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Yahoo discloses hack of 1B accounts

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Re: Yahoo discloses hack of 1B accounts

#461

Post by patates »

dogma1138 wrote: post #318
drodgers wrote: post #315

Earlier quoted context omitted.

If the password is stored properly, (i.e. bcrypt) then there does need to be some length limit or it becomes too easy to DoS a service by sending it hundreds of megabytes of password to bcrypt. There's no reason for that length limit to be less than 100 characters though.

You are going to be limited by the max http request size way before that. To upload 100s or even more than a few megs you need a multipart message, a password form won't accept MP http requests.

On the back-end there usually is a naive POST handler which happily accepts anything it can parse, unless a mature framework with sane defaults is used.

Re: Yahoo discloses hack of 1B accounts

#462

Post by jondubois »

I'm using Yahoo mail and when I logged in, they gave me a link to their security notice. About 'Hashed passwords', it says:

"At the time of the August 2013 incident, we used MD5 to hash passwords. We began upgrading our password protection to bcrypt in the summer of 2013. Bcrypt is a password hashing mechanism that incorporates security features, including salting and multiple rounds of computation, to provide advanced protection against password cracking."

WOW. So basically they did not even salt their passwords until 3 years ago! I knew about the importance of salting password hashes since I was like 17 years old and this mega billion-dollar corporation did not.

Also, they claim:

"Hashing is a one-way mathematical function that converts an original string of data into a seemingly random string of characters. As such, passwords that have been hashed can’t be reversed into the original plain text password."

Which in the case of MD5 is a deceptive claim; even a basic dictionary attack could probably reverse at least 50% of all their accounts' MD5-hashed password (assuming most people use one-word passwords with maybe a few digits at the end).

Re: Yahoo discloses hack of 1B accounts

#463

Post by kreetx »

geofft wrote: post #242
JonDav wrote: post #136

Earlier quoted context omitted.

I thought the whole point of the MD5 vulnerability was that the limit was 2^128 and as such there are more inputs that possible output hashes, meaning more possible input collisions.

Every hash has a finite output length, and therefore a finite number of possible outputs. 2^128 is a very large finite number. It's not that large in the grand scheme of things (there are over 2^260 or so atoms in the universe), and it's definitely better to use a hash with 2^256 outputs now that there exist good 256-bit hashes that are faster than MD5, but 2^128 is still quite a large number. The internets are quoti…

This is a very clear explanation, thanks!

Re: Yahoo discloses hack of 1B accounts

#464

Post by d33 »

jondubois wrote: post #462

I'm using Yahoo mail and when I logged in, they gave me a link to their security notice. About 'Hashed passwords', it says: "At the time of the August 2013 incident, we used MD5 to hash passwords. We began upgrading our password protection to bcrypt in the summer of 2013. Bcrypt is a password hashing mechanism that incorporates security features, including salting and multiple rounds of computation, to provide advanc…

It's one thing to know it and the other to deploy it. You don't know how messed up their system might be - it might actually be a very difficult change if it's tied to other components with some crazy kludges. Looks like they didn't prioritize them well enough. And if you're looking for an example of a company that's way too afraid of changing anything in their system because it's too much of a mess, consider PayPal an example...

Re: Yahoo discloses hack of 1B accounts

#465

Post by chrischen »

duaneb wrote: post #203
Arubis wrote: post #165

Fittingly, attempting to change my password to a 32-character random string generated by 1Password returns an error that the password "cannot contain my email or username", regardless of the contents of that random string (I tried several). It does, however, _happily_ accept `passwordpassword` and cheerily move along to confirming that my recovery email account from 2003 is still valid.

Gonna guess that's a bad message for a password length violation or something else. Not that it's much better. Is it so hard to allow 50 character passwords?

It's probably a naive substring detection check.

Re: Yahoo discloses hack of 1B accounts

#466

Post by blowski »

kijin wrote: post #418
dlubarov wrote: post #347

Earlier quoted context omitted.

