Update: Virgin fixed the issue Tuesday night after taking their login page down for four hours. Please see my update at the bottom of this post.
I reported the issue to Virgin Mobile USA a month ago and they have not taken any action, nor informed me of any concrete steps to fix the problem, so I am disclosing this issue publicly.
Virgin Mobile forces you to use your phone number as your username, and a 6-digit number as your password. This means that there are only one million possible passwords you can choose.
This is horribly insecure. Compare a 6-digit number with a randomly generated 8-letter password containing uppercase letters, lowercase letters, and digits - the latter has 218,340,105,584,896 possible combinations. It is trivial to write a program that checks all million possible password combinations, easily determining anyone’s PIN inside of one day. I verified this by writing a script to “brute force” the PIN number of my own account.
Once an attacker has your PIN, they can take the following actions on your behalf:
Read your call and SMS logs, to see who’s been calling you and who you’ve been calling
Change the handset associated with an account, and start receiving calls/SMS that are meant for you. They don’t even need to know what phone you’re using now. Possible scenarios: $5/minute long distance calls to Bulgaria, texts to or from lovers or rivals, “Mom I lost my wallet on the bus, can you wire me some money?”
Purchase a new handset using the credit card you have on file, which may result in $650 or more being charged to your card
Change your PIN to lock you out of your account
Change the email address associated with your account (which only texts your current phone, instead of sending an email to the old address)
Change your mailing address
Make your life a living hell
How to protect yourself
There is currently no way to protect yourself from this attack. Changing your PIN doesn’t work, because the new one would be just as guessable as your current PIN. If you are one of the six million Virgin subscribers, you are at the whim of anyone who doesn’t like you. For the moment I suggest vigilance, deleting any credit cards you have stored with Virgin, and considering switching to another carrier.
What Virgin should do to fix the issue
There are a number of steps Virgin could take to resolve the immediate, gaping security issue. Here are a few:
Allow people to set more complex passwords, involving letters, digits, and symbols.
Freezing your account after 5 failed password attempts, and requiring you to identify more personal information before unfreezing the account.
Requiring both your PIN, and access to your handset, to log in. This is known as two-step verification.
In addition, there are a number of best practices Virgin should implement to protect against bad behavior, even if someone knows your PIN:
Provide the same error message when someone tries to authenticate with an invalid phone number, as when they try to authenticate with a good phone number but an invalid PIN. Based on the response to the login, I can determine whether your number is a Virgin number or not, making it easy to find targets for this attack.
Any time an email or mailing address is changed, send a mail to the old address informing them of the change, with a message like “If you did not request this change, contact our help team.”
Require a user to enter their current ESN, or provide information in addition to their password, before changing the handset associated with an account.
Add a page to their website explaining their policy for responsible security disclosure, along with a contact email address for security issues.
History of my communication with Virgin Mobile
I tried to reach out to Virgin and tell them about the issue before disclosing it publicly. Here is a history of my correspondence with them.
August 15 – Reach out on Twitter to ask if there is any other way to secure my account. The customer rep does not fully understand the problem.
August 16 – Brute force access to my own account, validating the attack vector.
August 15-17 – Reach out to various customer support representatives, asking if there is any way to secure accounts besides the 6-digit PIN. Mostly confused support reps tell me there is no other way to secure my account. I am asked to always include my phone number and PIN in replies to Virgin.
August 17 – Support rep Vanessa H escalates the issue to headquarters after I explain I’ve found a large vulnerability in Virgin’s online account security. Steven from Sprint Executive and Regulatory Services gives me his phone number and asks me to call.
August 17 – I call Steven and explain the issue, who can see the problem and promises to forward the issue on to the right team, but will not promise any more than that. I ask to be kept in the loop as Virgin makes progress investigating the issue. In a followup email I provide a list of actions Virgin could take to mitigate the issue, mirroring the list above.
August 24 – Follow up with Steven, asking if any progress has been made. No response.
August 30 – Email Steven again. Steven writes that my feedback “has been shared with the appropriate managerial staff” and “the matter is being looked into”.
September 4 – I email Steven again explaining that this response is unacceptable, considering this attack may be in use already in the wild. I tell him I am going to disclose the issue publicly and receive no response.
September 13 – I follow up with Steven again, informing him that I am going to publish details of the attack in 24 hours, unless I have more concrete information about Virgin’s plans to resolve the issue in a timely fashion.
September 14 – Steven calls back to tell me to expect no further action on Virgin Mobile’s end. Time to go public.
Update, Monday night
Sprint PR has been emailing reporters telling them that Sprint/Virgin have fixed the issue by locking people out after 4 failed attempts. However, the fix relies on cookies in the user’s browser. This is like Virgin asking me to tell them how many times I’ve failed to log in before, and using that information to lock me out. They are still vulnerable to an attack from anyone who does not use the same cookies with each request. (ed: This issue has been fixed as of Tuesday night)
This vulnerability only affects Virgin USA, to my knowledge; their other international organizations appear to only share the brand name, not the same code base.
Update, Tuesday night
Virgin’s login page was down for four hours from around 5:30 PDT to 9:30 PDT. I tried my brute force script again after the page came back up. Where before I was getting 200 OK’s with every request, now about 25% of the authentication requests return 503 Service Unavailable, and 25% return 404 Not Found.
Virgin took down their login page for 4 hours Tuesday night to deploy new code. Now, after about 20 incorrect logins from one IP address, every further request to their servers returns 404 Not Found. This fixes the main vulnerability I disclosed Monday.
I just got off the phone with Sprint PR representatives. They apologized and blamed a breakdown in the escalation process. I made the case that this is why they need a dedicated page for reporting security and privacy issues, and an email address where security researchers can report problems like this, and know that they will be heard.
I gave the example of Google, who says “customer service doesn’t scale” for many products, but will respond to any security issue sent to email@example.com in a timely fashion, and in many cases award cash bounties to people who find issues. Sprint said they’d look into adding a page to their site.
Even though they’ve fixed the brute force issue, I raised issues with PIN based authentication. No matter how many automated fraud checks they have in place, PIN’s for passwords are a bad idea because:
people can’t use their usual password, so they might try something more obvious like their birthday, to remember it.
Virgin’s customer service teams ask for it in emails and over the phone, so if an attacker gains access to someone’s email, or is within earshot of someone on a call to customer service, they have the PIN right there.
If I get access to your PIN through any means, I can do all of the stuff mentioned above – change your handset, read your call logs, etc. That’s not good and it’s why even though Google etc. allow super complex passwords, they allow users to back it up with another form of verification.
I also said that they should clarify their policy around indemnification. I never actually brute forced an account where I didn’t know the pin, or issue more than one request per second to Virgin’s servers, because I was worried about being arrested or sued for DOSing their website. Fortunately I could prove this particular flaw was a problem by dealing only with my own account. But what if I found an attack where I could change a number in a URL, and access someone else’s account? By definition, to prove the bug exists I’d have to break their terms of service, and there’s no way to know how they would respond.
They said they valued my feedback but couldn’t commit to anything, or tell me about whether they can fix this in the future. At least they listened and will maybe fix it, which is about as good as you can hope for.