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Comment by londons_explore | Hacker News Reader

While "call them back" is good practice, you should remember that even outgoing telephone calls aren't authenticated or encrypted. An advanced enough attacker can totally redirect your outbound calls too - it's just a little harder without an insider in your phone network.

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If your threat vector is someone hacking/infiltrating your phone network, you have bigger problems.

Perhaps orders of magnitude more likely than someone getting root on your telecom network is someone simply convincing you that an attacker's VOIP number is the official support number you wanted to call.

You shouldn't be downvoted because you're right, although for a slightly different reason. Scammers definitely have been using this trick: https://security.stackexchange.com/questions/100268/does-han...

So to be safe, I should call them back on a one-time use burner phone? What would you recommend for the call back?

What, and trust that they didn't compromise the hardware manufacturing supply chain? Not today, criminals! I design and construct my own one time burner phone from silicon I personally extracted and refined, it's the only way to be secure!

You have to find the address of the call center, and go there and ring their bell.

But don’t just google the location! The scammers are onto this now and have set up fake call centres and banking branches to trick you.

You need to start from a reasonable root of trust like your local government. Go down to city hall and ask them to pull the business license for the organization, and visit the address on file there and work your way down through the organization to the department you’re trying to contact.

> An advanced enough attacker can totally redirect your outbound calls

How?

The attacker rings your phone company up, impersonates you, and gets your phone line added to a company plan where all dialled phone numbers are first passed to a company phone system to allow the mobile phone to act like an internal phone - so for example you can dial "753" to ring the phone in room 753 of your company office. Calls will only go to the external phone network if the internal company one rejects them.

Then the attacker can intercept any outgoing call.

Feasible. Far more work required, and the plan switch should trigger all sorts of red flags (and thus verifications) before you even place a single phone call.

Is this even possible? An external number's calls getting routed around to the internal side of a PBX without explicitly dialing into the PBX?

Possible, you need to convince the phone company, but it is done just often enough for real reasons that it is posisble

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