[shadowgovt]

I think this argument falls flat on two axes:

- in general, if the system is broken enough to be giving false-negatives on valid credentials, it's broken enough that there isn't much planning to be done here because the system's not supposed to break. So if they give me "Sorry, backend offline" instead of "invalid credential," they've now turned their system into an oracle for scanning it for queries-of-death. That's useful for an attacker.

- in the specifics of this situation, (a) credential reset was offline too so nobody could immediately rotate them anyway and (b) as a cohort, Facebook users could stand to rotate their credentials more often than the "never" that they tend to rotate them, so if this outage shook their faith enough that they changed their passwords after system health was restored... Good? I think "accidentally making everyone wonder if their Facebook password is secure enough" was a net-positive side-effect of this outage.

[shkkmo]

So your approach to security is to never admit that an application had an error to a user, but to instead gaslight that user with incorrect error messages that blame them?

This is security by obscurity of the worst kind, the kind that actively harms users and makes software worse.

[shadowgovt]

No. My approach to security is to never admit that an application had an error to an unauthenticated user.

That information is accessible to two cohorts:

- authenticated users (sometimes; not even authenticated users get access to errors as low-level as "The app's BigTable quota was exceeded because the developers fucked up" if it's closed source cloud software)

- admins, who have an audit log somewhere of actual system errors, monitoring on system health, etc.

Unfortunately, I can't tell if the third cohort (unauthenticated users) is my customers or actively-hostile parties trying to make the operation of my system worse for my customers, so my best course of action is to refrain from providing them information they can use to hurt my customers. That means, among other things, I 403 their requests to missing resources instead of 404ing them, I intentionally obfuscate the amount of time it takes to process their credentials so they can't use timing attacks to guess whether they're on the right track, I never tell them if I couldn't auth them because I don't recognize their email address (because now I've given them an oracle to find the email addresses of customers), and if my auth engine flounders I give them the same answer as if their credentials were bad (and I fix it fast, because that's impacting my real users too).

To be clear: I say all this as a UX guy who hates all this. UX on auth systems is the worst and a constant foil to system usability. But I understand why.