hacking (and defending) iphone applications

Kevin StadmeyerGarrett Held

COPYRIGHT TRUSTWAVE 2011 CONFIDENTIAL

Hacking (and Defending) iPhone Applications


Garrett Held and Kevin Stadmeyer

› Managing Consultants with Trustwave SpiderLabs› Have performed hundreds of application tests from mainframe to web to mobile

Who Are We?


› The Basics› Setup For Testing› Secure Storage of Data And Credentials› Inadvertent Local Storage and Caching› Client Side Sanitization› Secure Coding› Push Notifications› Secure Communications

AgendaWhat we’ll cover – secure coding and beyond, what to look for when assessing an iPhone application


The Basics


Why are people attacking mobile apps?

› Stealing Money› Embarrassing People (“Hactivists”)› Get Famous

Just the Facts, Ma’am


Just the Facts, Ma’amiPhone Apps in the Press


How are people attacking mobile apps?

› New and unsafe operating systems?› Terrible developers who don’t care?› Clueless users who don’t know they should care?



What Security Model We’re Not Talking About?

› Layer 1: Apple Store› Layer 2: Sandboxing via “Seatbelt”



Setting Up The Testing Environment


Don’t you mean setting up the decompiler?

› No

Setting Up The Testing Environment


On das metal – Step 1: get your proxy right

We Built This City


On das metal – Step 2: Get ya certs heard!

We Built This City


On das metal – Step 3: Roll It Up

We Built This City


On das metal – Step 4: Mail it!

We Built This City


On das metal – Step 5: Install It

We Built This City


On das metal – Step 6: Install It (Errrr….)

We Built This City


On das metal – Step 7: Proxy It!

We Built This City


On das metal – Step 8: Victory!

We Built This City


On The Computer Machine – Step 6: Install It!

We Built This City


On The Computer Machine – Step 7: Install It!

We Built This City


On The Computer MachineWe Built This City

› The format is X’<SHA1 Fingerprint>’


Now What?We Built This City


Secure Storage Of Data


The Keychain› Indefinite Storage› Can you store credentials securely without the keychain?– Don’t let the feature make you lazy– Don’t store credentials in the keychain unless you don’t

care about certain things

Storing Credentials


Keychain Compromise via Jailbreaking

› Through a series of steps, retrieves passwords stored in the keychain [1]

› Researchers compromised keychain passwords only, not other protected classes such as passwords for websites– Jailbreak stolen iPhone (requires physical access), gain

SSH access– Copy scripts that will compromise the keychain– Scripts output the victims passwords

Storing Credentials

[1] http://www.sit.fraunhofer.de/en/Images/sc_iPhone%20Passwords_tcm502-80443.pdf


Where Should You Store Them?› Not on the device?– At least not in plaintext!

Storing Credentials


Securely Storing Data At Rest – things to look for

› Database calls?– Injection Possible?

› Using Core Data?– Does the application trust the integrity of the data?– Remember trust boundaries!

Storing Credentials


Recommendations for non-credential data

› Do not store data on the phone if at all possible– Never has it been so easy to lose so much data so fast!

› Require user to enter a passcode– Can still be brute-forced with time once the encrypted

text is found– Poor user-experience on mobile devices

Storing Credentials


Recommendations for non-credential data

› Store decryption key on a server and require credentials (non-stored) to access key– Only works for applications that do not require offline

access– Increases data usage– Revocable though– Data not “stored” in the cloud

Storing Credentials


B-b-b-but kSecAttrAccessibleWhenUnlocked!

› By default iOS writes information to the keychain with this attribute

› By default most user’s passwords suck

Storing Credentials


Look Familiar?Storing Credentials


Most UsersStoring Credentials

Pick Simple PINS10,000 possibilities~.1 second to crack (100k a second is pretty standard)


Protect Stupid UsersStoring Credentials

Require Strong Passwords (8+ alpha-numeric chars)

Use REAL and GOOD encryption Don’t rely on an inherently

insecure PIN to protect users. If they knew what they were

doing we wouldn’t be here today.


Inadvertent Local Storage and Caching


Screenshots› Where are they stored?› When are they taken?› Who can access them!

I Accidently Your Data…


ScreenshotsI Accidently Your Data…


Screenshot ProtectionI Accidently Your Data…


Other Storage Of Information

› Autocomplete, etc.



Autocomplete› Override autocomplete› textfield.autocorrectionType = UITextAutocorrectionNone



Client Side Sanitization


It’s bad…› Less burden on server› Critical bypasses (yay!)

Client Side? More like Bad side, amirite?


It’s bad…› Some classic Web Application faults translate well into the iPhone.

› Web developers relied on:– JavaScript controls– Hidden fields– JSON responses– Information stored in Flash objects



Rogue Clients› Attackers can write apps (Some testers, too)› Client side secrets can be decompiled– We don’t care if it’s obfuscated for now, that’s a

point in time.› Distributed through trusted App store?– Already happened to Android



How To Do It Right› Server Side Controls› Assume everything coming in came from a rouge or compromised client

› Enforce secure communications



What Applies in the iOS world?Client Side? More like Bad side, amirite?

