Reg probe bombshell: How we HACKED mobile voicemail without a PIN

Months after Leveson inquiry, your messages are still not secure


Special report Voicemail inboxes on two UK mobile networks are wide open to being hacked. An investigation by The Register has found that even after Lord Leveson's press ethics inquiry, which delved into the practice of phone hacking, some telcos are not implementing even the most basic level of security.

Your humble correspondent has just listened to the private voicemail of a fellow Reg journalist's phone, accessed the voicemail inbox of a new SIM bought for testing purposes, and the inbox of someone with a SIM issued to police doing anti-terrorist work. I didn’t need to use nor guess the login PIN for any of them; I faced no challenge to authenticate myself.

There was a lot of brouhaha over some newspapers accessing people's voicemail without permission, but one of the strange things about it all is that at no stage have any fingers been pointed at the mobile phone networks for letting snoops in. And some doors are still open.

Photo by Keven Law

Charlotte Church ... tabloid tapped her inbox (source)

It's believed the infiltrated inboxes merely had default PINs, or passcodes that were far too easy to guess, allowing eavesdroppers to easily drop by. People were urged to change their number codes for their voicemail, but, as we shall see, that advice is useless – you simply don't need to know a PIN to listen to someone's messages.

Going down the rabbit hole

The login flaw was discovered during development work I was doing on a virtual mobile phone network that's aimed at folks who struggle with modern technology: it allows, for example, an elderly subscriber to ring up a call centre and ask to be put through to a friend or relative, rather than flick through a fiddly on-screen contacts book.

In this case, the operator makes the connection between the subscriber and the intended receiver, but the "calling line identification" (CLI) shown at the receiving end is that of the subscriber and not of the call centre. CLI is the basis of caller ID in the UK, but it's a bit of a misnomer because it can be changed as required.

I’d long suspected that miscreants were hacking voicemail by spoofing their CLIs to fool the phone system into thinking it was the handset collecting the messages – but surely that's too easy? It is trivial to set an arbitrary CLI when making a call. I had to find out if voicemail systems were vulnerable to spoofing.

I was emboldened by an email from Register reader Sebastian Arcus, who had set up some software for making voice calls over the internet (VoIP in other words) using his mobile phone number, and was surprised that he was able to collect his voicemail from his VoIP client without having to hand over an access PIN. I was further goaded in a chat in the pub with a Reg colleague, who bet me I couldn’t hack his voicemail. I should’ve asked for money to back that one up.

How it should work and how it falls apart

If you call your voicemail service from a handset linked to the account, you go through to your message inbox without the need to enter a PIN, presumably as a convenience. Use any other phone and you are asked for a PIN access code. If there is no PIN set, you don’t get to the voicemail. So far, so good.

The special sauce here is how does the mobile phone network know which phone you are calling from? The easy way is to look at the CLI sent when establishing a call.

Unfortunately, as our reader found out, this caller identification isn’t at all secure and can be spoofed, so we looked at Three, EE (and Orange), O2 and Vodafone.

Similar topics


Other stories you might like

  • Battlefield 2042: Please don't be the death knell of the franchise, please don't be the death knell of the franchise

    Another terrible launch, but DICE is already working on improvements

    The RPG Greetings, traveller, and welcome back to The Register Plays Games, our monthly gaming column. Since the last edition on New World, we hit level cap and the "endgame". Around this time, item duping exploits became rife and every attempt Amazon Games made to fix it just broke something else. The post-level 60 "watermark" system for gear drops is also infuriating and tedious, but not something we were able to address in the column. So bear these things in mind if you were ever tempted. On that note, it's time to look at another newly released shit show – Battlefield 2042.

    I wanted to love Battlefield 2042, I really did. After the bum note of the first-person shooter (FPS) franchise's return to Second World War theatres with Battlefield V (2018), I stupidly assumed the next entry from EA-owned Swedish developer DICE would be a return to form. I was wrong.

    The multiplayer military FPS market is dominated by two forces: Activision's Call of Duty (COD) series and EA's Battlefield. Fans of each franchise are loyal to the point of zealotry with little crossover between player bases. Here's where I stand: COD jumped the shark with Modern Warfare 2 in 2009. It's flip-flopped from WW2 to present-day combat and back again, tried sci-fi, and even the Battle Royale trend with the free-to-play Call of Duty: Warzone (2020), which has been thoroughly ruined by hackers and developer inaction.

    Continue reading
  • American diplomats' iPhones reportedly compromised by NSO Group intrusion software

    Reuters claims nine State Department employees outside the US had their devices hacked

    The Apple iPhones of at least nine US State Department officials were compromised by an unidentified entity using NSO Group's Pegasus spyware, according to a report published Friday by Reuters.

    NSO Group in an email to The Register said it has blocked an unnamed customers' access to its system upon receiving an inquiry about the incident but has yet to confirm whether its software was involved.

    "Once the inquiry was received, and before any investigation under our compliance policy, we have decided to immediately terminate relevant customers’ access to the system, due to the severity of the allegations," an NSO spokesperson told The Register in an email. "To this point, we haven’t received any information nor the phone numbers, nor any indication that NSO’s tools were used in this case."

    Continue reading
  • Utility biz Delta-Montrose Electric Association loses billing capability and two decades of records after cyber attack

    All together now - R, A, N, S, O...

    A US utility company based in Colorado was hit by a ransomware attack in November that wiped out two decades' worth of records and knocked out billing systems that won't be restored until next week at the earliest.

    The attack was detailed by the Delta-Montrose Electric Association (DMEA) in a post on its website explaining that current customers won't be penalised for being unable to pay their bills because of the incident.

    "We are a victim of a malicious cyber security attack. In the middle of an investigation, that is as far as I’m willing to go," DMEA chief exec Alyssa Clemsen Roberts told a public board meeting, as reported by a local paper.

    Continue reading

Biting the hand that feeds IT © 1998–2021