Android Security Basics: Keeping Users & Apps Safe

1. Android Security Basics How to keep your users and apps safe

2. About Me • Android Developer at ADT

3. Main Areas We are Covering • Data Transmission Security • Data Storage Security • APK Security

4. Data Transmission Security • Inter Process/Component Communication • The Android Security Model • Broadcast permissions • Content Provider Permissions • Safe Network usage • SSL/ PKI Overview • SSL pain points • Pinning • Misc. • WebView pitfalls

5. Android Security Model: Each App is a Linux User

6. Interposes communication Mostly through intents Also Binding Messaging etc Image source http://css.csail.mit.edu/6.858/2012/readings/android.pdf

7. Permissions • Protection levels • normal • dangerous • signature • signature or system – Not allowed in 3rd party apps • For internal only components exported=false For a more in-depth discussion of permissions read http://www.cs.berkeley.edu/~emc/papers/android_permissions.pdf and http://css.csail.mit.edu/6.858/2012/readings/android.pdf

8. Example Insecure Broadcast Receiver • <receiver • android:name="Your receiver” • <intent-filter> • <action android:name=“com.example.mybroadcast"/> • </intent-filter> • </receiver> • Q: Who can send this receiver broadcasts? Any component which uses <intent-filter> before android 4.2 is exported by default

9. <receiver android:name=".MyListener”> <intent-filter> <action android:name= "android.provider.Telephony.SMS_RECEIVED" /> </intent-filter> </receiver> Couldthis permission bebetter? Add <receiver android:name=".MyListener" android:permission="android.permission.READ_SMS">

10. Broadcasts can also put permissions on intents • Intent intent = new Intent(); • intent.setAction(MY_BROADCAST_ACTION); • sendBroadcast(intent,"android.provider.Telephony.SMS_RECEIVED");

11. Content Provider • <providerandroid:name=”com.example.testprovider • android:read_permissions = “android.provider.Telephony.SMS_RECEIVED” • android:write_permissions = “android.provider.Telephony.SMS_RECEIVED” • </provider> • Warning before 4.2 all content providers were exported by default!

12. uri-permissions • <providerandroid:name=”com.example.testprovider" • android:authorities=“" • android:grantUriPermission="true” •           <grant-uri-permissionandroid:pathPattern="/notes/" /> • </provider> • Uri uri = Uri.parse("content://com.example.testprovider/notes/1"); •         Intent intent = new Intent(); • intent.setAction(NOTE_ACTION_VIEW); // SET CUSTOM INTENT ACTION • intent.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK); • intent.addFlags(Intent.FLAG_GRANT_READ_URI_PERMISSION); • intent.setData(uri); • startActivity(intent) See Jason Wei’s http://thinkandroid.wordpress.com/2012/08/07/granting-content-provider-uri-permissions/ for more details

13. Implicit Intent Attacks Broadcast Eavesdropping Broadcast Denial of Service for ordered broadcasts Activity/Service Hijacking Image source: http://www.eecs.berkeley.edu/~emc/papers/mobi168-chin.pdf

14. Target Version Gotachas • If a permission has been added since the target in your androids manifest Android will automatically apply the new permission request to the app's manifest • You can see permission changes at each release • http://developer.android.com/reference/android/os/Build.VERSION_CODES.html

15. SSL Image source: http://www.awghost.com/ssl.html

16. SSL and the Public Key Infrastructure http://software-engineer-tips-and-tricks.blogspot.com/2012/09/what-is-pki.html

17. SSL Pain points • There are A LOT of trust anchors • Vary by Android version and manufacturer • Occasionally get hacked (TurkTrust) • Internal Servers • Download manager doesn’t support SSL before ICS Alvinjs has suggested a custom download manager which can handle ssl at at https://github.com/alvinsj/android-https-downloadmanager-demo

18. How to View Trusted Cas per Phone • ICS onwards, go to Settings->Security->Trusted credentials • Before ICS • adb pull /system/etc/security/cacerts.bks` • keytool -keystore cacerts.bks -storetype BKS -provider org.bouncycastle.jce.provider.BouncyCastleProvider -storepass changeit -v –list *OnionKit offers a consistent set of CAs based on Debian but is requires adding its library to your app. http://commonsware.com/blog/2013/03/07/ssl-android-onionkit.html

19. Anti-Pattern! Accept all certificates SSLSocketFactory.ALLOW_ALLHOSTNAME_VERIFIER Or TrustManager where checkServerTrusted() always returns true An Oct. 2012 study found that 8% of the most popular app on the app store were vulnerable to man in the middle attacks http://www2.dcsec.uni-hannover.de/files/android/p50-fahl.pdf Image: https://www.owasp.org/index.php/Man-in-the-middle_attack

20. Not Registered with CA • AFTER ICS: • Just add the your own certificate to list of trusted CA • BEFORE ICS: • Create a dynamic TrustManager • Store new public certificate in app • Uses system default TrustManager for most checks • If check fails then uses custom TrustManager *For more info about dynamic TrustManager http://nelenkov.blogspot.com/2011/12/using-custom-certificate-trust-store-on.html Or http://commonsware.com/blog/2013/03/04/ssl-android-basics.html Or http://stackoverflow.com/questions/2642777/trusting-all-certificates-using-httpclient-over-https/6378872#6378872 (response by emmby) Ps Certificates don’t have to be expensive. Check out http://webdesign.about.com/od/ssl/tp/cheapest-ssl-certificates.htm

21. Kitkat SSL improvements • SSL CA Certificate Warnings • Android Certificate Pinning for Google Certs http://www.xda-developers.com/android/android-4-4-security-enhancements/

