---
advisories:
- date: 2009-02-11
  threshold: '3.13'
  versions: 3.12 and earlier
blurb: |
  pam-krb5 is a Kerberos PAM module for either MIT Kerberos or Heimdal.  It
  supports ticket refreshing by screen savers, configurable authorization
  handling, authentication of non-local accounts for network services,
  password changing, and password expiration, as well as all the standard
  expected PAM features.  It works correctly with OpenSSH, even with
  ChallengeResponseAuthentication and PrivilegeSeparation enabled, and
  supports extensive configuration either by PAM options or in krb5.conf or
  both.  PKINIT is supported with recent versions of both MIT Kerberos and
  Heimdal and FAST is supported with recent MIT Kerberos.
build:
  autoconf: '2.64'
  automake: '1.11'
  autotools: true
  kerberos: true
  manpages: true
  middle: |
    The module will be installed in `/usr/local/lib/security` by default,
    except on 64-bit versions of Linux which will use
    `/usr/local/lib64/security` to match the default PAM configuration.  You
    can change the installation locations with the `--prefix`, `--mandir`, and
    `--libdir` options to configure.  The module will always be installed in a
    subdirectory named `security` under the specified libdir.  On Linux, use
    `--prefix=/usr` to install the man page into `/usr/share/man` and the PAM
    module in `/lib/security` or `/lib64/security`.
  reduced_depends: true
  type: Autoconf
copyrights:
- holder: Russ Allbery <eagle@eyrie.org>
  years: 2005-2010, 2014-2015, 2017
- holder: The Board of Trustees of the Leland Stanford Junior University
  years: 2009-2011
- holder: Andres Salomon <dilinger@debian.org>
  years: '2005'
- holder: Frank Cusack <fcusack@fcusack.com>
  years: 1999-2000
description: |
  pam-krb5 provides a Kerberos PAM module that supports authentication, user
  ticket cache handling, simple authorization (via .k5login or checking
  Kerberos principals against local usernames), and password changing.  It
  can be configured through either options in the PAM configuration itself
  or through entries in the system krb5.conf file, and it tries to work
  around PAM implementation flaws in commonly-used PAM-enabled applications
  such as OpenSSH and xdm.  It supports both PKINIT and FAST to the extent
  that the underlying Kerberos libraries support these features.

  This is not the Kerberos PAM module maintained on Sourceforge and used on
  Red Hat systems.  It is an independent implementation that, if it ever
  shared any common code, diverged long ago.  It supports some features that
  the Sourceforge module does not (particularly around authorization), and
  does not support some options (particularly ones not directly related to
  Kerberos) that it does.  This module will never support Kerberos v4 or
  AFS.  For an AFS session module that works with this module (or any other
  Kerberos PAM module), see
  [pam-afs-session](https://www.eyrie.org/~eagle/software/pam-afs-session/).

  If there are other options besides AFS and Kerberos v4 support from the
  Sourceforge PAM module that you're missing in this module, please let me
  know.
distribution:
  packaging:
    debian:
      package: libpam-krb5
      summary: |
        Debian packages are available from Debian in Debian 4.0 (etch) and later
        releases as libpam-krb5 and libpam-heimdal.  The former packages are built
        against the MIT Kerberos libraries and the latter against the Heimdal
        libraries.
  section: kerberos
  tarname: pam-krb5
  version: pam-krb5
docs:
  user:
  - name: pam-krb5
    title: Manual page
format: v1
license:
  name: BSD-3-clause-or-GPL-1+
maintainer: Russ Allbery <eagle@eyrie.org>
name: pam-krb5
quote:
  author: Joyce McGreevy
  date: 2003-11-17
  text: |
    "You're always going to have some people who can't appreciate the thrill
    of a tepid change for the somewhat better," explained one source.
  title: '"Look, ma, no hands!"'
  work: Salon
requirements: |
  Either MIT Kerberos (or Kerberos implementations based on it) or Heimdal
  are supported.  MIT Keberos 1.3 or later may be required; this module has
  not been tested with earlier versions.

