cron+pam heavily spamming my logs

Javier gave a Debian specific answer there: http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=293272#36

I added this at the beginning of /etc/pam.d/cron on a Lenny system and it worked (I restarted cron but I don't know if that was necessary):

session     [success=1 default=ignore] pam_succeed_if.so service in cron quiet use_uid

This is the relevant portion of /etc/pam.d/password-auth on a Fedora system with a silent crond:

session     optional      pam_keyinit.so revoke
session     required      pam_limits.so
session     [success=1 default=ignore] pam_succeed_if.so service in crond quiet use_uid
session     required      pam_unix.so

The important line is the third one. Put that in the appropriate location in Debian's PAM config and that should shut it up.