A vulnerability in ParseExtension() function in openslp was reported. Attacker can force the function to enter the infinte loop causing denial of service via packet with crafted "nextoffset" value and "extid" value.

Vulnerable code in openslp-1.2.1/common/slp_message.c:


int ParseExtension(SLPBuffer buffer, SLPMessage message)

/* Parse extensions *after* all standard protocol fields are parsed
*/

/*--------------------------------------------------------------------------*/

{
	int extid;
	int nextoffset;
	int result = SLP_ERROR_OK;
	extoffset = message->header.extoffset;
	while(nextoffset)
	{
		//here,buffer->start value is stable ,and we can
		control nextoffset,so we can control buffer->curpos
		buffer->curpos = buffer->start + nextoffset;
		if(buffer->curpos + 5 >= buffer->end)
		{
			/* Extension takes us past the end of the buffer */
			result = SLP_ERROR_PARSE_ERROR;
			goto CLEANUP;
		}
		extid = AsUINT16(buffer->curpos);
		buffer->curpos += 2;
		//here,wo can control nextoffset by make a crafted packet
		nextoffset = AsUINT24(buffer->curpos);
		buffer->curpos += 3;
		switch(extid)
		{
			case SLP_EXTENSION_ID_REG_PID:
			if(message->header.functionid == SLP_FUNCT_SRVREG)
			{
				/* check to see if buffer is large enough to contain the 4
				byte pid */
				if(buffer->curpos + 4 > buffer->end)
				{
					result = SLP_ERROR_PARSE_ERROR;
					goto CLEANUP;
				}
				message->body.srvreg.pid = AsUINT32(buffer->curpos);
				buffer->curpos += 4;
			}
			break;
			default:

			if (extid >= 0x4000 && extid <= 0x7FFF )
			{
				/* This is a required extension. We better error out */
				result = SLP_ERROR_MESSAGE_NOT_SUPPORTED;

				goto CLEANUP;

			}
			break;
		}

	}
	CLEANUP:
	return result;
}