Password Hijacking Security Incident and Response
blog.heroku.com
blog.heroku.com
The implementation I feel most comfortable with:
1. Generate a 256+ bit cryptographically secure random number and base64 it to create a token.
2. Record that token in your database, timestamped, along with the user account for which the token was requested.
3. Mail the token to the user's email address.
4. When the user returns to the site after recovering the token, use that token to look up their account from the database.
5. Expire tokens within single-digit hours so users don't end up accidentally banking password-equivalents in their email accounts.
6. When a user changes their password or requests another password reset, expire all tokens already associated with their account.
I would also recommend:
(a) Not having any in-band administration functionality in your application; instead, have a separate admin application, attached to the same databases, available only on a VPN.
(b) Require 2-factor authentication (such as Duo Security) for both admin VPN access and admin login.
A knock-on benefit of (a): your admin functionality is easier to build, because it doesn't have to do the UI/UX chinups your normal exposed app code has to do; crappy looking admin screens nobody but your employees see are generally fine.
I'm not trying to drum up business. I would strongly prefer that you not try to be clever with this feature. Or, you can ignore the audit and just be the subject of a blog post like this sometime in the future.
No nonce is generated and nothing is stored. The user is emailed a link with her user ID and a token that's a hash of (last login timestamp + the user's ID + the user's (hashed) password + current timestamp). The token is HMAC-signed with the site's secret key.
This way the token automatically expires if the user either successfully changes her password (the password hash will change) or manages to log in (last login timestamp changes).
It seems that in Django password reset tokens are valid forever, but it would be trivial to add the current timestamp to the token and include it when computing the HMAC signature; then the password reset form would check if the token has been generated recently enough.
I like this method because you never need to touch the database and store tokens; it's all fairly stateless.
Personally, I have this particular bit of appsec down cold, and if I was building a new app, I wouldn't even think about it: I'd use a random token and save it in the database.
I wouldn't roll my own password reset feature if I can just take the builtin one from Django, which is what I did.
Note though that that's not the case for 3rd-party password reset libraries or, more likely, the all-purpose security library that provides it. I'd be very wary about using a 3rd party library for password reset unless they've got a credible for story for it having been reviewed.
Django: Good.
3rd Party Library: Less Good
Just Using A Random Token: Good
Cryptography: You Will Perish In Flames
Asking this since it's probably the most widely used authentication gem in Rails etc...
https://docs.djangoproject.com/en/1.4/ref/settings/#std:sett...
Haven't looked too closely at it but Bruno Renié has a Django app that has done most of the heavy-lifting to make password reset customizable by providing as class-based views and changing the timeout period granularity to seconds (it defaults to 172800 seconds or 2 days):
The main criticism of both this and the contrib.auth are that they use the (hashed) user info directly, rather than generating a random code and associating it with the user in a lookup table.
This app actually appears (on my brief inspection) to be less secure than the django.contrib.auth one, since it is using the django.core.signing.loads/dumps methods with a simple static salt, whilst the contrib.auth uses django.contrib.auth.tokens.PasswordResetTokenGenerator which includes a bunch more state in the token, so that it's auto-invalidated if the user subsequently logs in, changes their password, or other things).
Personally, I wouldn't recommend it.
I'm torn between the "standard" contrib.auth implementation, and the basic {random token, user, expiry} model espoused by tptacek and others throughout this thread.
I am curious as to why the Django devs implemented this the way they did though, given the significant added complexity.
Additionally, this token could be valid for a very long time.
I would probably flag this approach in an assessment.
It doesn't handle point 6 of tptacek's list though; that subsequent tokens should invalidate all those prior. You could do that by adding an incrementing 'password_resets' or 'last_reset_issued_at' field to the User model, and including that in the token generator state, but it feels a bit clunky.
I'm not sure why people are placing such an emphasis on DB avoidance; it seems to me that password-reset activities should be a relatively minor source of load for your application in virtually all circumstances.
The token is a password equivalent, and should thus not be stored in clear (use scrypt or a similar scheme).
I've tested many many many many applications in the last X years and not one of them has ever done this, nor would I ever recommend that they do it.
Probably, yeah...
In the case they only have read access to the token DB, and need write access, or read access to another part of the system, it becomes an attack vector.
It is not a cargo-cult measure, and it doesn't add much complexity (just re-use your password encoding logic).
The same goes for session tokens, BTW.
> [...] nor would I ever recommend that they do it.
Maybe you should reconsider that. I know who you are, and how knowledgeable and experienced you are, but in this case I think you're just wrong.
A cargo cult is not an argument.
