Source: https://bugs.chromium.org/p/project-zero/issues/detail?id=1309

There is a security issue in Microsoft Edge related to how HTML documents are loaded. If Edge displays a HTML document from a slow HTTP server, it is possible that a part of the document is going to be rendered before the server has finished sending the document. It is also possible that some JavaScript code is going to trigger.

By making DOM modifications before the document had a chance of fully loading, followed by another set of DOM modifications afer the page has been loaded, it is possible to trigger memory corruption that could possibly lead to an exploitable condition.

A debug log is included below. Note that the crash RIP directly preceeds a (CFG-protected) indirect call, which demonstrates the exploitability of the issue.

Since a custom HTTP server is needed to demonstrate the issue, I'm attaching all of the required code. Simply run server.py and point Edge to http://127.0.0.1:8000/

Note: this has been tested on Microsoft Edge 38.14393.1066.0 (Microsoft EdgeHTML 14.14393)


Debug log:

=========================================

(a68.9c0): Access violation - code c0000005 (first chance)
First chance exceptions are reported before any exception handling.
This exception may be expected and handled.
edgehtml!`TextInput::TextInputLogging::Instance'::`2'::`dynamic atexit destructor for 'wrapper''+0x1389aa:
00007ffa`9d5f15ea 488b01          mov     rax,qword ptr [rcx] ds:00000000`abcdbbbb=????????????????

