Red Hat Security Advisory 2015-1640-01 - Pluggable Authentication Modules provide a system whereby administrators can set up authentication policies without having to recompile programs to handle authentication. It was discovered that the _unix_run_helper_binary() function of PAM's unix_pam module could write to a blocking pipe, possibly causing the function to become unresponsive. An attacker able to supply large passwords to the unix_pam module could use this flaw to enumerate valid user accounts, or cause a denial of service on the system.
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