Re: OpenSSH/PAM timing attack allows remote users identification

[Marco Ivaldi <raptor () mediaservice net>]

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@host
> root@host's password: <- arbitrary (non-null) string
> [2 secs delay]
> Permission denied, please try again.a
>
> $ ssh root@host
> root@host'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/