bugtraq - Re: OpenSSH/PAM timing attack allows remote users identification

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Date: Mon, 5 May 2003 14:55:51 +0200 (CEST)
From: Marco Ivaldi <raptor@...iaservice.net>
To: Ethan Benson <erbenson@...ska.net>
Subject: Re: OpenSSH/PAM timing attack allows remote users identification


On Thu, 1 May 2003, Ethan Benson wrote:

> ive noticed something similar in its handling of PermitRootLogin, if
> this option is set to `no' you get the following behavior:
>
> $ ssh root@...t
> root@...t's password: <- arbitrary (non-null) string
> [2 secs delay]
> Permission denied, please try again.a
>
> $ ssh root@...t
> root@...t's password:  <- correct root password
> [no delay]
> Permission denied, please try again.
>
> i haven't checked the current version to see if this is still true.

It is, also in the latest OpenSSH_3.6.1p2. I'm not sure if this behaviour
has serios security implications, however it can be "fixed" applying the
same workaround suggested for CAN-2003-0190: use the "nodelay" option for
pam_unix.so.

--
Marco Ivaldi
Chief Security Officer    Data Security Division
@ Mediaservice.net Srl    http://mediaservice.net/