VoIP Phones - Cisco 7xxx
Phones and Versions Tested
| Cisco 7xxx Versions tested | ||
|---|---|---|
| Model | Version | Notes |
| 7940 | 3.8.6 |
|
| 7940G | SIP41.8-5-4S | Appears stable
|
| 7940G | SIP41.9-4-2SR1-1S | Phone runs sluggish, reboots randomly, not recommended |
| Feature Notes | |
|---|---|
| Supports 302 Redirect | ? |
| Tested on FireBrick SIP Server | Yes |
| IPv6 Support | No |
* Important *
Whilst testing SIP41.8-5-4S it appears the phone/firmware is vulnerable to a SIP/UDP amplification attack where crafted SIP 'INVITE' packets sent on UDP 5600 cause the phone to respond to it's upstream SIP gateway with multiple SIP 2.0 '404' packets. Measured at a rate of approximately 20 packets/second, whilst not a major cause for concern with a single phone could potentially cause service issues where several phones are in use.
This vulnerability is protected against by correct firewall protection/filtering limiting inbound UDP on SIP port 5600 to the phone to be exclusively from the parent SIP service (e.g. voiceless.aa.net.uk - see the VoIP security/firewall section). It is not recommended to leave these phones connected to the internet without any protection.
Configuration:
Firewall & Security
- You will also want to set up firewall rules, as per the VoIP Firewall page.
- Also see the VoIP Security page for information about securing your VoIP service.