No; every implementation fails in some new and creative way.
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 commented on the other thread, but will repeat here: I really like how Django handles password resets.
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.
If you want to get clever to avoid touching the database --- which is why every broken password reset feature ever conceived decided to get clever --- you should have your code assessed professionally. I'm not telling you it's impossible to build a secure password reset that doesn't simply store a token in the database. I'm just saying the cost/benefit payoff is probably not there.
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.
The good thing about taking your web stack's password reset feature, if it has one, is that you're probably going to find out quickly if there's a bug discovered in it.
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 added a timeout period to the password reset in Django 1.2, it defaults to 3 days, the only issue I'm aware of is that it calculates the timeout in days which isn't very convenient if you want to be extra-careful.
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 django-password-reset app appears to be pretty much equivalent to the django.contrib.auth.views version, except, as you say, with CBVs and perhaps some extra customisability in the templates and user lookup methods.
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.
It appears better than most [of the non-DB] implementations I've seen, and as huxley mentions downthread, newer releases do have settings.PASSWORD_RESET_TIMEOUT_DAYS which defaults to 3 to deal with timeouts.
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.
If you have to use any cryptography other than "generate random number" to implement password reset, you should be ready to cough up $7-14k for a professional security assessment.
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.
With respect to (a), for the applications that require some level of admin function, I say to not allow password reset for those higher-level priv accounts.
The difference is that as soon as the token is used, even unsuccessfully, it is whacked from the database. Whether or not password reset is actually completed.
No, this is unnecessary. An attacker who can pull tokens out of the database already has a terrible vulnerability and can probably avoid the need for passwords altogether.
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.
> [...] and can probably avoid the need for passwords altogether.
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.
I have never, ever, ever, ever seen an application one-way hash their reset tokens to prevent disclosure of them from their database. That's all I'm going to say here.
What I'll argue is that it's not a best practice, because nobody practices it. I also think it's a silly countermeasure, but I don't feel like I need to defend that 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. :)
> What I'll argue is that it's not a best practice, because nobody practices it.
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.
