Lecture 9 PSiOS: Bring Your Own Privacy & Security to iOS Devices Tim Werthmann, Ralf Hund, Lucas Davi, Ahmad-Reza Sadeghi and Thorsten Holz Operating Systems Practical December 3, 2014 OSP Lecture 9, PSiOS 1/35
Introduction iOS Internals PSiOS Design Implementation Evaluation Keywords OSP Lecture 9, PSiOS 2/35
Outline Introduction iOS Internals PSiOS Design Implementation Evaluation Keywords OSP Lecture 9, PSiOS 3/35
General Idea ◮ large number of mobile devices and mobile apps ◮ privacy is important, attacks are frequent ◮ need for privacy framework for iOS ◮ PSiOS: detects and prevents alterations of control-flow graph ◮ Privacy and Security for iOS ◮ define profiles and enabled fine-grained policy ◮ use static analysis to generate control-flow graph ◮ hook into the Objective-C runtime of iOS OSP Lecture 9, PSiOS 4/35
Smartphone and iOS Market ◮ large number of applications ◮ app stores (Google Play, Apple AppStore) ◮ Android (open) and iOS (closed) OSP Lecture 9, PSiOS 5/35
iOS Security ◮ assign a generic profile to every third party application ◮ guidelines for developpers ◮ vetting process in the AppStore ◮ several apps have been able to abuse privileges OSP Lecture 9, PSiOS 6/35
Outline Introduction iOS Internals PSiOS Design Implementation Evaluation Keywords OSP Lecture 9, PSiOS 7/35
iOS Architecture OSP Lecture 9, PSiOS 8/35
Application Sandboxing ◮ only happening at kernel-level, not within the Objective-C runtime ◮ course-grained sandboxing, cannot enforce fine-grained control within the Objective-C runtime ◮ iOS provides entitlements for additional rules; but they are defined by the developer and can not be subsequently changed by the user OSP Lecture 9, PSiOS 9/35
Objective-C Runtime ◮ applications written in Objective-C ◮ main system libraries written in Objective-C ◮ decisions deferred from compile-time to runtime ◮ iOS objective C libraries included in frameworks: a directory with a shared library and its resources OSP Lecture 9, PSiOS 10/35
Public and Private Frameworks ◮ public frameworks are accessible to apps ◮ private frameworks are only accessible to system applications ◮ “interesting” functionality is located inside private frameworks OSP Lecture 9, PSiOS 11/35
The Problem ◮ generic application sandboxing profile assigned to every third-party application ◮ enforced by the kernel ◮ attacks have been reported that abuse privileges ◮ no enforcing within the Objective-C runtime OSP Lecture 9, PSiOS 12/35
Outline Introduction iOS Internals PSiOS Design Implementation Evaluation Keywords OSP Lecture 9, PSiOS 13/35
High-Level Idea OSP Lecture 9, PSiOS 14/35
High-Level Idea ◮ policy enforcement component checks profile rules defined by the user ◮ hooks into all Objective-C runtime calls ◮ enforces Control Flow Integrity (CFI); validates control-flow graph and prevents control-flow attacks OSP Lecture 9, PSiOS 15/35
Static Analysis ◮ iOS apps are encrypted by default ◮ uses process dumping to create application memory snapshot ◮ sues improved static Objective-C analyzer to extract the control-flow graph and Objective-C information OSP Lecture 9, PSiOS 16/35
Load-Time Binary Rewriting ◮ binary rewriting performed after loader (to preserve application signature) ◮ patches all indirect branches with a control flow check ◮ inserts checkpoints into calls to Objective-C runtime ◮ whenever a checkpoint is reached, the CFG is checked/validated OSP Lecture 9, PSiOS 17/35
Architecture OSP Lecture 9, PSiOS 18/35
