PyPAM is a PAM binding for Python.
PyPAM does not handle passwords correctly if there is NULL byte in the string.
A remote attacker could possibly execute arbitrary code or cause a Denial of Service condition.
There is no known workaround at this time.
All PyPAM users should upgrade to the latest version:
# emerge --sync
# emerge --ask --oneshot --verbose ">=dev-python/pypam-0.5.0-r3"