An Analysis of the Mozilla Jetpack Extension Framework Rezwana Karim, Mohan Dhawan, Vinod Ganapathy Computer Science, Rutgers University Chung-cheih Shan Indiana University 6/1/2012 ECOOP’12

Browser Extensions Enhance browser functionality Customize to meet user need Unrestricted access to privileged resource Rezwana Karim2

Problems in legacy extensions 3Rezwana Karim Insecure Programming Practice  Exploitable vulnerability [Barth et al., NDSS‘10] [Bhandhakavi et al., Usenix Security‘10]

Jetpack Mozilla’s new extension development technology Extension structured as a collection of modules Recommends –Principle of Least Authority (POLA) –Privilege separation Upfront permission specification Goal : Limit ill effects of vulnerable extensions 4Rezwana Karim

Structure of Weather extension in Jetpack Rezwana Karim5 Sensitive resources Core modules File Network Main Extension modules

Modularity does not guarantee security 6 File Network Main Rezwana Karim

Analysis of Jetpack framework Goal: Verifying conformance to security principles in Jetpack modules –Focus on adherence to POLA and privilege separation Beacon: Capability flow analysis tool –36 programming bugs in real-world extensions –10 instances of POLA violation –Results acknowledged by Mozilla 7Rezwana Karim

Module Interaction 8 var file = require(“file”); file.readFile (“zipCodeFile”);... Main var fileSystemPtr = accessToFileSystem(); exports.readFile = function readFile(fileName){ //read the content of fileName... // return the content... }; File Rezwana Karim

Capabilities Rezwana Karim 9 Privilege to access sensitive resources Bookmark, cookies, file, password, network etc. Ways to acquire var fileSystemPtr = accessToFileSystem(); exports.fileSystemPtr = fileSystemPtr; File var fileSystemPtr = require(“File”).fileSystemPtr; Main

Capability leaks Inadvertent leaks of pointers to privileged resources –Direct references to privileged resources –Functions returning references to privileged resources 10Rezwana Karim var fileSystemPtr = accessToFileSystem(); exports.fileSystemPtr = fileSystemPtr; exports.getFileSystem = function(){ return fileSystemPtr; } File

Detecting capability leaks 11 File Network Main Rezwana Karim

Capability flow analysis Static analysis of JavaScript modules Information flow –Taint: capability –Source : privileged resource access –Sink: exports interface Call graph based Context and Flow insensitive –Static Single Assignment (SSA) representation gives a degree of flow-sensitivity 12Rezwana Karim

Capability flow in object hierarchy 13 a a x x y y p p z z Rezwana Karim var a = { x : object, y : { p : fileSystemPtr, z : object }

Implementation of Beacon 14 Call graph generator SSA analyzer Inference engine SSA format Imported module summaries Imported module summaries Rules for JS to Datalog translation Taint inference rules Initial facts Points-to rules Heap allocation Rezwana Karim Capability analysis report 2.8k lines of Java, Datalog Tools Used : WALA, DES

Capability flow in object hierarchy 15 a a x x y y p p z z ptsTo(v a, h a ) ptsTo(v y, h y ) ptsTo(v z, h z ) ptsTo(v p, h p ) ptsTo(v x, h x ) heapPtsTo(h y, z, h z ) heapPtsTo(h a, y, h y ) heapPtsTo(h y, p, h p ) var a ={ x : object, y:{ p: fileSystemPtr, z: object } isTainted(h p, file) isTainted(h y, file) isTainted(h a, file) Rezwana Karim store(v y, p, v p ) heapPtsTo(h a, x, h x ) [Gatekeeper, Guarnieri et al., Usenix Security’09]

Evaluation goals Evaluate Jetpack architecture, adherence to two principles –Privilege separation –Principle of least authority (POLA) Identify modules –Capability leaks –Violate privilege separation –Overprivileged; violate POLA 16Rezwana Karim

Evaluation Over 600 Jetpack modules –77 core modules –Modules from 359 Jetpack extensions –68k lines of JavaScript code Performance –On average, couple of minutes, 200 MB –tab-browser.js (~25 KB) 30mins and 243MB 17Rezwana Karim

Capability leak 36 Leaks in over 600 modules –12 in 4 core modules –24 in extension modules 18 Core ModulesCapabilityLeak MechanismEssential tabs/utilsActive tab, browser window and tab container Function returnyes window-utilsBrowser windowFunction returnyes xhrReference to the XMLHttpRequest object Property of this object no xpcomEntire XPCOM utility module Exported propertyno Rezwana Karim

Capability leaks: extension module 19Rezwana Karim 24 leaks in 359 extensions ExtensionCapabilityCount Bookmarks Deiconizer Sensitive resource service module 1 Browser Sign In Window, document 2 Customizable Shortcut Preference, DOM, window 3 Firefox Share Preference, window, database, observer database, stream, network 10 Most Recent Tab Preference, window 2 Open Web Apps Preference, window, database, observer 4 Recall Monkey IOService, favIcon 2 None of the leaks are required for functionality

Accuracy: Capability leak No False Positive May miss some leaks –Dynamic features Iterator, generator –Unsupported JS constructs for..each, yield, case statement over a variable –Unmodeled JS constructs eval, with –Latent bugs 20Rezwana Karim

