(RHSA-2010:0258) Low: pam_krb5 security and bug fix update

The pam_krb5 module allows Pluggable Authentication Modules (PAM) aware
applications to use Kerberos to verify user identities by obtaining user
credentials at log in time.

A flaw was found in pam_krb5. In some non-default configurations
(specifically, those where pam_krb5 would be the first module to prompt for
a password), the text of the password prompt varied based on whether or not
the username provided was a username known to the system. A remote attacker
could use this flaw to recognize valid usernames, which would aid a
dictionary-based password guess attack. (CVE-2009-1384)

This update also fixes the following bugs:

• certain applications which do not properly implement PAM conversations
  may fail to authenticate users whose passwords have expired and must be
  changed, or may succeed without forcing the user’s password to be changed.
  This bug is triggered by a previously-applied fix to pam_krb5 which makes
  it comply more closely to PAM specifications. If an application misbehaves,
  enabling the “chpw_prompt” option for its service should restore the old
  behavior. (BZ#509092)

• pam_krb5 does not allow the user to change an expired password in cases
  where the Key Distribution Center (KDC) is configured to refuse attempts to
  obtain forwardable password-changing credentials. This update fixes this
  issue. (BZ#489015)

• failure to verify TGT because of wrong keytab handling. (BZ#450776)

Users of pam_krb5 are advised to upgrade to these updated packages, which
resolve these issues.