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Message-ID: <037901c474b6$5a2328a0$0100a8c0@grotedoos>
Date: Wed, 28 Jul 2004 17:19:57 +0200
From: "Berend-Jan Wever" <skylined@...p.tudelft.nl>
To: <vulnwatch@...nwatch.org>, <full-disclosure@...ts.netsys.com>,
<bugtraq@...urityfocus.com>
Subject: Re: Internet Explorer Remote Null Pointer Crash(mshtml.dll)
Here's a detailed description of what's going wrong with the <a href=::%7b> right click bug.
(yeah, my reply is a bit late but I was busy and went on a holliday)
Right click on a link with href="file://::XXXX" and IE will try to download
it, fail and try to report an error. While creating this errormessage
FormatMessageW calls RtlFormatMessage with parts of our url in the
formatstring.
- RtlFormatMessage's arguments include a pointer to the formatstring and a
pointer to a pointer to a pointer to an Array of arguments (Array1). All
pointers, the formatstring and Array1 are on the stack.
- Array1 should contain the normal printf-type arguments (except the
formatstring ofcourse) but since none are expected to be there, the pointers
to Array1 exist but Array1 itself is totally empty (doesn't exist). The
pointer points to the end of a stack frame.
- The formatstring for RtlFormatMessage looks like this:
"%index!conversion!", eg. "%1!x!" will display Array1[0] as heX, "%2!s!"
will display Array1[1] as string.
- The actual conversion is done with _snwprintf. RtlFormatMessage passes the
destination string, the length, the formatstring, and Array1[index] as first
argument to convert. We control the formatstring and Array1[index]: %10!x%x!
will give _snwprintf %x%x as formatstring and Array1[9] as first argument.
- The href gets converted to "[file] from [server]" (XXXX from ::), which is
used as formatstring in RtlFormatMessage.
- The total href can not be more then 97 bytes or _snwprintf won't be
called.
- [file] cannot be more then 28 bytes or _snwprintf won't be called.
- "file://::XXXX/A" converts to "A from ::XXXX". Use this to bypass the
restriction on the [file]-length.
- Each conversion specifier passed to RtlFormatMessage (%index!conversion!)
cannot be more then 34 bytes or snwprintf won't be called.
- RtlFormatMessage limits to total length of the message to 10000 bytes,
each call to _snwprintf gets a proper max length accordingly.
Here's a little stack layout, I hope it doesn't get to mangled:
Address Stack Procedure / arguments Called from
Frame
xxxxEB3C 77F8F40C ntdll._snwprintf ntdll.77F8F407
xxxxEED8
xxxxEB40 yyyyyyyy destination = yyyyyyyy
xxxxEB44 00010000 count = 10000 (10000-allready printed chars)
xxxxEB48 xxxxEE84 format = "%x" (conversion)
xxxxEB4C xxxxxxxx = 1 Array1[index]
xxxxEB50 00000000 = 0
xxxxEB54 00000000 = 0
xxxxEB58 00000500 = 0x500
xxxxEB5C 00000000 = 0
xxxxEB60 00000000 = 0
xxxxEB64 xxxxFE6C = &Array1[1]
xxxxEEDC 7C57F221 ntdll.RtlFormatMessage
KERNEL32.7C57F21B xxxxEF74
xxxxEEE0 04246F30 Source = UNICODE "A from ::%1!x!"
xxxxEEE4 00000000
xxxxEEE8 00000000
xxxxEEEC 00000000
xxxxEEF0 00000000
xxxxEEF4 xxxxFE24 Arguments = xxxxFE24 [&&&Array of arguments]
xxxxEEF8 yyyy0000 Destination = freshly allocated heap.