Violation of privilege separation 21Rezwana Karim 26 modules in 19 extensions

Accuracy: Capability usage 53 extensions directly use sensitive resources Beacon detects 46 out of 53 Missed 7 are in event-handling code 22Rezwana Karim

Violation of POLA Beacon generates 18 warnings, 7 false positive 23 Core modulePrivilegeSeverity fileDirectory serviceModerate hidden-frameTimerNone tab-browserErrorsNone content/content-proxyChromeCritical content/loaderFileModerate content/workerChromeCritical keyboard/utilsChromeCritical clipboardErrorsNone widgetChromeCritical windowsXPCOM, apiUtilsCritical Rezwana Karim Violation instances are fixed by Mozilla

Related Work Information flow analysis of extension –SABRE [Dhawan et al., ACSAC’09] –VEX [Bhandhakavi et al., Usenix Security‘10] Static analysis of JavaScript –Gatekeeper [Guarnieri et al., Usenix Security’09] –ENCAP [Taly et al., Oakland‘11] Study of Chrome extension architecture –Chrome extension analysis [Yan et al., NDSS’12] 24Rezwana Karim

Summary Beacon, a system for capability flow analysis of JavaScript modules Analyze Jetpack extension development framework –36 capability leaks in more than 600 modules –10 overprivileged core modules –Results acknowledged by Mozilla Applicable to node.js, Harmony modules 25Rezwana Karim

Thank you 26 Rezwana Karim

Questions Rezwana Karim27

Sensitive resources usage Rezwana Karim28

Capability Usage Top 10 XPCOM interfaces 29Rezwana Karim

Suggestion Dynamic enforcement of Manifest –Prevent access of unrequested sensitive resources Deep freezing of exports object –Prevent leak through event-handlers 30Rezwana Karim

Template EntityTypeCapability fileSystemPtrObjectFile getFileSystemPtrFunctionFile Rezwana Karim31

Proof of concept example: Customize-shortcut const {Cc, Ci} = require("chrome"); let Preferences = { branches: {},... getBranch: function (name) { let branch = … return this. branches [name] = branch; },... }; exports. Preferences = Preferences ; 32

Modular approach Rezwana Karim 33 Break down extension into modules JavaScript modules –Implement a certain functionality –Self-contained –Isolated; communicate via module interfaces Limit vulnerability effect

Capability Usage Top 10 core modules 34Rezwana Karim

Datalog relations: points-to analysis 35Rezwana Karim

JavaScript statement processing 36Rezwana Karim

Inference Rules 37Rezwana Karim

Pre-processing(cont’d) Desugar JS construct –Destructuring assignment, let, const, lambda function Code simplification 38 CodeDesugared Code var {Cc,Ci} = require(“chrome”); var Cc = require(“chrome”).Cc; var Ci = require(“chrome”).Ci; CodeSimplified Code let branch = preferences-service;1”].getService(Ci.nsIPrefService).getBranch(name); let branch = MozPrefService().getBranch(name); Rezwana Karim

Capability flow in object hierarchy 39 a a x x y y p p z z ptsTo(v a, h a ) ptsTo(v y, h y ) ptsTo(v z, h z ) ptsTo(v p, h p ) ptsTo(v x, h x ) heapPtsTo(h y, z, h z ) heapPtsTo(h a, y, h y ) heapPtsTo(h y, p, h p ) var a ={ x : object, y:{ p: fileSystemPtr, z: object } isTainted(h p, file) isTainted(h y, file) isTainted(h a, file) Rezwana Karim store(v y, p, v p ) heapPtsTo(h a, x, h x )

Capability flow analysis using Datalog StatementExample CodeGenerated Facts OBJECT LITERAL a = { }ptsTo(v a, h a ) STOREv 1.f = v 2 store(v 1, f, v 2 ) 40Rezwana Karim Basic Rules heapPtsTo(H1, F, H2):-store(V 1, F, V 2 ), ptsTo(V1, H1), ptsTo(V 2, H 2 ) Taint Propagation isTainted(H1, P):-heapPtsTo(H1, F, H2 ), isTainted(H2, P) [Gatekeeper, Guarnieri et al., Usenix Security’09]

Capability flow in object hierarchy 41 a a x x y y p p z z ptsTo(v a, h a ) ptsTo(v y, h y ) ptsTo(v z, h z ) ptsTo(v p, h p ) ptsTo(v x, h x ) heapPtsTo(h y, z, h z ) heapPtsTo(h a, y, h y ) heapPtsTo(h y, p, h p ) var a ={ x : object, y:{ p: fileSystemPtr, z: object } isTainted(h p, file) isTainted(h y, file) isTainted(h a, file) Rezwana Karim store(v y, p, v p ) heapPtsTo(h a, x, h x )

JavaScript statement processing StatementExample CodeGenerated Facts OBJECT CONSTRUCTION v = new v 0 (v 1, v 2,..., v n )ptsTo(v, h fresh ) prototypeOf(h fresh, d) :- ptsTo(v0, h method ), heapPtsTo(h method, prototype, d) for z ∈ 1...n, generate actual(i, z, v z ) callRet(i, v) FUNCTION CALLv = v0(v this, v 1, v 2,..., v n ) ptsTo(v, h fresh ) for z ∈ 1...n, this, generate actual(i, z, v z ) callRet(i, v) 42Rezwana Karim