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Trillian Pro Rendezvous / XMPP HTML Decoding Heap Corruption Vulnerability

TPTI-07-06: May 2nd, 2007

CVE ID

Affected Vendors

Affected Products

TippingPoint™ IPS Customer Protection

TippingPoint IPS customers are protected against this vulnerability by Digital Vaccine protection filter ID 5328. For further product information on the TippingPoint IPS:

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:

Disclosure Timeline

    2007-02-15 - Vulnerability reported to vendor
    2007-05-02 - Coordinated public release of advisory

Credit

This vulnerability was discovered by: