Your problem is not with SMS as a second factor though. (Unless you think the attacker had your password as well). It is with the use of SMS as a single recovery factor.
The very things that make SMS a uniquely good second factor make it an awful only factor. Use of SMS for account recovery should in general (or at least for important accounts) have a delay (order of days) that allows the real user to intervene.
If the argument is "but you still have a password" it really kind of shows how weak SMS 2FA is. Compare that to a U2F token where you can very reasonably remove the password entirely and still be just as safe - it is itself just a strong auth mechanism, whereas SMS is adding extremely questionable value between the ability to phish SMS 2FAs or hijack the number.
Even in a situation where the attacker would have needed the password too, consider how much more vulnerable you are now that they have a significant piece of your auth - could they leverage that to social engineer an account recovery?
Phone numbers are terrible at conveying identity, unfortunately, so bringing them into the "who are you" heuristic is kinda just a net loss.
> Compare that to a U2F token where you can very reasonably remove the password entirely and still be just as safe
Yeah, and it requires me to use a U2F token, which I can loose, etc. You have to balance security and usability, and SMS as a second factor seems like a perfectly reasonable balance.
I witnessed so many people lose access to their accounts because they wiped their phone that had an authenticator app, or they lost their physical 2FA tool.
1. You increase the risk of losing your entire life (if 2FA is properly implemented and avoids all social engineering process risks)
or
2. The 2nd factor devolves into a 2nd way to get access to your account
You really can't have both security and convenience.
> wiped their phone that had an authenticator app
try this one: battery dies in an iPhone. iPhone won't boot until battery is replaced. Battery can only be replaced at an Apple store. 2FA: do you feel lucky, punk?
Services like Authy address some of the loss of device issue, and always a good idea to have a backup token (e.g., yubikey) physically escrowed somewhere like a safe-deposit box.
But it is a whole lot of extra work to set up and maintain long-term, even with the best intentions.
+1 for Authy. Just get a used cheap Android phone for like $30 and use it as the backup device for Authy and never fear about losing your 2FA device again.
Does Authy actually offer 2FA? It sounds like the security boils down to your encryption passcode used to encrypt the 2FA secret, so you aren't actually using 2FA at the end of the day.
For personal use it probably is a good compromise for services which don't implement 2FA properly (that is to say, services that don't allow you to register multiple 2FA devices.) But realistically you might want to just disable 2FA and rely on your password manager.
I'm not sure what you meant by this, Authy certainly provides TOTP, and the encryption password is only used when you need to sync the 2FA secret to other devices, which by the way also requires confirmation using SMS to your phone number as well.
I usually take 2FA to mean that you have to use two of (something you have, something you know, or something you are.) If the "2FA secret" (TOTP secret?) is stored on multiple devices it doesn't actually prove ownership of "something you have" it's effectively no different from a password stored within a password manager which is considered simply "something you know." So basically the TOTP secret is a second password with some obfuscation that protects the password. But software running on one of your devices could easily steal the secret.
It does seem like this is somewhat more secure, in some sense, but it weakens the security that TOTP is intended to provide.
TOTP has always been a second password (heck, it's in the name). If you know the secret and the algorithm you can do the maths yourself in theory without needing any hardware, so in theory it can always be considered "something you know", even without all the syncing stuffs from Authy.
In any case I don't see how the Authy password can weaken TOTP. It's not like there's a webpage out there where you can enter the Authy password and it will give you back the TOTP secret for a specific user. It's only used to decrypt the TOTP secret if you choose to sync that secret to another new device, which again requires SMS verification, PLUS confirmation from an existing device, PLUS you need to have the sync capability setting enabled (so you can always sync the TOTP to your backup device first then disable the sync setting to prevent additional devices being synced).
Or just copy your TOTP codes to a second device without going via the internet.
I'm annoyed Google Authenticator makes it so easy to transfer accounts to a new phone, how will you know if someone's cloned your TOTP private key while you were sleeping?
Password managers such as 1Password and Bitwarden can save and fill in TOTP codes. Maybe not perfect security but a big win for convenience and loss prevention.
I have received advice from way to many people to not use your password manager as a 2nd factor be ause 1) It's actually become the only point if failure (your pw getting hacked). 2) Both factors protected and saved on the same spot
1Password in particular encrypts your vault with your master password and importantly an additional 128 bit secret key that is meant to be kept somewhere physically (e.g. in your safe). This key is needed the first time your vault is decrypted (e.g. a new device)
An attacker would need to have access to all of the following:
a) your encrypted vault
b) your master password
c) an 128-bit secret key
in order for the fears you've outlaid to be realised.
