TPTI-07-06: Trillian Pro Rendezvous XMPP HTML Decoding Heap Corruption

[TSRT@xxxxxxxx]

TPTI-07-06: Trillian Pro Rendezvous XMPP HTML Decoding Heap Corruption
http://dvlabs.tippingpoint.com/advisory/TPTI-07-06
May  2, 2007

-- CVE ID:
CVE-2007-2418

-- Affected Vendor:
Cerulean Studios

-- Affected Products:
Trillian Pro 3.1 build 121 and below

-- TippingPoint(TM) IPS Customer Protection:
TippingPoint IPS customers have been protected against this
vulnerability since May  2, 2007 by Digital Vaccine protection
filter ID 5328. For further product information on the TippingPoint IPS:

    http://www.tippingpoint.com 

-- Vulnerability Details:
This vulnerability allows remote attackers to execute arbitrary code on
vulnerable installations of Cerulean Studios Trillian Pro.
Authentication is not required to exploit this vulnerability.

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/

-- 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

-- Credit:
This vulnerability was discovered by Pedram Amini, TippingPoint Security
Research Team.