0:013> k
 # Child-SP          RetAddr           Call Site
00 000000eb`c42f8da0 00007ffa`9d8b243d edgehtml!`TextInput::TextInputLogging::Instance'::`2'::`dynamic atexit destructor for 'wrapper''+0x1389aa
01 000000eb`c42f8dd0 00007ffa`9d8b28e2 edgehtml!Collections::SGrowingArray<TSmartPointer<Tree::ANode,CStrongReferenceTraits> >::DeleteAt+0x89
02 000000eb`c42f8e00 00007ffa`9d8b0cd7 edgehtml!Undo::UndoNodeList::RemoveNodesCompletelyContained+0x5e
03 000000eb`c42f8e30 00007ffa`9d8ad79b edgehtml!Undo::WrapUnwrapNodeUndoUnit::RemoveNodesAtOldPosition+0x33
04 000000eb`c42f8e70 00007ffa`9d5b303d edgehtml!Undo::MoveForestUndoUnit::HandleWrapUnwrap+0x6b
05 000000eb`c42f8f10 00007ffa`9d8ac629 edgehtml!`TextInput::TextInputLogging::Instance'::`2'::`dynamic atexit destructor for 'wrapper''+0xfa3fd
06 000000eb`c42f8f60 00007ffa`9d5b3085 edgehtml!Undo::ParentUndoUnit::ApplyScriptedOperationToChildren+0xb5
07 000000eb`c42f8ff0 00007ffa`9d11035c edgehtml!`TextInput::TextInputLogging::Instance'::`2'::`dynamic atexit destructor for 'wrapper''+0xfa445
08 000000eb`c42f9040 00007ffa`9d110125 edgehtml!Undo::UndoManager::ApplyScriptedOperationsToUserUnits+0x11c
09 000000eb`c42f9130 00007ffa`9d1d6f0d edgehtml!Undo::UndoManager::SubmitUndoUnit+0x125
0a 000000eb`c42f9170 00007ffa`9dc9c9ae edgehtml!CSelectionManager::CreateAndSubmitSelectionUndoUnit+0x141
0b 000000eb`c42f9200 00007ffa`9dc90b70 edgehtml!CRemoveFormatBaseCommand::PrivateExec+0xae
0c 000000eb`c42f92c0 00007ffa`9dc9057a edgehtml!CCommand::Exec+0xe8
0d 000000eb`c42f9350 00007ffa`9d55e481 edgehtml!CMshtmlEd::Exec+0x17a
0e 000000eb`c42f93b0 00007ffa`9d39cc34 edgehtml!`TextInput::TextInputLogging::Instance'::`2'::`dynamic atexit destructor for 'wrapper''+0xa5841
0f 000000eb`c42f9470 00007ffa`9d21d6a1 edgehtml!CDoc::ExecHelper+0x5d18
10 000000eb`c42fb020 00007ffa`9d1dbb57 edgehtml!CDocument::Exec+0x41
11 000000eb`c42fb070 00007ffa`9d1dba25 edgehtml!CBase::execCommand+0xc7
12 000000eb`c42fb0f0 00007ffa`9d1db8ac edgehtml!CDocument::execCommand+0x105
13 000000eb`c42fb2e0 00007ffa`9d498155 edgehtml!CFastDOM::CDocument::Trampoline_execCommand+0x124
14 000000eb`c42fb3f0 00007ffa`9c930e37 edgehtml!CFastDOM::CDocument::Profiler_execCommand+0x25
15 000000eb`c42fb420 00007ffa`9c9e9073 chakra!Js::JavascriptExternalFunction::ExternalFunctionThunk+0x177
16 000000eb`c42fb500 00007ffa`9c9596cd chakra!amd64_CallFunction+0x93
17 000000eb`c42fb560 00007ffa`9c95cec7 chakra!Js::InterpreterStackFrame::OP_CallCommon<Js::OpLayoutDynamicProfile<Js::OpLayoutT_CallIWithICIndex<Js::LayoutSizePolicy<0> > > >+0x15d
18 000000eb`c42fb600 00007ffa`9c960f52 chakra!Js::InterpreterStackFrame::OP_ProfiledCallIWithICIndex<Js::OpLayoutT_CallIWithICIndex<Js::LayoutSizePolicy<0> > >+0xa7
19 000000eb`c42fb680 00007ffa`9c95f1b2 chakra!Js::InterpreterStackFrame::ProcessProfiled+0x132
1a 000000eb`c42fb710 00007ffa`9c963280 chakra!Js::InterpreterStackFrame::Process+0x142
1b 000000eb`c42fb770 00007ffa`9c9649c5 chakra!Js::InterpreterStackFrame::InterpreterHelper+0x4a0
1c 000000eb`c42fbad0 00000284`bf4b0fa2 chakra!Js::InterpreterStackFrame::InterpreterThunk+0x55
1d 000000eb`c42fbb20 00007ffa`9c9e9073 0x00000284`bf4b0fa2
1e 000000eb`c42fbb50 00007ffa`9c9580c3 chakra!amd64_CallFunction+0x93
1f 000000eb`c42fbba0 00007ffa`9c95abc0 chakra!Js::JavascriptFunction::CallFunction<1>+0x83
20 000000eb`c42fbc00 00007ffa`9c95f65d chakra!Js::InterpreterStackFrame::OP_CallI<Js::OpLayoutDynamicProfile<Js::OpLayoutT_CallI<Js::LayoutSizePolicy<0> > > >+0x110
21 000000eb`c42fbc50 00007ffa`9c95f217 chakra!Js::InterpreterStackFrame::ProcessUnprofiled+0x32d
22 000000eb`c42fbce0 00007ffa`9c963280 chakra!Js::InterpreterStackFrame::Process+0x1a7
23 000000eb`c42fbd40 00007ffa`9c9649c5 chakra!Js::InterpreterStackFrame::InterpreterHelper+0x4a0
24 000000eb`c42fc090 00000284`bf4b0faa chakra!Js::InterpreterStackFrame::InterpreterThunk+0x55
25 000000eb`c42fc0e0 00007ffa`9c9e9073 0x00000284`bf4b0faa
26 000000eb`c42fc110 00007ffa`9c9580c3 chakra!amd64_CallFunction+0x93
27 000000eb`c42fc160 00007ffa`9c98ce3c chakra!Js::JavascriptFunction::CallFunction<1>+0x83
28 000000eb`c42fc1c0 00007ffa`9c98c406 chakra!Js::JavascriptFunction::CallRootFunctionInternal+0x104
29 000000eb`c42fc2b0 00007ffa`9c9ce4d9 chakra!Js::JavascriptFunction::CallRootFunction+0x4a
2a 000000eb`c42fc320 00007ffa`9c9928a1 chakra!ScriptSite::CallRootFunction+0xb5
2b 000000eb`c42fc3c0 00007ffa`9c98e45c chakra!ScriptSite::Execute+0x131
2c 000000eb`c42fc450 00007ffa`9d333b2d chakra!ScriptEngineBase::Execute+0xcc
2d 000000eb`c42fc4f0 00007ffa`9d333a78 edgehtml!CJScript9Holder::ExecuteCallbackDirect+0x3d
2e 000000eb`c42fc540 00007ffa`9d35ac27 edgehtml!CJScript9Holder::ExecuteCallback+0x18
2f 000000eb`c42fc580 00007ffa`9d35aa17 edgehtml!CListenerDispatch::InvokeVar+0x1fb
30 000000eb`c42fc700 00007ffa`9d33247a edgehtml!CListenerDispatch::Invoke+0xdb
31 000000eb`c42fc780 00007ffa`9d415a62 edgehtml!CEventMgr::_InvokeListeners+0x2ca
32 000000eb`c42fc8e0 00007ffa`9d290715 edgehtml!CEventMgr::_InvokeListenersOnWindow+0x66
33 000000eb`c42fc910 00007ffa`9d2901a3 edgehtml!CEventMgr::Dispatch+0x405
34 000000eb`c42fcbe0 00007ffa`9d37434a edgehtml!CEventMgr::DispatchEvent+0x73
35 000000eb`c42fcc30 00007ffa`9d3ac5a2 edgehtml!COmWindowProxy::Fire_onload+0x14e
36 000000eb`c42fcd40 00007ffa`9d3ab23e edgehtml!CMarkup::OnLoadStatusDone+0x376
37 000000eb`c42fce00 00007ffa`9d3aa72f edgehtml!CMarkup::OnLoadStatus+0x112
38 000000eb`c42fce30 00007ffa`9d328d93 edgehtml!CProgSink::DoUpdate+0x3af
39 000000eb`c42fd2c0 00007ffa`9d32a550 edgehtml!GlobalWndOnMethodCall+0x273
3a 000000eb`c42fd3c0 00007ffa`b7a31c24 edgehtml!GlobalWndProc+0x130
3b 000000eb`c42fd480 00007ffa`b7a3156c user32!UserCallWinProcCheckWow+0x274
3c 000000eb`c42fd5e0 00007ffa`9347d421 user32!DispatchMessageWorker+0x1ac
3d 000000eb`c42fd660 00007ffa`9347c9e1 EdgeContent!CBrowserTab::_TabWindowThreadProc+0x4a1
3e 000000eb`c42ff8b0 00007ffa`ad7e9586 EdgeContent!LCIETab_ThreadProc+0x2c1
3f 000000eb`c42ff9d0 00007ffa`b7978364 iertutil!_IsoThreadProc_WrapperToReleaseScope+0x16
40 000000eb`c42ffa00 00007ffa`ba0a70d1 KERNEL32!BaseThreadInitThunk+0x14
41 000000eb`c42ffa30 00000000`00000000 ntdll!RtlUserThreadStart+0x21