Runtime Enforcing ◮ employed by the policy enforcement component ◮ three types of enforcing: Log , Exit and Replace ◮ Replace replaces return information with shadow data to prohibit access to sensitive information ◮ it is possible to create a central instance of to deploy policies (to centralize them in a given organization) OSP Lecture 9, PSiOS 19/35
Sandboxing Profile Format 1 < rule type="objc" class="NSUserDefaults" 2 selector="valueForKey:" mode="exit" > < argnumber ="1" type="string" operator="=" 3 value="SBFormattedPhoneNumber" / > 4 5 < /rule > OSP Lecture 9, PSiOS 20/35
Outline Introduction iOS Internals PSiOS Design Implementation Evaluation Keywords OSP Lecture 9, PSiOS 21/35
Tools of the Trade ◮ support for iOS 4.3.2, 4.3.3, 5.0.1, 5.1.1 ◮ Python module in IDA Pro 6.x for the static Objective-C analyzer ◮ MoCFI framework for CFI ◮ extended MoCFI to introduce the policy enformence component OSP Lecture 9, PSiOS 22/35
Deploying PSiOS ◮ as a shared library ◮ shared library is injected into every application, through setting a variable similar to LD_PRELOAD on Linux ◮ requires jailbreak OSP Lecture 9, PSiOS 23/35
Static Objective-C Analyzer ◮ parses Mach-O file and locate code and data sections ◮ identifies Objective-C classes and selectors ◮ record call to the objc_msgSend dispatcher function ◮ resolve calls to public frameworks by inspecting the symbol section ( __lazy_symbol ) OSP Lecture 9, PSiOS 24/35
Objective-C Runtime Analyzer ◮ starts operating after application is loaded ◮ retrieve runtime address of selectors ◮ retrieve runtime adress of classes ◮ uses sections in the executable image in memory ( __objc_selrefs and __objc_classrefs ) OSP Lecture 9, PSiOS 25/35
Policy Enforcement ◮ enforces control on each Objective-C message ◮ use analyzers to extract the runtime address ◮ parse the sandboxing profile ◮ MoCFI validates control-flow integrity ◮ applies policy, if policy is defined for class/selector ◮ for the Replace rule, a new implementation of the method is used (already prepared, returns empty data) OSP Lecture 9, PSiOS 26/35
Outline Introduction iOS Internals PSiOS Design Implementation Evaluation Keywords OSP Lecture 9, PSiOS 27/35
SpyPhone ◮ open source app, capable of retrieving infomrmation ◮ may retrieve e-mail information, phone data, location, address book entries ◮ successfully applied rules to prevent SpyPhone from accessing address book entries OSP Lecture 9, PSiOS 28/35
PSiOS to iOS Apps ◮ tested on Facebook, WhatsApp, Flashlight, Instagram etc. ◮ successfully used PSiOS to prevent access to the address book, personal photos, short UUID OSP Lecture 9, PSiOS 29/35
Performance Overhead using Gensystek App OSP Lecture 9, PSiOS 30/35
Runtime Performance Using Different Apps OSP Lecture 9, PSiOS 31/35
Jailbreaking ◮ PSiOS is injected as a shared library ◮ this requires a jailbroken devices ◮ this is only required when setting up the environment, by setting a library similar to LD_PRELOAD on Linux ◮ if PSiOS were to be used by Apple, it could be implemented as a static rewriter to be used before the app is signed by Apple OSP Lecture 9, PSiOS 32/35
Conclusion ◮ novel policy enforcement framework: PSiOS ◮ provides fine-grained application sandboxing ◮ effective in preventing privay breaches (SpyPhone and popular iOS apps) ◮ reasonable overhead ◮ future work in providing PSiOS as a static rewriter OSP Lecture 9, PSiOS 33/35
Outline Introduction iOS Internals PSiOS Design Implementation Evaluation Keywords OSP Lecture 9, PSiOS 34/35
Keywords ◮ mobile apps ◮ control flow graph ◮ iOS ◮ PSiOS ◮ sandboxing ◮ policy enforcement ◮ Objective C ◮ CFI ◮ fine-grained sandboxing ◮ static analysis ◮ static analysis ◮ jailbreak OSP Lecture 9, PSiOS 35/35
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