Really the only attack vector I can see is a physically compromised device (brute forcing is out of the question). In which case, they'd still need to somehow know your Master password and you're no more vulnerable considering your OTP is likely to be in an application on your phone anyway.
Since your own computer will typically have the vault unlocked, you don't need a+b+c. You can suffice with a circa 2000s Sony Music cd. Or any driveby malware, or malvertisement, etc.
Using the 2nd factor on another device as the first means attackers need to either compromise 2 devices, or compromise a single point higher up in the hierarchy (e.g., your google account).
If there’s malware on your PC that has complete access to your system memory you are screwed in every single way possible. I’m perfectly comfortable with having my OTP coupled with my passwords given this is the only real attack vector and requires an actively unlocked vault to expose secrets.
If this is the case, what’s stopping the malware from adding a key logger and MITMing your input to your bank’s website, Gmail or Coinbase?
> I also photograph the 2FA code or QR code and print it to a safe place.
This is really great advice.
I do something similar. I have a copy of the recovery codes (where possible) in an encrypted volume with multiple copies. Also printouts. The printouts have saved me once already.
Also, don't underestimate the utility of carrying around an encrypted SD card with things you want to retain access to!
And the site has to support U2F. U2F is a great standard but almost none of the businesses I interact with support it. There are maybe 3 banks in the US that support it, but not mine.
I don't understand why banks and businesses don't outsource the whole authentication business to someone that does nothing else, and then does proper 2FA (maybe with a choice of security levels), and supports as many standardised solutions as possible.
One of the problems here is that few sites support U2F, and even fewer support it properly.
Proper support would mean allowing multiple tokens, so that you can have one permanently on your keychain, one permanently in your computer at home, and an off site backup pair that you rotate (enroll the one that is at home, then swap and enroll the other one).
On desktop, touching a U2F token is a lot easier than typing numbers from a SMS, and it actually protects against one of the biggest threats, phishing (the SMS does not - if the phisher bothers to ask for it, the user, who thinks that they're logging into the legit web site, will enter it).
You can also "loose, etc" the phone so it is equally weak on that front. Except the SIM can be hijacked, so SMS is strictly worse and never better.
Best compromise between usability, access and recovery is to always use TOTP but be sure to always securely back up the secret offline. Don't ever just scan it into a single device, as then you're back to being able to lose it and be locked out.
The advantage with the phone is that the web site operator can pawn off the difficult recovery part on your mobile provider (go there, show ID, get a new SIM).
IMO both the mobile provider and the web site operator should be jointly liable for damages resulting from SMS 2FA abuse. The mobile operator for giving access to your phone number to an unauthorized person, the web site operator for using a known insecure technique.
Both the number of successful hijackings and companies using SMS 2FA would drop drastically.
Its generally not "second factor authentication" but 2-factor authentication. The idea is that you have 2 separate authentication factors. Preferably both with decent security.
Besides, I don't believe coinbase does SMS only account recovery. So here SMS really did fail as a second factor. Since it seems attackers must have had a password and SMS. (I am not 100% on the coinbase account recovery process)
No, it sounds like coinbase used email recovery, but his email provider used SMS recovery.
So the hacker only needed to hijack his SMS.... with that, they gained access to his email, and then with that gained access to coinbase. No password required.
SMS is better than nothing, but you have a bunch of other better fallback alternatives before you should rely on it. You can support the enrollment of multiple hardware tokens (i.e., you keep one at home, and one on your person). You can have online push login approvals. You can have a TOTP code generator.
TOTP is the one that makes the least sense to me. It is also weak to phishing (extremely common) but adds protection against SIM-swapping (comparatively very rare). It also has almost all of the downsides of U2F (a pain in the ass if you lose your device).
TOTP has the downsides of U2F, but those downsides are comparatively easier to mitigate.
Put a plan together for the "house burns down" scenario.
With U2F I need to enroll multiple tokens and keep some off-site. So what does this entail? I keep maybe 3 tokens, two on-site that I add the new account to, then on a regular schedule I rotate one off-site and bring the third one on-site and go back through and add it to any accounts I've created in the meantime? The whole process is a pain in the ass, and not all sites allow multiple devices to be registered (e.g., AWS). And new accounts are still vulnerable during the time between registering and rotating the third key on-site.