22. Webview Pitfalls • If you are using webviews try to setJavascriptEnabled(false) • addJavaScriptInterface() • If you are sending sensitive information clearCache() afterwards to delete local files • You can also do this serverside with no-cache headers

23. Storing DATA • Public data areas • Database security • Encryption

24. Do you Have To Store it?

25. Public Data areas • All Logs • Any files MODE_WORLD_* • Data on SD cards If you must store large amounts of data in public storage consider encrypting it. Facebook has a new fast encryption library that might be worth looking at http://facebook.github.io/conceal/

26. SQL Injection Attacks http://xkcd.com/327/

27. SQL Injection Example

28. IF you must use a RAW Query • Be sure to sanitize your inputs! • Quotes are not the only problems. • Cleaver attacks using spaces • comments • Strange ascii characters • Things we haven’t thought of yet • Use allowed characters vs disallowed characters if possible. • http://ha.ckers.org/sqlinjection/

29. Store hashes not passwords http://www.unixwiz.net/techtips/iguide-crypto-hashes.html

30. Encryption Gotchas • Before Jellybean 4.2 • secureRandom.setSeed(b) • replaces, not supplements, the existing seed. • So it produced a deterministic number • In Jellybean 4.1-4.3 • the securerandom isn’t guaranteed to give you a random number unless you implement the fix in Some-Securerandom-thoughts To read more about the http://android-developers.blogspot.co.uk/2013/08/some-securerandom-thoughts.html And http://blog.k3170makan.com/2013/08/more-details-on-android-jca-prng-flaw.html

31. Keystore • See Code

32. APK Security • Application Signing • How does signing work? • Master Key Exploit • Tamper detection • Decompiling • How an APK gets built/ What’s in an APK? • Demo of Decompiling an APK • Progaurd • What is still visible even after obfuscation?

33. App signing • purpose of certificates in Android is to distinguish application authors • Android won't allow application to be upgraded unless signed with same certificate the applications are signed with the same key. • Android allows applications that are signed with the same certificate to run in the same processes Never put your private key in the source code!

34. See Code Detect Non-Playstore Installation

35. Other Tamper Detection • Is the application in debug mode? • context.getApplicationInfo().flags & ApplicationInfo.FLAG_DEBUGGABLE) != 0 • Is the app running on the emulator? • is Emulator = Build.FINGERPRINT.contains("generic") or • is Emulator = "goldfish".equals(Build.HARDWARE)

36. Other Resources • Android Developers blog on LVL: Old but interestinghttp://android-developers.blogspot.com/2010/09/securing-android-lvl-applications.html • Android Licensing tutorial: • http://stackoverflow.com/questions/18324963/are-there-any-good-android-licensing-tutorials

37. Decompiling

38. Image source: http://developer.android.com/tools/building/index.html

39. Inside the .dex binary Inside the .apk Image source http://developer.android.com/tools/building/index.html *Are are curious about why Android uses .dex files and the Davlik virtual machine? Check out http://davidehringer.com/software/android/The_Dalvik_Virtual_Machine.pdf How about further decompiling dex files? Check out https://code.google.com/p/smali/wiki/

40. For Fun:MasterKey Exploit • Want to see if you are vulnerable? Check out the Bluebox Security Scanner on the app store. • Additional details on exactly how the masterkey vulnerability works • http://vrt-blog.snort.org/2013/08/bytecode-covering-android.html

41. Decompiling Demo

42. What is ProgUArd? • Shrinking • Obfuscation • Prevarifacation *Fun random fact: you can run Scala on android by using progaurd to remove the unneeded library classes http://www.gamlor.info/wordpress/2011/10/running-scala-on-android/

43. Enabling Progaurd in Eclipse • In project.properties • Uncomment • #proguard.config=${sdk.dir}/tools/proguard/proguard-android.txt:proguard-project.txt *For versions past 17 the documentation on android developers is slightly misleading You can ignore the warning when it comes to progaurd the default progaurd config file will be proguard-project.txt instead of proguard.cfg

44. Enabling Proguard in Android Studio • In build.gradel • android { •     buildTypes { •         release { •             runProguard true •             proguardFile getDefaultProguardFile('proguard-android.txt') •         } •     } For more detailed descriptions see http://tools.android.com/tech-docs/new-build-system/user-guide#TOC-Running-ProGuard and http://stackoverflow.com/questions/20885725/how-to-use-the-proguard-in-android-studio

45. Troubleshooting Proguard • What if I get a file not found error after running Proguard? • add –keep public class <MyClass> to your progaurd config file. • How do a read stacktraces from my production app? • Use the retrace tool • retrace.sh mapping.txt[<stacktrace_file] • * Remember to keep the mapping.txt file for each build *It is possible to reuse mapping files with -applymappingfilename but this has pros and cons see http://proguard.sourceforge.net/index.html#

46. Things Proguard Does not do • Strings Encryption • Class Encryption • Hide Android API calls • Tamper Detection • Dexguard is a paid product by the makers of proguard that can help with some of these, but it can be pricy. • http://www.saikoa.com/dexguard • DashO is also an option

47. Extra Stuff

48. Check out Current known Vulnerabilities http://www.cvedetails.com/vulnerability-list/vendor_id-1224/product_id-19997/Google-Android.html

49. Additional Resources • Android Security Cookbook • There is a 50% off coupon at http://www.packtpub.com/article/knowing-sql-injection-attacks-securing-android-applications • Learning Pentesting for Android Devices • Android Application Security Essentials • Android Explorations blog by Nikolay Elenkov • http://nelenkov.blogspot.ie/ • Open Web Application Security Project • https://www.owasp.org/ • SELinux • https://www.ibm.com/developerworks/library/l-selinux/

50. Thank you. Questions?