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Re: gdm Create User



Steve Grubb wrote:
On Sunday 07 October 2007 11:33:45 Lubomir Kundrak wrote:
A successful account breach requires 3 things: a machine name, a valid
account, and the password. Letting people know that an account is valid
cuts the attack down to a dictionary attack.
So what about trying to hide the machine name?

Yes that is a good thing to try, but likely to be exposed. NAT's do some degree of protecting this. But this is really not the point of this thread.

This is plain nonsense. Time that was spent avoiding timing `attacks' was
wasted. The _password_  is meant to be a key that is to be hidden, not the
account name.

No, it is both. This is why face logins are bad in a secure setting.

Since I seem to have helped start this thread with some random comments off of my head, including the mistaken assumption that gdm reports 'invalid username', I'll just say here-

+1 to face logins _providing_ usernames, as opposed to this whole debate about 'invalid username' leaking _non-usernames_. I.e, if people actually wanted to implement something like I suggested, i.e. unknown username spawning create-user process, then the disabling of the feature for security reasons should be advertised right next to the disablement of the face-login feature, for the same reasons.

Again, it all boils down to threat models, and the balance of convenience with respect to providing the most benefit for what is targeted as the default installation. Thus the question is, for the default installation, does the increased vulnerability outweigh the increased convenience. Clearly if face-login is enabled by default, it seems like this leakage of non-usernames is not a serious increase in vulnerability, as long as it is obvious to disable it at the same time and for the same reasons as disabling the face-login feature.

$0.02...

-dmc

"For me, given my threat model and how much my time is worth, life is too short for SELinux."


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