I would not hash reset tokens, but I didn't downmod you for suggesting it. I would get mad at you if you worked on my team and dinged a client for not doing it, though. :)
And now you're begging the question!
Actually, some people use it :-).
It shuts down an attack vector, and it's cheap to implement. Why is it silly? My rule of thumb is to treat all passwords equivalents in the same way.
I'm honestly surprised by your hostility towards the idea (not mine, BTW), and by the downvotes for promoting a strategy that provably (in the math sense) increases security.
http://stackoverflow.com/questions/549/the-definitive-guide-...
Edit: Even if it were just me, it doesn't make the argument invalid.
Your arguments so far are
1) it's unlikely to be the weakest link. Textbook case of Murphy's law,
2) nobody does it, and
3) I've never recommended it, therefore it's useless.
I don't understand how you can resort to that... Seriously, I'm at loss here. Are you waiting for a high profile attack to react?
I know you have a reputation to defend, but I think you screwed it somehow in this case.
At least, it proves you're not a machine :-)
:)
Edit: random Divine Comedy song: http://www.youtube.com/watch?v=EN65hsrtg94
And with 6, i suggest expire at step 4.
(I thought about it and decided to just have one expiry instruction).
2. Email
3. Thick clients.
4. File upload.
5. File download.
6. Templating (as an app feature, not as a dev tool).
7. "Advanced Search".
This list is a couple years old. We're going to start tying bug reports to functional areas in targets to get a better empirical list by the end of the year. I expect the new empirical list to be more boring and less useful, though.
1. Breaks out of the web security domain, requiring devs to think through and implement controls that compensate for things like sessions and access control.
2. New quoting domain creates opportunities for injection to leverage apps to send unexpected messages.
3. Often involves shelling out, with all the attendant risks of that.
4. Inbound mail has different input restrictions than web apps do, creating opportunities for submarined XSS or even SQLI.
It's just a really common place where apps suddenly sprout unexpected moving parts, is what it boils down to.
This way there is no risk of someone somehow guessing the reset link. Even if they do, all it does is email the user, so they gain nothing...
Don't do it this way.
Then the system FORCES them to change the password when they login with the new password.
Oh - and the tempoary password only valid for 24 hours.
So you get the best of both worlds - without anyone being able to 'guess' anything able to do anything...
I'm sure there's a million fiddly things you can do to address the weaknesses of temporary password issuance, but you'd be better off sending a semantically meaningless random token. All the countermeasures you're thinking of here apply identically to the token.
I am advocating for the reset scheme that is the hardest to mess up. Yours is not the hardest to mess up. I'm not trying to get you to change yours.
- User enters email address to reset password
- A reset link (uniquely hashed,salted etc.) is generated server side tied to that specific email address. This link can only be used once and also has a expiry date if un-used by that time.
- If this reset link is accessed (hopefully by the intended user), A form is presented to the user where it asks to enter the email address, new password. If entered email address does not match the original email, user gets an error. Immediately, all sessions are invalidated/reset if any. If entered email address matches, then reset the user's password. Again, invalidate/reset any existing sessions.
- After resetting password, never login the user directly. Ask them to login manually again.
What vulnerability could this close? In order to finish the reset procedure in the previous step, any attacker would need to know the user's email address, and the attacker would obviously know the new password that was just set. I'm probably missing something, but I don't see this extra step adding any security.
For example: A user with a valid session cookie for one account, follows a password reset link for some other account. Or a user generates a password reset link, logs in with an old password, changes the password and follows the reset link.
There are many such tricky cases and the challenge is to explicitly design how they should be handled and cover them with tests.
"What? Every page gets 'current user' from a common header included in every file that it pulls out of the session, and this page also takes 'email address' from a parameter passed in by the user? OOPS."
So just use the token.
So you are a strong advocate of generating the token and storing it in the db.
This is interesting.
I would have liked to see more details about what was going on to cause that sort of problem. I can't think of any reasonable code that would cause password resets for an empty ID to be assigned to a random account.
#Start a password reset
@user = User.find_by_email
@user.update_attribute :password_reset_nonce, rand(16 ** 16).to_hex
#mail them the password reset email
#Look up a user for a password reset
@user.find_by_password_reset_nonce params[:password_reset_nonce]
#if nil, above line returns random user on some databases. Oops.
session[:user_id] = @user #Logs in user
#We assume if they know the nonce that proves they own email.
redirect_to passwordReset_url
Bugs like this one always make me think "There but for the grace of God go I."
rand(16**16).to_s(16)
rand(16**16).to_s(36)