With TOTP you can... just sync your TOTP database. Some apps such as Microsoft Authenticator do this on their own. Personally, I put all my TOTP secrets into a Keepass database and sync it off-site with Nextcloud. There is no way for the site to limit how many devices I enroll so it's easy enough to create as many backup devices as you need. If you're really old school, you can print the secrets and put them in a fire safe.
FWIW, I have several yubikeys. I primarily use them as a secure store for TOTP secrets and to store a SSH key (generated off-device and backed up), not for webauthn. It's just too annoying to deal with in a way that ensures I don't lock myself out of an account.
Every modern TOTP app is cloud-synced, so I'm not sure why people are saying it's "a pain in the ass if you lose your device."
Heck, most modern password managers (e.g. 1Password, LastPass, etc.) are also TOTP, and help you fill the TOTP token (usually by putting in on your clipboard) at the same time they autofill the password.
> It is also weak to phishing (extremely common) but adds protection against SIM-swapping (comparatively very rare).
Sufficient paranoia / user training is enough to protect against phishing. (Especially for services where the only "users" are the extremely-paranoid IT admins themselves.) But nothing can really protect you from SIM-swapping, save for not allowing services that use single-factor SMS recovery to ever know your phone number in the first place.
(PITA, I know, but running little auth gateways like this is part-and-parcel of doing security for an org.)
> Considering how easily actual factual professional security engineers fall for phishing, I don't believe you.
It's almost always the service's fault for being designed in such a way that its real async user interactions are indistinguishable from phishing. You can't train a user to distinguish X from X.
• It's hard to train users to not forward TOTP tokens sent to them to someone else, if the real service will text or push-notifies the user their TOTP token "at random" (i.e. because the attacker tried to log in.) But if the service never does that — if you always have to go and fetch the token from your TOTP app — then you can just tell the user that the only time they are to go do that, is right after they've typed their username and password as part of logging in themselves; and that anything else is a phishing attempt.
• It's hard to train users to not type their username+password into phishing login pages, if the services you use constantly send you emails containing deep links. But if the service never does that — if the service always tells you to go your browser and navigate to the site yourself — then it's easy to teach users to never trust a login initiated through an email.
Security, in this case, is less about "good security hygiene", and more about priming/expectations. And because of that, the practice of being an IT admin for such an org, is a practice of picking services, or negotiating with services, to ensure that the service is following secure workflows when dealing with your users, so that your users can be trained.
I do use a similar approach to backup the Symantec secret - but what percentage of users do you think are capable of doing this? 0.1%?
> It's hard to train users to not forward TOTP tokens sent to them to someone else, if the real service will text or push-notifies the user their TOTP token "at random" (i.e. because the attacker tried to log in.) But if the service never does that — if you always have to go and fetch the token from your TOTP app — then you can just tell the user that the only time they are to go do that, is right after they've typed their username and password as part of logging in themselves; and that anything else is a phishing attempt.
A phishing attempt will do precisely this. You get a fake login page, type in your creds, and then you get a fake TOTP page.
> It's hard to train users to not type their username+password into phishing login pages, if the services you use constantly send you emails containing deep links. But if the service never does that — if the service always tells you to go your browser and navigate to the site yourself — then it's easy to teach users to never trust a login initiated through an email.
In a prior life I did some research on phishing. It is embarrassingly easy to fool even professional security researchers. Nobody is capable of consistently preventing phishing by using their own eyes and brain.
If you can manage a 100% policy of using no services that ever require users to do X, then you can also just disable doing X entirely through MDM. Phishing emails can't get your users if your users' email clients don't open links other than to whitelisted domains. :)
TOTP is an improvement over SMS in that identity is not tied to a phone number, which has been proven over and over again to be a terrible indicator of identity.
> You can support the enrollment of multiple hardware tokens (i.e., you keep one at home, and one on your person).
How many services do that today? And since so few people have fallbacks what is their recovery process like? Because the hackers will find the weaknesses.
WebAuthn explicitly tells Relying Parties (ie web sites) to all do this. All the services I use which offer WebAuthn or its predecessor U2F support multiple named hardware tokens and I enroll at least my Yubico branded device and one more at such sites. For those I use from a phone, the phone itself is enrolled.