xxxxEEFC 00010000 Length = 10000 (updated by RtlFormatMessage and
passed to _snwprintf)
xxxxEF64 xxxxFFDC [Pointer to next SEH record]
xxxxEF68 xxxxxxxx [SE handler]
xxxxEF78 7C57F2CB KERNEL32.7C57F102
KERNEL32.7C57F2C6 xxxxEF74
xxxxEFA0 70A9D0CD KERNEL32.FormatMessageW SHLWAPI.70A9D0C7
xxxxEF9C
xxxxEFA4 00000500 Flags = ALLOCATE_BUFFER|FROM_STRIN
xxxxEFA8 04246F30 pSource = 04246F30
xxxxEFAC 00000000 MessageId = 0
xxxxEFB0 00000000 LanguageId = 0 (LANG_NEUTRAL)
xxxxEFB4 xxxxFE28 Buffer = xxxxFE28
xxxxEFB8 00000000 BufSize = 0
xxxxEFBC xxxxFE24 Arguments = xxxxFE24 [&&&Array of arguments]
xxxxF3F8 7174B9DD SHLWAPI.#68 SHDOCVW.7174B9D7
xxxxF3F4
xxxxFC38 UNICODE "::%1!x!/A"
xxxxFE24 xxxxFE44 [&&Array of arguments]
xxxxFE30 7175E158 SHDOCVW.7174B97C SHDOCVW.7175E153
xxxxFE2C
xxxxFE44 xxxxFE6C [&Array of arguments]
xxxxFE48 717610C6 SHDOCVW.7175E122 SHDOCVW.717610C1
xxxxFE44
xxxxFE6C xxxxFEA4 [arg 1 -> arg 15]
xxxxFE70 7176111D SHDOCVW.7176103E SHDOCVW.7176111D
xxxxFE74 00199020
xxxxFE78 001D4358
xxxxFE94 001D5F74
xxxxFEA4 xxxxFEEC [arg 15 -> arg 33 ]
xxxxFEA8 71761331 RETURN to SHDOCVW.71761331 from SHDOCVW.717610EC
xxxxFEAC 00199020
xxxxFEB0 001D4358
xxxxFED0 001D5F74
xxxxFEE4 001D5F50
xxxxFEE8 00199020
xxxxFEEC xxxxFF50 [ arg 33 -> ... ]
xxxxFEF0 717604AB RETURN to SHDOCVW.717604AB from SHDOCVW.717612E2
xxxxFEF4 00199C80 (arg 35) UNICODE "file://:|%1!x!/A"
xxxxFE70 7176111D SHDOCVW.7176103E SHDOCVW.71761118
xxxxFE6C
xxxxFEA8 71761331 SHDOCVW.717610EC SHDOCVW.7176132C
xxxxFEA4
xxxxFEF0 717604AB SHDOCVW.717612E2 SHDOCVW.717604A6
xxxxFEEC
xxxxFF50 040BFFB4 [ ... -> ... ]
xxxxFF54 70AAC487 Includes SHDOCVW.717604AB SHLWAPI.70AAC484
xxxxFF50
xxxxFFB8 7C57438B Includes SHLWAPI.70AAC487
KERNEL32.7C574388 xxxxFFB4
xxxxFFDC FFFFFFFF [Pointer to next SEH record]
xxxxFFE0 xxxxxxxx [SE handler]
Is this exploitable ? Probably not...
1. I can't reach the SEH. RtlFormatMessage doesn't allow enough room in the
formatstring to have _snwprintf do stackpopping and overwrite it.
2. I can't overwrite anything with a proper value: I can print 0x10000 bytes
max, so I can only overwrite with values 00000000-00010000. %hn is nice, but
then I'd have to have two pointers that point to the high and low word of
something usefull. And I can't use integer overflow with %hn to write a big value followed by a small value.
Cheers,
SkyLined
----- Original Message -----
From: "Rafel Ivgi, The-Insider" <theinsider@....net.il>
To: "vulnwatch" <vulnwatch@...nwatch.org>
Sent: Monday, June 14, 2004 23:20
Subject: [Full-Disclosure] Internet Explorer Remote Null Pointer Crash(mshtml.dll)
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>
> Application: Internet Explorer
> Vendors: http://www.microsoft.com
> Versions: 6.0.2800.1106.xpclnt_qfe.021108-2107
> Patched With: SP1;Q832894;Q330994;Q837009;Q831167;
> ModName: mshtml.dll
> ModVer: 6.0.2734.1600
> Platforms: Windows
> Bug: Remote/Local Null Pointer Crash
> Exploitation: Remote with browser
> Date: 14 Jun 2004
> Author: Rafel Ivgi, The-Insider
> e-mail: the_insider@...l.com
> web: http://theinsider.deep-ice.com
>
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>
> 1) Introduction
> 2) Bugs
> 3) The Code
>
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>
> ===============
> 1) Introduction
> ===============
>
> Internet Explorer is currently the most common internet browser in the
> world.
> It comes by default with every windows operating system. Therefore any
> vulnerability
> concerning it is an highly important issue.
>
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>
> ======
> 2) Bug
> ======
>
> Upon clicking "Save As" on a link with double colon --> "::"
> and
> a left curly bracket --> "{"
> then
> Internet Explorer Will Crash.
>
> AppName: iexplore.exe AppVer: 6.0.2600.0 ModName: ntdll.dll
> ModVer: 5.1.2600.114 Offset: 00056074
>
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>
> ===========
> 3) The Code
> ===========
>
> Paste into an htm/html file:
> <center><a href=::%7b>Right Click aOn Me And Click "Save Target As"</a>
>
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>
> ---
> Rafel Ivgi, The-Insider
> http://theinsider.deep-ice.com
>
> "Scripts and Codes will make me D.O.S , but they will never HACK me."
>
> _______________________________________________
> Full-Disclosure - We believe in it.
> Charter: http://lists.netsys.com/full-disclosure-charter.html
_______________________________________________
Full-Disclosure - We believe in it.
Charter: http://lists.netsys.com/full-disclosure-charter.html
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