I think it's best to allow longer passwords for those who use long phrases. It's easier to remember the full phrase than a truncated version. You could show a warning that the extra chars beyond 50-55 will be ignored.

Or you could SHA256 the original password and feed the hash to bcrypt. Remember to use the 64-byte hexadecimal hash, not the 32-byte binary because bcrypt chokes on null bytes. Everyone's been saying "just use bcrypt", but bcrypt has too many gotchas to be the default choice. We really need to work on getting scrypt and argon2 into the most popular programming languages and frameworks a.s.a.p.

> Everyone's been saying "just use bcrypt", but bcrypt has too many gotchas to be the default choice

This has got to be the underlying problem of modern security. By the time a best practice is well known, it's no longer best practice.

Re: Yahoo discloses hack of 1B accounts

#467

Post by ProbabilityMoon »

kstrauser wrote: post #430

DO NOT delete your Yahoo account! In their disclaimer when you delete it, they state: > "[...] we may allow other users to sign up for and use your current Yahoo! ID and profile names after your account has been deleted" Bummer if you forget that it was the password reset email for your Facebook account, huh? Instead of deleting your account, purge it of all data: https://honeypot.net/purge-your-yahoo-account/

I just deleted all data from my account and set an automatic responder stating that, due to security concerns, I no longer use that account. I created my Y! account in 1998, it's a shame it has come to this. There were a lot of memories I had to purge along with my account (even though I had a different main account in the last decade). Shame!

Re: Yahoo discloses hack of 1B accounts

#468

Post by mike_hearn »

alyandon wrote: post #275
dsl wrote: post #197

Earlier quoted context omitted.

The forged cookie attack was used on a limited number of accounts, by a state sponsored actor. Going to this amount of effort and then sending spam would be on par with breaking into a bank just to steal the printer paper from the office. Most likely either: 1) you were phished and didn't realize it 2) logged in to your Yahoo account from a device that had malware on it

I'm willing to accept that perhaps that was not how my account was compromised but the time frame when this happened was well in line for when this breach supposedly occurred. Regardless, it was some sort of automated spam/phishing emails that were sent from Yahoo's network using my account to contacts on my list. I analyzed the headers of multiple bounced messages that were sent to email addresses no longer in use a…

You reused the password on other websites, I'm guessing. Especially likely if it was a strong (i.e. hard to memorise) password.

The bulk hacking attacks that began around Spring 2010 hit all the big webmail providers. The source of the passwords was always, without fail, reversed hashes from breakins at other big websites:

https://googleblog.blogspot.ch/2013/02/an-update-on-our-war-...

Source: was a tech lead on the Google anti-hijacking team during this period.

Re: Yahoo discloses hack of 1B accounts

#469

Post by _pdp_ »

phantom_oracle wrote: post #89

there's a couple of things that these major providers getting pwned teaches you: 1) their security isn't good just because of their scale/size (that begins to seem more and more like a false-assumption nowadays) 2) migrating your email to a new provider is quite difficult (consider that the average person will have just 1 - or 2 - email accounts and they link EVERYTHING to it) 3) the price of ads/convenience is no lo…

Just use your own domain. That gives you the ultimate power over the your emails regardless of the mail provider you end up using.

Re: Yahoo discloses hack of 1B accounts

#470

Post by zeveb »

dlubarov wrote: post #347
sk5t wrote: post #319

Earlier quoted context omitted.

It sort of does matter for bcrypt, surprisingly: http://security.stackexchange.com/questions/39849/does-bcryp... In the interests of hewing closest to cryptographic reality, I design not to allow a password longer than the algorithm can usefully use.

I think it's best to allow longer passwords for those who use long phrases. It's easier to remember the full phrase than a truncated version. You could show a warning that the extra chars beyond 50-55 will be ignored.

> You could show a warning that the extra chars beyond 50-55 will be ignored.

Or you could use a better KDF, e.g. scrypt (even PBKDF2 is better on this metric). Artificial password-length restrictions are symptomatic of poor design.

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