[Giagnocavo]Michael::Write() - VoIP Security

Friday, October 10, 2008

VoIP Security - Peering

Every now and then I read an article on VoIP security. These articles almost always go over the obvious stuff such as lack of encryption, eavesdropping and ensuring you firewall your networks and so on. While certainly major issues, especially for a corporate deployment, there are still some other interesting issues.

One thing that keeps getting mentioned is the possibility for VoIP peering. Peering allows VoIP providers to send calls directly to each other (possibly over the Internet, maybe over [semi-]private connections). The main idea is cost savings, since the call doesn't need to go out over the public telephone network (PSTN).

To accomplish this, they'll set up a shared database mapping telephone numbers to VoIP providers. So, when a VoIP provider attempts to place a call, it'll consult this directory first. If it finds the number in there, it'll send it direct to the provider instead of over the PSTN. All the providers sign some sort of contract to say they'll be careful with the database and not populate it with invalid entries. Let's just assume the VoIP provider is trustworthy and hires trustworthy people (this is a stupid assumption, but I've had a peering company tell me this, as the security problems are too obvious without this assumption).

This system actually holds true inside of a VoIP provider's own network. A provider will want to terminate directly to a customer instead of out via the PSTN then back into their own network. So they'll probably have a directory of their own numbers so they can route those directly.

Well first off, now every peering member's security is bound by the security of every other member. If just one "trustworthy" peering provider gets compromised (not a hard task - more on that later), they can pollute the shared directory and hijack phone numbers. Being able to redirect a financial institution's phone number sounds like a profitable attack. An attacker can simply route the call to their system, then pass it through to the PSTN to avoid detection by users. Note that none of the security technologies available can prevent problems with a subverted, trusted, directory.

But it gets easier...
Many providers let you port your existing number to them when you sign up. From my limited experience, I've seen some of them immediately activate the number for you, so you can get started and going with their network while the port happens. A port can take a bit of time (and for now, let's assume the porting system is secure), so this sounds like a reasonable approach.

Wrong. First off, the new customer's number will probably go right into the provider's internal database, so all calls from that provider will go to the ~~customer~~ attacker. Depending on the size of the provider, this could be a pretty decent attack in and of itself.

But now, suppose the peering contract didn't specify not provisioning ports-in-progress, or if it did, the implementation people messed up. Now ALL the VoIP providers have been compromised, by a single provider who was agressive in their porting tactics.

Eventually it'll probably get resolved, but even a few hours or days of compromising a valuable phone number can be a significant attack.

What's the threat?
As a consumer, in general, I'd not worry too much about people trying to tap my line, just like I rarely worry about the safety of my wired Internet connection. But similar to intercepting credit card info versus hacking a company's database, this is a much juicier target. An attacker who pulls this off gets access to bulk information. Thus, I think the threat of something like this happening is much higher than having my individual calls monitored.

Security | VoIP

Friday, October 10, 2008 12:25:14 AM UTC

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