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Re: Including pam_faildelay module in PAM distribution/possible security problem



On Sun, Oct 22, Bjoern Voigt wrote:

> Hello!
> 
> Since long time I miss support for PAM's pam_fail_delay() function in 
> common Linux applications. For instance, OpenSSH and SUDO don't support 
> fail delay without special patches.

Something I should mention here: pam_fail_delay() has a huge drawback/
security problem:

Since libpam is sleeping here, the application has no chance to log
the failed authentication attemp.

Depending on the application, you can abort the application with
Ctrl-C while it is inside of the delay function. As result, there
will never be a syslog entry about the failed login attemp.

We had some time (years?) ago the security problem that attacker 
could use some applications for brute force attacks by aborting 
them during the delay, because the following happend:

- authentication fails
- sleep()
- syslog()

This was changed to
- authentication fails
- syslog ()
- sleep ()


With pam_fail_delay, you will always have sleep before syslog, this is
not changeable.

And I have no good idea how to make sure that the libpam sleep will
not be aborted.

  Thorsten

-- 
Thorsten Kukuk         http://www.suse.de/~kukuk/      kukuk suse de
SUSE LINUX Products GmbH       Maxfeldstr. 5       D-90409 Nuernberg
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