openssh unix dev - Jul 2005 - Pam module leaks information

Hello All,

Im using OpenSSH 4.1 with a proprietary pam module. This module does allow
or deny access to the accound based on a policy file settings. Now if I deny
the access to an account and attempt to connect to the sshd server for that
account with valid password, it quickly returns to next prompt. When I try
it with invalid password, it took some time to return to next prompt. Im
wondering if this kind of behaviour will lead to information leak on
password validity. Should I need to contact the author of this module to
compensate the difference in timing factor.

Thanks,
Senthil Kumar.

Senthil Kumar wrote:
> Im using OpenSSH 4.1 with a proprietary pam module. This module does allow
> or deny access to the accound based on a policy file settings. Now if I
deny
> the access to an account and attempt to connect to the sshd server for that
> account with valid password, it quickly returns to next prompt. When I try
> it with invalid password, it took some time to return to next prompt. Im
> wondering if this kind of behaviour will lead to information leak on
> password validity. Should I need to contact the author of this module to
> compensate the difference in timing factor.
I'm not aware of any remaining timing info leaks in the PAM code in 
OpenSSH 4.1p1 (we spent some time a while back stomping them out) but if 
there are any left then they ought to be found and fixed.

That said, it sounds like your module is the source of the timing 
discrepancy.  Does it behave the same way with other PAM apps?

What platform is this?  On Linux, you may have to explicitly set 
pam_fail_delay (eg with this module: 
http://www.zip.com.au/~dtucker/patches/#pam_faildelay).

-- 
Darren Tucker (dtucker at zip.com.au)
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     Good judgement comes with experience. Unfortunately, the experience
usually comes from bad judgement.