PAM_KRB5(8) | System Manager's Manual | PAM_KRB5(8) |
pam_krb5
—
Kerberos 5 PAM module
[service-name] module-type control-flag pam_krb5 [arguments]
The Kerberos 5 service module for PAM provides functionality for three PAM categories: authentication, account management, and password management. It also provides null functions for session management.
The Kerberos 5 authentication component provides functions to
verify the identity of a user
(pam_sm_authenticate
())
and to set user specific credentials
(pam_sm_setcred
()).
pam_sm_authenticate
() converts the supplied username
into a Kerberos principal, by appending the default local realm name. It
also supports usernames with explicit realm names. If a realm name is
supplied, then upon a successful return, it changes the username by mapping
the principal name into a local username (calling
krb5_aname_to_localname
()).
This typically just means the realm name is stripped.
It prompts the user for a password and obtains a new Kerberos TGT for the principal. The TGT is verified by obtaining a service ticket for the local host.
When prompting for the current password, the authentication module
will use the prompt “Password for
<principal>:
”.
The
pam_sm_setcred
()
function stores the newly acquired credentials in a credentials cache, and
sets the environment variable KRB5CCNAME
appropriately. The credentials cache should be destroyed by the user at
logout with kdestroy(1).
The following options may be passed to the authentication module:
debug
LOG_DEBUG
level.no_warn
use_first_pass
try_first_pass
use_first_pass
option, except that if the previously obtained password fails, the user is
prompted for another password.renewable
=timeperiodforwardable
no_ccache
ccache
=name%u
’, to designate the
decimal UID of the user; and ‘%p
’,
to designate the current process ID; can be used in
name.allow_kdc_spoof
pam_krb5
to succeed even if there is no host
or service key available in a keytab to authenticate the Kerberos KDC's
ticket. If there is no such key, for example on a host with no keytabs,
pam_krb5
will fail immediately without prompting
the user.
Warning:
If the host has not been configured with a keytab from the KDC, setting
this option makes it vulnerable to malicious KDCs, e.g. via DNS
flooding, because pam_krb5
has no way to
distinguish the legitimate KDC from a spoofed KDC.
The Kerberos 5 account management component provides a function to
perform account management,
pam_sm_acct_mgmt
().
The function verifies that the authenticated principal is allowed to login
to the local user account by calling
krb5_kuserok
()
(which checks the user's .k5login file).
The Kerberos 5 password management component provides a function
to change passwords
(pam_sm_chauthtok
()).
The username supplied (the user running the
passwd(1) command, or the
username given as an argument) is mapped into a Kerberos principal name,
using the same technique as in the authentication module. Note that if a
realm name was explicitly supplied during authentication, but not during a
password change, the mapping done by the password management module may not
result in the same principal as was used for authentication.
Unlike when changing a UNIX password, the password management module will allow any user to change any principal's password (if the user knows the principal's old password, of course). Also unlike UNIX, root is always prompted for the principal's old password.
The password management module uses the same heuristics as kpasswd(1) to determine how to contact the Kerberos password server.
The following options may be passed to the password management module:
debug
LOG_DEBUG
level.use_first_pass
try_first_pass
use_first_pass
option, except that if the previously obtained old or new passwords fail,
the user is prompted for them.The Kerberos 5 session management component provides functions to
initiate
(pam_sm_open_session
())
and terminate
(pam_sm_close_session
())
sessions. Since session management is not defined under Kerberos 5, both of
these functions simply return success. They are provided only because of the
naming conventions for PAM modules.
KRB5CCNAME
Applications should not call
pam_authenticate
()
more than once between calls to
pam_start
()
and
pam_end
()
when using the Kerberos 5 PAM module.
The pam_krb5
module implements what is
fundamentally a password authentication scheme. It does not use a Kerberos 5
exchange between client and server, but rather authenticates the password
provided by the client against the Kerberos KDC. Therefore, care should be
taken to only use this module over a secure session (secure TTY, encrypted
session, etc.), otherwise the user's Kerberos 5 password could be
compromised.
March 10, 2007 | NetBSD 10.99 |