CVE:CVE-2007-5583
CNNVD:CNNVD-200712-207
Cisco 7940型IP电话是一种多功能通讯设备，通过IP网络传递语音信号。
Cisco 7940在处理畸形INVITE消息时存在漏洞，远程攻击者可能利用此漏洞导致设备不可用。
如果向Cisco 7940 IP电话发送了一系列SIP INVITE消息的话，就可能导致设备看起来在正常工作而实际上无法接收或发起呼叫，继续发送INVITE消息的话就会导致设备重启。 
攻击者所发送的SIP INVITE消息中的Request-URI部分应不包含有用户名，如INVITE sip:XXX.XXX.XXX.XXX SIP/2.0。需要发送6次才能导致设备拒绝服务，如下所示： 
X ----------------------- INVITE (Call-ID #1) -----------------------> Cisco 7940
X <------------------ 100 Trying (Call-ID #1) --------------------- Cisco 7940
 ....
--------5 New Dialogs like the previous--------
 ....
X ----------------------- INVITE (Call-ID #7) -----------------------> Cisco 7940
X <------------------ 486 Busy (Call-ID #7) --------------------- Cisco 7940
-------- DoS for aproximatly 3 minutes ------
X <------------------ 486 Busy (Call-ID #1) --------------------- Cisco 7940 
X <------------------ 486 Busy (Call-ID #2) --------------------- Cisco 7940 
X <------------------ 486 Busy (Call-ID #3) --------------------- Cisco 7940
X <------------------ 486 Busy (Call-ID #4) --------------------- Cisco 7940
X <------------------ 486 Busy (Call-ID #5) --------------------- Cisco 7940 
X <------------------ 486 Busy (Call-ID #6) --------------------- Cisco 7940
solution:Upgrade cisco ip_phone_7940 to a higher version than *:firmware_p0s3-08-7-00,and avoid the version *:firmware_p0s3-08-7-00