  For PKINIT support, Heimdal 0.8rc1 or later or MIT Kerberos 1.6.3 or later
  are required.  Earlier MIT Kerberos 1.6 releases have a bug in their
  handling of PKINIT options.

  For FAST (Flexible Authentication Secure Tunneling) support, MIT Kerberos
  1.7 or higher is required.  For anonymous FAST support, anonymous
  authentication (generally anonymous PKINIT) support is required in both
  the Kerberos libraries and in the local KDC.

  This module should work on Linux and Solaris (and build with gcc, clang,
  or the Sun C compiler), but has been far more heavily tested on Linux.
  There is beta-quality support for the AIX NAS Kerberos implementation.
  Other PAM implementations will probably require some porting, although
  untested build system support is present for FreeBSD, Mac OS X, and HP-UX.
  I personally can only test on Linux and rely on others to report problems
  on other operating systems.

  Old versions of OpenSSH are known to call `pam_authenticate` followed by
  `pam_setcred(PAM_REINITIALIZE_CRED)` without first calling
  `pam_open_session`, thereby requesting that an existing ticket cache be
  renewed (similar to what a screensaver would want) rather than requesting
  a new ticket cache be created.  Since this behavior is indistinguishable
  at the PAM level from a screensaver, pam-krb5 when used with these old
  versions of OpenSSH will refresh the ticket cache of the OpenSSH daemon
  rather than setting up a new ticket cache for the user.  The resulting
  ticket cache will have the correct permissions (this is not a security
  concern), but will not be named correctly or referenced in the user's
  environment and will be overwritten by the next user login.  The best
  solution to this problem is to upgrade OpenSSH.  I'm not sure exactly when
  this problem was fixed, but at the very least OpenSSH 4.3 and later do not
  exhibit it.
sections:
- body: |
    Just installing the module does not enable it or change anything about
    your system authentication configuration.  To use the module for all
    system authentication on Debian systems, put something like:

    ```
        auth  sufficient   pam_krb5.so minimum_uid=1000
        auth  required     pam_unix.so try_first_pass nullok_secure
    ```

    in `/etc/pam.d/common-auth`, something like:

    ```
        session  optional  pam_krb5.so minimum_uid=1000
        session  required  pam_unix.so
    ```

    in `/etc/pam.d/common-session`, and something like:

    ```
        account  required  pam_krb5.so minimum_uid=1000
        account  required  pam_unix.so
    ```

    in `/etc/pam.d/common-account`.  The `minimum_uid` setting tells the PAM
    module to pass on any users with a UID lower than 1000, thereby bypassing
    Kerberos authentication for the root account and any system accounts.  You
    normally want to do this since otherwise, if the network is down, the
    Kerberos authentication can time out and make it difficult to log in as
    root and fix matters.  This also avoids problems with Kerberos principals
    that happen to match system accounts accidentally getting access to those
    accounts.

    Be sure to include the module in the session group as well as the auth
    group.  Without the session entry, the user's ticket cache will not be
    created properly for ssh logins (among possibly others).

    If your users should normally all use Kerberos passwords exclusively,
    putting something like:

    ```
        password sufficient pam_krb5.so minimum_uid=1000
        password required   pam_unix.so try_first_pass obscure md5
    ```

    in `/etc/pam.d/common-password` will change users' passwords in Kerberos
    by default and then only fall back on Unix if that doesn't work.  (You can
    make this tighter by using the more complex new-style PAM configuration.)
    If you instead want to synchronize local and Kerberos passwords and change
    them both at the same time, you can do something like:

    ```
        password required   pam_unix.so obscure sha512
        password required   pam_krb5.so use_authtok minimum_uid=1000
    ```

    If you have multiple environments that you want to synchronize and you
    don't want password changes to continue if the Kerberos password change
    fails, use the `clear_on_fail` option.  For example:

    ```
        password required   pam_krb5.so clear_on_fail minimum_uid=1000
        password required   pam_unix.so use_authtok obscure sha512
        password required   pam_smbpass.so use_authtok
    ```

    In this case, if `pam_krb5` cannot change the password (due to password
    strength rules on the KDC, for example), it will clear the stored password
    (because of the `clear_on_fail` option), and since `pam_unix` and
    `pam_smbpass` are both configured with `use_authtok`, they will both fail.
    `clear_on_fail` is not the default because it would interfere with the
    more common pattern of falling back to local passwords if the user doesn't
    exist in Kerberos.