AWS is the counter-example which will be (indeed already has been in this HN comment tree) cited as proof sites don't all do this, I've tried asking if there are literally any others, and never received any ideas. I don't currently have an employer and I don't use AWS for personal projects.
It's pretty common for sites that actually care about authenticating you (so, Google but not your Bank, GitHub but not your mortgage lender) to provide you with single use bypass codes which they tell you to write down and keep somewhere safe.
What about an authentication app? Google Authenticator or something similar can be installed on the phone which is necessary for SMS, improves the security more than SMS, and doesn't suffer from the problem of losing it, at least not more than SMS auth does.
When your phone is lost or stolen, you buy a new phone and go to your telco provider to get a new SIM with your number. SMS 2FA continues to work. Your Authenticator secrets are gone with the phone, and you're locked out.
(Unless you use a solution like Authy with multiple devices, which strikes me as the most sensible solution.)
It blows my mind that Google Authenticator still doesn't have a multi-device sync feature (or even a "recover from backup" feature on iOS for that app, because I think they added it recently to Android; just "recover from backup" alone would have been sufficient to convince me not to switch).
All of that made me switch to Microsoft Authenticator, as they do have both multi-device sync and "recover from backup" feature as well, so now I don't need to be stressed about my phone getting lost. Kind of sad, given that I've been a user of Google Authenticator for quite many years until that point.
I really wish that web browsers had worked on the UI for generating certificate signing requests and importing certificates and that websites had 2FA via username/password along with client-side TLS certificate for authentication.
This is more portable than U2F tokens since client-side certificates are part of the TLS standard and should be supported regardless of the application protocol used. Adding other devices could be done by sending a CSR along with the username and password and authorizing the second device from first device that's already logged into the account.
But Mozilla, and Google double teamed to sink it in W3C to push their own bicycle reinvention attempts, which after 10+ years, multiple incompatible versions, and errata ridden revisions are still not there.
Yes! This was a very good solution. Built right into the browser, very convenient. We built a related CA product back in the 90s and were issuing client certs on smarts cards via the browser. Plug in smartcard and browser could automatically authenticate to all services. Take it out and go home.
I used an SSL CA (Startcom / StartSSL) that used Client certs as its (only?) method of authentication. It was a terrible experience if you ever had to log in from another browser.
> Yeah, and it requires me to use a U2F token, which I can loose, etc.
In which case there are much safer recovery mechanisms available. For example, a second U2F token, or handwritten backup codes.
> and SMS as a second factor seems like a perfectly reasonable balance.
My point is that it isn't. Unfortunately, today, identity is a true privilege - it pretty much requires purchasing multiple U2F tokens, and that's super shitty. That doesn't mean that SMS 2FA is a good idea - the fact that it can actually reduce your security is very problematic.
But that is my entire point. SMS as a second factor is purely additive. It cannot reduce security.
There is pretty much no form of second factor that users are worse at passing than backup codes. Even if people print them out (few do), they won't find them when the emergency happens. You need some form of trust that can be bootstrapped again from scratch.
For most of the world, SMS is it. The Nordic countries have the bank if system. But the market is too small. Hopefully the EU-wide identity verification systems solve the scale problem.
> Some form of trust that can be bootstrapped again from scratch.
This is not using it as a second factor. It is using it as the only factor.
Having SMS as the only factor is not purely additive. As such it can (and obviously does) reduce security.
Account recovery is hard, SMS is quite usable there, but way to insecure to be the only basis for bootstrapping account recovery.
I don't really understand why you think I'm advocating for SMS as the only factor, when I very clearly wrote the exact opposite.
Let's say that you remember your password, but your house just burned down. You cannot replace the U2F keys and backup codes that were lost in flames. But you almost certainly can bootstrap your real life identity far enough to get a replacement SIM.
Which, in combination with your password, should be enough to get your digital identity back.
Except in practice, most providers (even those that should know better, like Google) allow use of SMS, ostensibly set up as a “second factor,” to be used for account recovery without knowing the password. Making it, in practice, 1FA.
Confusion about the word bootstrapping. I read "bootstrapping trust" as regaining trust based solely on SMS.
But indeed, sms as a second factor is much easier to recover in catastrophic situations than some other second factors. That is a fair point, and an advantage of sms over other common second factors.
> SMS as a second factor is purely additive. It cannot reduce security.
You are forgetting social engineering. Humans find it reassuring that the security process happened as usual, even if in fact the apparently "usual" process was them being being phished. This can mean they're actually less alert than they would be otherwise.
