Xavier's diary entry "(Ab)Using Security Tools & Controls for the Bad" on PAM, reminded me of a script to backdoor pam_unix.so: linux-pam-backdoor.

This script will download the PAM source code, patch it to add an hardcoded skeleton key password, and compile it.

There's also a script to detect backdoored pam_unix.so files like this: linux-pam-backdoor-detect.sh

This scripts looks if there is an extra string between the following strings:

Didier Stevens
Senior handler
Microsoft MVP
blog.DidierStevens.com