Applies Does Not ApplySQL Injection CSRF*XML Injection XSS*Other InjectionPrivilege EscalationSession HijackingOverflows (Buffer, Integer)Format String Problems Insecure use of SSL


CSRF and XSS In Apps?› Calls to browser– Recent Android Issue [1]– Loads javascript:alert(document.cookie)

› Embedded browser shares web app issues

› Rogue applications and rogue users


]1] http://www.crn.com.au/News/265931,video-details-android-browser-intercept-flaw.aspx


Break That Down Into Attackers ViewClient Side? More like Bad side, amirite?

Attacker Targets Server Attacker Targets DeviceSQL Injection Overflows (Buffer, Integer)XML Injection Format String Problems Other InjectionPrivilege EscalationSession HijackingInsecure use of SSL


What Does This Mean to a Developer?

› Time to throw out any assumptions that the device will protect you by obfuscating anything

› A new set of security practices need to be developed and followed when creating App’s



Shifting Paradigms – we hate ourselves

› Local Storage Review– What is stored and why?

› Educating QA– Proxy testing

› Review Local and Remote Inputs› Information Leakage



Local Storage Review› Review what’s stored on the device by the application

› Review what’s stored on the device by iOS

› Keep it simple, review to remove

A New Methodology


Educating QA› Develop test cases for new and old vulnerabilities

› Formal process for testing communications and settings

A New Methodology


Local And Remote Inputs› User input from Apps is always a concern

› Don’t forget about responses that could be intercepted or hijacked.

› Maintain the integrity of the device.

A New Methodology


Information Leakage› Examine all traffic to / from the application, like should be done with web applications

› Additional examination of what sensitive data may be in the binary.– Is it necessary? Keep it simple. Review to Remove.

A New Methodology


Secure Coding


What Can Go Wrong?› Arbitrary executable code could be loaded and executed on the device

› Bypass “seatbelt”

Buffer Overflow


How To Do It Right› Same concerns as in C› Use appropriate functions [1]– Example: strlcpy NOT strncpy

› Properly calculate buffer size (constants)› Includes integer bounds checking

Buffer Overflow

[1] http://developer.apple.com/library/mac/#documentation/Security/Conceptual/SecureCodingGuide/Articles/BufferOverflows.html


What Can Go Wrong?› Application displays user input (as applications are known to do)

› Uses the [NSString stringWithFormat] method› Uses the printf function› Attacker sends “%s%s%s%s” instead of “Hello”

Format String Attack


How To Do It Right› Enforce Secure Coding Standard– Just like web applications– No vulnerable function should accept untrusted

user input that could be used to determine the format of the output

Format String Attack


What Can Go Wrong?› Application manages state using the deviceID NOT the session ID.

› Sessions not terminated properly on the server side

› Following Conditions– User logged into the application at some point in

the last day and subsequently logged out.– Attacker supplies wrong credentials through the

mobile app.

Race Conditions


What Can Go Wrong?› Following Conditions– Application request “session refresh” while waiting

for the incorrect login response to be sent. – Server “refreshes” the session based on the device

ID.– Application receives a response indicating the login

was successful, followed by a login denied error. – Application subsequently ignores the login denied,

continues using the previous session now tied to the Device ID.

Race Conditions


How To Do It Right› Strong server side controls over access– Policy enforcement on concurrent logins– Do not maintain session via Device ID– Properly Logout Users

› Make sure any mobile applications have the same, proper logic enforcement as web applications.

Race Conditions


What Can Go Wrong?› Just about everything– Logic vulnerabilities– Weak session controls– Classic web application vulnerabilities– Too much trust in the client-side controls

Server Side


How To Do It Right› Harden the server– Every client is treated like it might be malicious

› Use same guidelines as Web Apps– OWASP Secure Development

Server Side


Push Notifications


Real FastPush Notifications

http://www.dhanjani.com/


Secure Communications


SSL Whaaaa?› NSURL method

– iOS is secure by default in regards to SSL certs when using this method to retrieve HTTPS content


Source: http://www.flickr.com/photos/mikebaird/


Well, that’s true now…› SSLizzard

– Exploit developed by SpiderLabs to take advantage of weakness in certificate validation. [1]

– Allowed SSL MITM attacks without errors.– Apple patched this, “This vulnerability has been corrected in versions

5.0b4, 4.3.5, and 4.2.10.”


[1] TWSL2011-007: iOS SSL Implementation Does Not Validate Certificate Chain, https://www.trustwave.com/spiderlabs/advisories/TWSL2011-007.txt


SSL Whaaaa?Secure Communications

Source: http://www.flickr.com/photos/lenore-m/


This Is It


› The Basics› Setup For Testing› Secure Storage of Data And Credentials› Inadvertent Local Storage and Caching› Client Side Sanitization› Secure Coding› Push Notifications› Secure Communications

This Is ItReview


Summary› Testing is easy– For you and for “them”

› Security is hard– Really just for you

› So test everything!

This Is It

hacking (and defending) iphone applications

Documents

city copyright trustwave

maam copyright trustwave

press copyright trustwave

x copyright trustwave

maamcopyright trustwave

trustwave spiderlabshave

metal step

computer machine step