You get an urgent message from your bank about an unexpected $500 transaction, you follow the link & you need to enter your password as usual of course, and then it tells you that you'll get an SMS and to type in the code so you do so. Phew! Disaster averted! Right? This must have been real, you even got an SMS from the bank.
Alas the SMS was from your bank, and the bad guys didn't have a way to intercept it, but they didn't need one because you typed it into their phishing website. That unexpected $500 transaction wasn't real, but their emptying of your bank account will be.
"You get an urgent message from your bank about an unexpected $500 transaction, you follow the link & you need to enter your password as usual of course. It was a phishing website. Your bank account will be emptied."
But in your revised story I don't receive reassurance that everything is going as planned. That's what I'm getting at, the SMS step is reassuring even though it actually shouldn't be.
If there is no 2FA, not being asked for a confirmation code is things going as normal. Also, it's totally irrelevant whether the user gets cold feet since in the password-only world they've just handed away the keys to the kingdom.
> But that is my entire point. SMS as a second factor is purely additive. It cannot reduce security.
It most certainly can reduce security, that's the point. If I don't have a phone number on my account (which I almost universally don't) then no amount of SMS hijacking will ever matter.
If some provider forces me to put a phone number in, now I may be vulnerable to a weakness I didn't want to be vulnerable to. Maaybe today that particular provider uses SMS in a stricly additive sense. Maybe. Just as likely next month they'll redesign their site to be "easier" and add back the vulnerability.
Same with recovery questions. They make the security stricly worse for most people since they are password-equivalents with far lower entropy. Although personally my best friend from high school was named D3ho9WvylJkws1zfAKUxZjdYuCsS.
They specifically said "SMS as a second factor." What you're discussing here is a completely different different use of SMS that nobody is arguing in favor of.
As I mentioned, there is no guarantee any site is going to never allow use of that phone, once it's on file, to bypass authentication. Even if they don't right now. So adding a phone to an account increases your risk in a way you can't control. The only guaranteed way to avoid it is to never have a phone# on file.
> SMS as a second factor is purely additive. It cannot reduce security.
I responded to this in another post.
> There is pretty much no form of second factor that users are worse at passing than backup codes.
Agreed, I also mentioned backup U2F. At this point modern smart phones package TPMs that can also do attestation, so we're really not too far away from being in a situation where the vast majority of people have a U2F token in their pocket.
> In which case there are much safer recovery mechanisms available. For example, a second U2F token, or handwritten backup codes.
Which have either higher costs or "administrative burden" or both which will lead them to failure for a big chunk of non tech-savvy people. Educating a casual user that they need to print out recovery codes and store them in a safe place it's not exactly top notch usability.
Yes, as I've said, availability is the problem to solve. We should be shipping U2F tokens wherever we can. I'd like to see schools that require students to use GSuite and other U2F supporting sites giving students tokens for free. I'd like to see banks giving their customers tokens. I'd like to see companies giving them to employees.
IMO the problem is not "let's get some kind of 2FA" it's "let's get U2F in the hands of as many people as we can".
> The only way it can ever actively reduce your security is if it's used as a single factor, as it was for the OP.
I don't believe this is true. If I have your SMS I am considerably more likely to be able to phish a recovery, even if recovery also involves something else. Every piece of information the attacker can get is valuable for forging auth.
What SMS is good at is being available. At this point cell phones are distributed to a massive portion of the world. But at this point smartphones can also act as U2F devices, I believe, so I'm not sure that benefit is so meaningful anymore.
Instead of companies wasting time on SMS 2FA they should be figuring out how to help their customers set up U2F.
I'd like to avoid being in a situation in 10 years where we have great options for end users available but 2FA SMS is still supported for legacy reasons, and unwitting users end up using it because it seems easier and they don't understand the risks.
> I don't believe this is true. If I have your SMS I am considerably more likely to be able to phish a recovery, even if recovery also involves something else.
So it's better to not consider that information at all?
What is better? (1) Requiring a password to login or (2) Requiring a password and a code sent via SMS?
The problem you're describing is that services accept SMS in leu of other forms of verification, such as an actual password. Personally, I would very much like it if I could turn off any and all forms of "I forgot my password" flows. There should at minimum be a one-week waiting period or similar.
> So it's better to not consider that information at all?
Exactly
> What is better? (1) Requiring a password to login or (2) Requiring a password and a code sent via SMS?
