[NT] AGEphone "sipd.dll" SIP Packet Handling Buffer Overflow

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  AGEphone "sipd.dll" SIP Packet Handling Buffer Overflow
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SUMMARY

 <http://www.ageet.com/us/agephone/index.htm> AGEphone is "a SIP softphone 
written by Ageet". A vulnerability has been found in AGEphone. When 
exploited, the vulnerability allows execution of arbitrary code with 
privileges of the AGEphone user via a single specially-crafted UDP SIP 
packet.

DETAILS

Vulnerable Systems:
 * AGEphone for Windows version 1.24
 * AGEphone for Windows version 1.38.1

Immune Systems:
 * AGEphone for Windows version 1.40

This advisory discloses a buffer overflow vulnerability in AGEphone.

AGEphone uses the unsafe "sscanf()" function when processing a UDP SIP 
packet received via its SIP session port. This can cause a stack-based 
buffer overflow when a specially-crafted SIP packet is received.

The vulnerability occurs in "sipd.dll" in a function that resembles the 
following:
function_100115D0(char *receivedSIPdata)
{
 DWORD value;
 char buffer1[20];
 char buffer2[40];
 
 if(receivedSIPdata != NULL)
 {
  // Skip leading SPACE and TAB characters
  while(*receivedSIPdata != NULL)
  {
   if(*receivedSIPdata == 0x20 || *receivedSIPdata == 0x09)
    receivedSIPdata++;
   else
    break;
  }
  
  if(strnicmp(receivedSIPdata, "SIP/", 4) == 0)
  {
   // BUFFER OVERFLOW when string read into buffer1 or buffer2 is overly 
long!!!
   
   sscanf(receivedSIPdata, "%s %d %s\r\n", buffer1, value, buffer2);
   return value;
  }
  else if(strnicmp(receivedSIPdata, "INVITE", 6) == 0)
  {
   ...
  }
  else if(...)  // Other else-if statements to determine the SIP command
  {
  }
 }
}

Example SIP UDP packet that can trigger the buffer overflow:
SIP/AAAAAAAA[approx-68-bytes]AAAAAA 1 A
From: test
To: test

Or:

SIP/A 1 AAAAAAAA[approx-48-bytes]AAAAAA
From: test
To: test

Disclosure Timeline:
2006-07-21 - Vulnerability Discovered.
2006-07-22 - Initial Vendor Notification.
2006-07-24 - Vendor Released Fixed Version.
2006-07-25 - Public Release.


ADDITIONAL INFORMATION

The information has been provided by  <mailto:chewkeong@vuln.sg> Tan Chew 
Keong.
The original article can be found at:  
<http://vuln.sg/agephone1381-en.html> http://vuln.sg/agephone1381-en.html



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