Blue Frost Security GmbH https://www.bluefrostsecurity.de/ research(at)bluefrostsecurity.de BFS-SA-2015-001 12-August-2015 ________________________________________________________________________________ Vendor: Microsoft, http://www.microsoft.com Affected Products: Internet Explorer Affected Version: IE 8-11 Vulnerability: CTreeNode::GetCascadedLang Use-After-Free Vulnerability CVE ID: CVE-2015-2444 ________________________________________________________________________________ I. 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 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::GetCascadedLang function. The following analysis was performed on Internet Explorer 11 on Windows 8.1 (x64). The following HTML page demonstrates the problem: With page heap enabled, visiting that page results in the following crash: (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=???????? 0:005> 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] 0:005> !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 0:005> 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 ________________________________________________________________________________ III. Mitigation The issue was fixed in MS15-079 which should be installed to resolve the issue. ________________________________________________________________________________ IV. Disclosure Timeline - 2015-05-11 Vulnerability reported to secure@microsoft.com - 2015-05-11 Acknowledgement of received report - 2015-05-14 Microsoft confirms that they successfully reproduced the issue - 2015-06-03 Requested a status update - 2015-06-03 Microsoft confirms that they are currently working on a fix and they want to know if hitting the August patch day would be acceptable, because that would be 2 days after the 90 day disclosure timeline - 2015-07-14 Requested a status upate - 2015-07-15 Microsoft confirms to be on track for the August patch day - 2015-08-10 Requested another status update - 2015-08-11 Microsoft resolves issue in MS15-079 ________________________________________________________________________________ Credit: Bug found by Moritz Jodeit of Blue Frost Security GmbH. ________________________________________________________________________________ Unaltered electronic reproduction of this advisory is permitted. 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