They're equivalent in my mind - SMS is such a weak 2FA mechanism, and it's so easy to get wrong and have it decrease your overall security, any benefit is lost. Rather than pushing SMS because it's what we have we should make greater efforts to leverage technology that we know is considerably better in every regard except availability today - IMO that is the problem to solve.
SMS adds friction to password stuffing. Given that a gazillion people do not use unique passwords, this has some value.
It is possible that if we spent more time as a community encouraging the use of password managers that the net improvement in security posture would be greater, but this does remain a nontrivial benefit of SMS.
If you have strong generated passwords that are different for each system and you use password manager then you would not need 2FA at all. Well maybe if it is for system that stores your password in plain text but who would be stupid to keep user password in plain text and slap 2FA on top of it.
U2F and 2FA came to life just because people are bad at making passwords and remembering them.
Making non technical people to use password manager with generating passwords for each page is still hard.
Making non technical people use SMS as a second factor is easy.
Making non technical people use tokens is still hard.
There is a lot of value in having SMS 2FA still, yes you can phish it or you can hijack the number. But that is argument like: "there is no point in having any security at all because if you install malware on your computer you will get hacked".
Yes SMS alone is not going to save you, but people have phones and understand that they type code that comes via SMS to the phone number they provided when registering. Barrier to entry for it is so trivial that I think it still has value.
Barrier to entry to take over someones phone is not high but random kid on the street is not going to do that just like random kid that can find your email + de-hashed password from database dumps.
If you have someone who is motivated to get you then probably given enough time they will get you anyway.
So take into account what that SMS 2FA prevents and what issues it is solving. Don't just throw it away.
Hahahaha you would be surprised my current employer is thinking of introducing 2FA and yeah every pass is stored in plain text. I've been trying to make them change this for years, also the passwords are limited to 20 chars yeah.... security is shit here
It might be confusing but that was account recovery attack.
For account recovery there is no "password" as thieves just made their own password while having victim phone number.
So phone number as a password recovery option is not secure without any additional checks. Not 2FA because with this attack there was no second factor.
> Compare that to a U2F token where you can very reasonably remove the password entirely and still be just as safe
Not only that, but you can remove the username too: WebAuthn supports a "usernameless" mode where you press "login", touch your authenticator and you're in.
Sure, but that's why you add multiple devices/keys to your account. Reinstalling the OS should be fine.
I'm very much looking forward to password managers acting as soft-WebAuthn tokens so they can hold a simple private key and log you in to sites automatically by answering the login request. That way, you only need to unlock your password manager and you can log in to any site without a u/p.
Just don't get your password manager stolen, I guess, but that's already the case.
I've posted before on here about my experience getting SIM swapped and how quickly someone was able to gain access to a bunch of my accounts. If I hadn't been at home and looking at my phone while it was happening, it could have been much worse, but thankfully I was able to get in and terminate most of their login sessions before too much damage was done.
The one thing I distinctly remember was two of my GMail accounts starting the recovery process. Thankfully, that process apparently gives either 14 or 30 days to stop the recovery and secure my own account. Had I not been connected, that may have been my only saving grace, as I was able to secure those accounts and subsequently use them to recover other compromised accounts.
The larger lesson for me was to always use TOTP tokens where possible over SMS, and to completely disable SMS recovery for accounts that didn't have a delay on SMS-only recovery.
This. SMS is a great second factor and is perfectly suitable to prevent the main attack that you want second factors to prevent: that is if your password appears in a password list for any reason it should stopp anyone from just running away with your account. Note that if you are targeted directly SMS is not going to help you much but in this case maybe your password can (depending on the capabilities of the attacker).
Now is SMS the best second factor? Of course not and a proper U2F token will be a lot more secure in many cases but for most people SMS should be perfectly suitable. All this of course requires the auth provider to be somewhat competent and not use SMS as an only factor in any circumstances.
FWIW I wouldn't regard SMS as a good 2nd authentication factor either, for the same reasons as this issue, it's too easy to get a carrier to transfer a number to an attacker.
Where it's used as a second factor, this still has an impact which is, if an attacker can get the password (and there's been enough breaches and keystroke logging for that to be common) they can then grab the number to get full control of the account.
TOTP or hardware tokens don't generally suffer from the same problem.
The problem is with most online services, the only second factor allowed is SMS.
If you see it as "don't bother, they can just steal your SMS number" instead of "that's slightly better, at least now they can't get in without stealing my number" then you're not thinking about this reasonably.
