[NT] Trillian Pro Rendezvous XMPP HTML Decoding Heap Corruption

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Trillian Pro Rendezvous XMPP HTML Decoding Heap Corruption
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SUMMARY

A vulnerability allows remote attackers to execute arbitrary code on
vulnerable installations of Cerulean Studios Trillian Pro. Authentication
is not required to exploit this vulnerability.

DETAILS

Vulnerable Systems:
* Trillian Pro version 3.1 build 121

The specific flaw exists in the Rendezvous / XMPP (Extensible Messaging
and Presence Protocol) messaging subsystem. Trillian locates nearby users
through the '_presence' mDNS (multicast DNS) service on UDP port 5353.
Once a user is registered through mDNS, messaging is accomplished via XMPP
over TCP port 5298. Within plugins\rendezvous.dll the follow logic is
applied to received messages:

4900C470 str_len:
4900C470 mov cl, [eax] ; *eax = message+1
4900C472 inc eax
4900C473 test cl, cl
4900C475 jnz short str_len

4900C477 sub eax, edx
4900C479 add eax, 128 ; strlen(message+1) + 128
4900C47E push eax
4900C47F call _malloc

The string length of the the supplied message is calculated and a heap
buffer in the amount of length + 128 is allocated to store a copy of the
message which is then passed through expatxml.xmlComposeString(), a
function called with the following prototype:

plugin_send(MYGUID, "xmlComposeString", struct xml_string_t *);

struct xml_string_t {
unsigned int struct_size;
char *string_buffer;
struct xml_tree_t *xml_tree;
};

The xmlComposeString() routine calls through to expatxml.19002420() which,
among other things, HTML encodes the characters &, > and < as &, > and <
respectively. This behavior can be seen in the following disassembly
snippet:

19002492 push 0
19002494 push 0
19002496 push offset str_Amp ; "&"
1900249B push offset ampersand ; "&"
190024A0 push eax
190024A1 call sub_190023A0

190024A6 push 0
190024A8 push 0
190024AA push offset str_Lt ; "<"
190024AF push offset less_than ; "<"
190024B4 push eax
190024B5 call sub_190023A0

190024BA push
190024BC push
190024BE push offset str_Gt ; ">"
190024C3 push offset greater_than ; ">"
190024C8 push eax
190024C9 call sub_190023A0

As the originally calculated string length does not account for this
string expansion, the following subsequent in-line memory copy operation
within rendezvous.dll can trigger an exploitable memory corruption:

4900C4EC mov ecx, eax
4900C4EE shr ecx, 2
4900C4F1 rep movsd
4900C4F3 mov ecx, eax
4900C4F5 and ecx, 3
4900C4F8 rep movsb

Note that binary data can be transmitted across the XMPP protocol via
UTF-8 encoding.

Vendor Response:
Cerulean Studios has issued an update to correct this vulnerability. More
details can be found at: <http://blog.ceruleanstudios.com/>

http://blog.ceruleanstudios.com/

Disclosure Timeline:
2007.02.15 - Vulnerability reported to vendor
2007.05.02 - Digital Vaccine released to TippingPoint customers
2007.05.02 - Coordinated public release of advisory

CVE Information:
<http://www.cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2007-2418>
CVE-2007-2418

ADDITIONAL INFORMATION

The information has been provided by <mailto:Pedram Amini, TippingPoint
Security Research Team> Pedram Amini, TippingPoint Security Research Team.
The original article can be found at:
<http://dvlabs.tippingpoint.com/advisory/TPTI-07-06>

http://dvlabs.tippingpoint.com/advisory/TPTI-07-06

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