introduction to svmap
Last updated: Oct 24, 2020
Svmap is a network scanner for SIP. Similar to nmap - it will scan for devices on ports specified by passing the right command line options. Once svmap finds a device that supports SIP, it will extract information from the response and identify the type of device. Anyone running this tool will typically end up with a list of IP addresses of SIP devices and the names for those devices.
A penetration tester or security auditor will probably find this tool particularly useful especially during reconnaissance. With the IP address, device name and possibly version at hand, he or she can then target security weaknesses specific to that device. A security administrator or security analyst can also make use of svmap to list different active SIP user-agents on the network. Based on this information, the security administrator then has the ability to identify rogue and vulnerable devices which can cause a security concern.
Svmap is able to scan for SIP devices much faster than generic UDP port scanners. Typical port scanners such as nmap, scan UDP ports by sending a packet to each port and expecting an ICMP packet which indicates that the port is closed. If no ICMP error is received within a reasonable time, the port scanner assumes that the port is either open or else filtered. While this method has worked for years, it can never be considered efficient or neat, (at least) because of two reasons:
- The majority of UDP ports are closed - therefore having to wait for each ICMP error to confirm that the port is closed is not a good idea
- Nowadays a lot of devices are behind firewalls or NAT and will never reply with an ICMP error
Svmap works by sending a UDP packet containing a SIP request to a range of specified IP addresses, and listing those that send back a valid SIP response. Since UDP is a connectionless protocol, this method can be relatively fast. For example, during testing we were able to identify around 200 SIP devices on one particular network, out of a scan of IP addresses in less than 3 minutes. On the other hand when we scanned the same network with nmap version 4.20 (default options for sU scan on port 5060), it took longer than 20 minutes at which point we stopped the scan.