It's inane to neglect to use SMS where it's the only second factor available. The exception is when a service allows you to use SMS alone for password resets, which isn't MFA, is 1FA with a weaker factor than a password.
What would you think if someone took you for a joyride in a classic car and said "shoulder belts would be so much better than these lap-only belts, so don't bother buckling up!"
SMS is the only "second factor" that you can't control at all, your phone number can be changed from the phone company at any point, disabled, or suddenly refuse to work in a foreign country (all of those three happened to me).
For those reasons, even as a second factor it's a terrible one. SMS is just not a good method of authentication at all and has no place in a login form.
At it's best, SMS is only useful as a read-only notification system for non-sensitive purpose.
A bad second factor is better than no second factor.
I enabled TOTP on every account I have that supports it, which comes to about 2 out of every 5 services. I'm not going to leave the other 60% with only one factor just because SMS can be exploited, which the consensus in this thread seems to be advising everyone to do.
If someone can exploit your SMS, it's possible they can use that to social engineer their way into a password resets with services. (I forgot may password but I still have my phone.) So I would say a bad second factor can be strictly worse than no second factor.
You're describing single factor, not two factor. If you can change the password with SMS alone, it's not multi-factor. I plainly stated that exception two comments ago.
Except you have no way of knowing if that will be the case ahead of time. Unless the first thing you do after enabling 2FA is to social engineer a password reset for your account? Even then that doesn't guarantee that there isn't a more clueless service rep that will make a mistake.
Asking before you sign up, "will you allow my account to be hacked through social engineering?" isn't going to an answer other than no. Even if the answer is possibly yes.
But then let's please move the discussion from "Is SMS a good or bad second factor?" to "SMS is a mediocre second factor, and a terrible single factor. For this service, is it a second or single factor?"
You're incorrectly assuming that you can predict a site will never allow password reset via SMS only.
You can check if they appear to allow it today. Not perfectly, as they may have multiple variants and depending on other factors you might get presented with one or the other.
But you have no way to predict if next month a PM there decides their current password reset was too cumbersome and they change it to SMS-only. If you had a phone# on file, you're now suddenly vulnerable.
> TOTP or hardware tokens don't generally suffer from the same problem.
But how many hardware tokens or TOTP tokens are users willing to deal with? I currently have eight for various clients and systems at work. If each online account required a TOTP token or a custom hardware token it would be a confusing mess of tokens.
I don't know if there's a safe and easy way of reusing the same token across sites. Until then SMS really is the only "solution".
It is safe to use the same U2F token for many sites, that's not an issue. Having a backup token is very useful, but apart from that, a single hardware token (not custom - standards are good) can easily be used to secure all your accounts.
The only thing I wish is that more sites support multiple tokens, since tokens can get lost.
If you only support one token but have an easy recovery procedure, that opens up loopholes. If you support multiple tokens, allow the user to de-activate one token from another token, and make recovery difficult, that's much more secure.
Dropbox, Facebook, Google, GitHub, GitLab, even Login.gov works fine with multiple tokens.
More sites should do WebAuthn (you should not do greenfield deployments of U2F today, WebAuthn is the standard). Yes, AWS should fix their feature but that shouldn't block the next ten would-be Unicorns from doing WebAuthn.
But none of these support U2F or WebAuthn at all. The problem isn't that they need to support "multiple" tokens except in the sense that they don't support any at all.
It doesn't make sense to try to "support multiple keys" for TOTP. You can copy-paste TOTP seeds if that's what you want and feel comfortable with, if the site tries to allow you to use any of N seeds they not only increase their system complexity they also reduce their security by a factor of N which makes no sense.
Edited to add: OK, Coinbase does now have U2F and they clearly state you can use "a maximum of 5 keys" which feels like that's enough.
I've never seen a site that didn't have at least this.
Usually you get a UI where you can add new ones and remove old ones, and when you add a new one you name it in their UI so that you can tell it apart from any others.
Sure, no security measure is perfect. Hardware tokens are likely to have better properties than TOTP, which has better properties than SMS, which has better properties than nothing.
you can phish SMS exactly the same way you can phish TOTP, I'd say :)
It also comes with large downsides. Security is an economics game. Marginal improvements in security posture are not always worth the cost.
There are a bunch of people who insist that web services should drop SMS completely and demand that all users use TOTP (at least). I question the value of this change given that TOTP only protects you in comparatively rare cases.