0:013> r
rax=00000284bc287fd8 rbx=00000284bc287f90 rcx=00000000abcdbbbb
rdx=0000000000000000 rsi=0000000000000017 rdi=0000000000000000
rip=00007ffa9d5f15ea rsp=000000ebc42f8da0 rbp=000000ebc42f8fb0
 r8=0000000000000017  r9=000000ebc42f8e78 r10=00000fff53a47750
r11=0000000000010000 r12=0000027cb4fbcd10 r13=0000027cb4f95a78
r14=000000ebc42f8e70 r15=0000000000000000
iopl=0         nv up ei pl nz na po nc
cs=0033  ss=002b  ds=002b  es=002b  fs=0053  gs=002b             efl=00010206
edgehtml!`TextInput::TextInputLogging::Instance'::`2'::`dynamic atexit destructor for 'wrapper''+0x1389aa:
00007ffa`9d5f15ea 488b01          mov     rax,qword ptr [rcx] ds:00000000`abcdbbbb=????????????????

0:013> u 00007ffa`9d5f15ea
edgehtml!`TextInput::TextInputLogging::Instance'::`2'::`dynamic atexit destructor for 'wrapper''+0x1389aa:
00007ffa`9d5f15ea 488b01          mov     rax,qword ptr [rcx]
00007ffa`9d5f15ed 488b80d0050000  mov     rax,qword ptr [rax+5D0h]
00007ffa`9d5f15f4 ff15c654ab00    call    qword ptr [edgehtml!_guard_dispatch_icall_fptr (00007ffa`9e0a6ac0)]

=========================================


Proof of Concept:
https://gitlab.com/exploit-database/exploitdb-bin-sploits/-/raw/main/bin-sploits/42758.zip