassword");

// Create an encrypted database after conﬁrming that it does not exist
if (!db.DatabaseExists()) db.CreateDatabase();




• Saving data to an apps isolated storage is not secure
• If you want to encrypt data and not a DB you use the DPAPI
• Use the System.Security.Cryptography.ProtectedData class
• Specifically the Protect() and Unprotect() methods
• Symmetric encryption (AES) used. Hashing isn’t possible




• Every app on a WP7 phone gets its own Encryption Key
• DPAPI generates and securely stores this for you
• Calling Protect() or Unprotect() implicitly selects the apps key
• optionalEntropy parameter can be used to provide extra entropy



• Encrypted Data Code Sample




• Secure Communications is a lot easier!
• Very little to do with the app code itself in my opinion
• More to do with good design and a good security code review!
• Data sent to web services, SQL Azure etc needs protection
• No client side SSL certs allowed and no VPN functionality



• Windows Phone 7 Authentication & Authorisation

• Not just talking about app logon or service authentication
• Specifically talking about access to data on the device
• Gaining users authorisation before accessing sensitive data
• This includes access to users contacts, SMS etc
• I know we already "asked" in the WMAppManifest.xml file....



• Windows Phone 7 Data Access/Privacy

• Another one which isn’t a platform/framework specific
• Understand the data accessed by third party libraries
• Create a privacy policy covering personal data and stick to it!
• Don’t store historical data on the device beyond required time
• Audit app communications to check for data leaks



• The good things

• Shared Windows Core (NT Kernel on a phone)
• Secure boot and Bitlocker on by default
• Enterprise app deployment/management functionality
• OTA updates for all phones for at least 18 months



• The potentially bad things

• Shared Windows Core (NT Kernel on a phone)
• NFC and Wallet Hub
• Native C and C++ code now available to everyone
• Micro SD Card support but with no Bitlocker support


Application Security Workshop

• Free Application Security Workshop at Realex

• 27th September in our Dublin office

• Secure coding: why and how

• Think like a pen tester

• Security focused code reviews


QUESTIONS?
www.securityninja.co.uk
http://sourceforge.net/projects/agnitiotool/

@securityninja

/realexninja

/securityninja

/realexninja


Windows Phone 7 Security Talk at OWASP AppSec Ireland

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