This is certainly a vulnerability, but it also depends on how you get your TOTP codes. I use Bitwarden's browser extension to get mine, and if the domain is incorrect, the extension won't present me with the code. I think this is a decent level of protection from phishing.
I encourage you, as an exercise at least, to think about what you'll do when it doesn't work.
You're sure this is the right web site. But Bitwarden won't fill out the code. What could be wrong? Did the idiots who make this web site change the URL?
Now, maybe you're a far above average user and you would calmly determine the exact cause, assuming at every step that the most likely explanation is you're being phished. Hopefully that's more likely now that you've done this exercise. I would love to believe I'm in this category.
But most users will just be frustrated, why wasn't it filled out? Is there a way to get the code from Bitwarden anyway? There is, it's a bit fiddly but you can do it. Lots of users are going to do that. They might even help each other to give their credentials to bad guys, community spirit.
Hopefully some of those users pause because this is unusual and a few of them will realise in that moment that they're being phished. But experiments suggest most won't.
I did consider this, and I would also like to believe that my first thought would be "I am being phished" rather than "I'm sure this is the right web site." I do understand that many users (including myself on a bad day) might not recognize a phishing situation. But at least there is a layer of defense that SMS doesn't have.
Maybe the Bitwarden extension should warn users when they try to copy/view a TOTP code by searching for a login rather than using a matched entry.
U2F is my preferred method of MFA, but many services don't support it, and there can be practical issues even for the ones that do. For example, some services support U2F in a browser but not in mobile apps.
The point is the TOTP is precisely as bad as SMS for the common case (phishing) and only safer in a rare case (SIM-swap). This comes with large downsides (losing access).
TOTP is, at best, a very marginal improvement over SMS. This is what makes the online push to complain about services that use SMS 2FA and demand a switch to TOTP very strange.
TOTP is far, far better for travellers who need to swap their SIM cards frequently, or need to work out of places with internet access but no cell reception.
SMS is not a good second factor, even as a second factor.
I deprecated SMS 10 years ago and the only way I receive SMS codes is via an online interface that is password access.
For most people, SMS fails miserably when you need to change your SIM card or fly to another country, or work out of a place with no cell reception but has wired or wi-fi internet access. That's a big part of the reason why I deprecated it in favor of e-mail, which works flawlessly anywhere in the world you have an internet connection.
I only support U2F or TOTP based 2FA and it's upto providers to get with the beat if they want me to use real 2FA.
Exactly this. Here in Israel, SMS is used extensively as part of a multi-factor authentication system. I also require my National ID.
To move my phone number (consent or not) between any phone companies requires an SMS, my National ID, and verification of my ID, and personal details in the government database.
The option for a delay of is great. The option of adding a custom security question/password etc. is even better. The option of completely turning off recovery is also great. The ability to have your solution on multiple devices without a need for a mobile phone number based recovery is great as well.
I hate it that Twitter forces you to enter a mobile phone number even when you set up an authenticator code generator as 2FA.
Oftentimes the weakest link in most of these services is the account recovery part.
When we set up the self service account recovery in saas pass password manager and authenticator we added all of these customizable options to mitigate against potential SIM Swap attacks.
On Twitter you can remove your phone number after the fact tho. In fact most sites that req a phone number to sign up etc allow you to remove the phone number later if you choose.
> The very things that make SMS a uniquely good second factor make it an awful only factor. Use of SMS for account recovery should in general (or at least for important accounts) have a delay (order of days) that allows the real user to intervene.
No, SMS shouldn't be a single factor, period. It doesn't prove much, and is insecure, as the current post shows.
SMS will remain vulnerable as long as the mobile accounts that hold them upstream remain vulnerable.
One option I’ve heard might be different is to not your your mobile sms on accounts, but to get a voip based sms number. It might leave things at the mercy of a different system but the footprint might be different.
I've tried this, but many companies block VoIP numbers for MFA/2FA. Some don't. This works with LinkedIn, but not any companies I have purchased things from.
It's a little mind boggling though. Securing money with a $15/mo phone plan. It's an extremely ghetto phone service. If anyone's to blame, it's Boost Mobile. Cricket Wireless. Pay for a major carrier plan.
The very things that make SMS a uniquely good second factor make it an awful only factor. Use of SMS for account recovery should in general (or at least for important accounts) have a delay (order of days) that allows the real user to intervene.