VoIP: SIP-over-TLS and sRTP: Avantec

A VoIP/SIP-based phone is nothing else than a computer. Although a desk phone has only one application, calling, a whole computer is required. Which operating system should one go? Who cares about the operating system? Who cares about the device drivers and their integration into that operating system? In the Netherlands, a company called Dialog Semiconductor (former SiTel Semiconductor) made a VoIP/SIP chipset including software stack called Rhea. That is based on μClinux. That sounds like a great idea in marketing papers. Does anyone care about that μClinux and apply the latest security findings? And who? Does anyone care about Rhea and apply the latest security findings? And who? When one link in that chain stops to do his work, the whole platform dies. For another former Rhea user, vTech, buying a whole different manufacturer was easier than to repair their platform. Go figure!

Last tested firmware

30 Jun, 2015

Configuration

Password: Admin: avantec/admin
User: user/1111
Phone: admin (center soft-key switches charset)
Web → Admin → Set Password
HTTPS: not available
Update: Web → Admin → Upgrade
Trust Anchors: not tested
SIP-URI User: Web → Configuration → SIP Accounts → Register Name
Web → Configuration → SIP Accounts → User Id
SIP-URI Host: Web → Configuration → SIP Accounts → Registrar IP: FQDN works
SIP-over-TLS: Web → Configuration → SIP Settings: TLS
does nothing in my tests, TCP did DNS-A only and no connection; use UDP instead
SDES-sRTP: Web → Configuration → Audio Settings → SRTP Mode: Optional (only for incoming)
which is RTP/SAVP

Bad Defaults

These features are disabled on default, although they are automatically negotiated. Tests revealed they work. Therefore, no reason exists to disable those on default.

Session Timers: Web → Configuration → SIP / NAT Settings
UPDATE: Web → Configuration → SIP / NAT Settings
PRACK: Web → Configuration → SIP / NAT Settings

Software Bugs

IPv6: broken
Phone does only DHCPv4 as with IPv4. It does not DNS-A but DNS-AAAA. However, that is not done on the VoIP server address but on its own IPv4 address. Go figure!
DNS-SRV: missing for TCP and TLS; therefore DNS-NAPTR useless
Audio: G.726-32 has the wrong endianness
Mitigation: set ‘g726nonstandard=yes’ in your Digium Asterisk
DiffServ: not enabled on default
Mitigation for RTP: Web → Audio → ToS: 184

Security

Bugs: SIP-over-TLS does nothing in my tests.
TCP did at least DNS-A but no connection as well. I had to use UDP. If you use UDP, the SDES-sRTP key is transferred in plain text providing no added security.
Responsible Disclosure: not required
Firmware Update: missing Automation
missing Newsletter

Miscellaneous

Model Range

Power Supply

9 V 0.5 A, Coaxial: 5.5 mm × 2.1 mm

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