    If you use a more complex configuration with the Linux PAM `[]` syntax for
    the session and account groups, note that `pam_krb5` returns a status of
    ignore, not success, if the user didn't log on with Kerberos.  You may
    need to handle that explicitly with `ignore=ignore` in your action list.

    There are many, many other possibilities.  See the Linux PAM documentation
    for all the configuration options.

    On Red Hat systems, modify `/etc/pam.d/system-auth` instead, which
    contains all of the configuration for the different stacks.

    You can also use pam-krb5 only for specific services.  In that case,
    modify the files in `/etc/pam.d` for that particular service to use
    `pam_krb5.so` for authentication.  For services that are using passwords
    over TLS to authenticate users, you may want to use the `ignore_k5login`
    and `no_ccache` options to the authenticate module.  `.k5login`
    authorization is only meaningful for local accounts and ticket caches are
    usually (although not always) only useful for interactive sessions.

    Configuring the module for Solaris is both simpler and less flexible,
    since Solaris (at least Solaris 8 and 9, which are the last versions of
    Solaris with which this module was extensively tested) use a single
    `/etc/pam.conf` file that contains configuration for all programs.  For
    console login on Solaris, try something like:

    ```
        login auth sufficient /usr/local/lib/security/pam_krb5.so minimum_uid=100
        login auth required /usr/lib/security/pam_unix_auth.so.1 use_first_pass
        login account required /usr/local/lib/security/pam_krb5.so minimum_uid=100
        login account required /usr/lib/security/pam_unix_account.so.1
        login session required /usr/local/lib/security/pam_krb5.so retain_after_close minimum_uid=100
        login session required /usr/lib/security/pam_unix_session.so.1
    ```

    A similar configuration could be used for other services, such as ssh.
    See the pam.conf(5) man page for more information.  When using this module
    with Solaris login (at least on Solaris 8 and 9), you will probably also
    need to add `retain_after_close` to the PAM configuration to avoid having
    the user's credentials deleted before they are logged in.

    The Solaris Kerberos library reportedly does not support prompting for a
    password change of an expired account during authentication.  Supporting
    password change for expired accounts on Solaris with native Kerberos may
    therefore require setting the `defer_pwchange` or `force_pwchange` option
    for selected login applications.  See the description and warnings about
    that option in the pam_krb5(5) man page.

    Some configuration options may be put in the `krb5.conf` file used by your
    Kerberos libraries (usually `/etc/krb5.conf` or
    `/usr/local/etc/krb5.conf`) instead or in addition to the PAM
    configuration.  See the man page for more details.

    The Kerberos library, via pam-krb5, will prompt the user to change their
    password if their password is expired, but when using OpenSSH, this will
    only work when `ChallengeResponseAuthentication` is enabled.  Unless this
    option is enabled, OpenSSH doesn't pass PAM messages to the user and can
    only respond to a simple password prompt.

    If you are using MIT Kerberos, be aware that users whose passwords are
    expired will not be prompted to change their password unless the KDC
    configuration for your realm in `[realms]` in `krb5.conf` contains a
    `master_kdc` setting or, if using DNS SRV records, you have a DNS entry
    for `_kerberos-master` as well as `_kerberos`.
  title: Configuring
- body: |
    The first step when debugging any problems with this module is to add
    `debug` to the PAM options for the module (either in the PAM configuration
    or in `krb5.conf`).  This will significantly increase the logging from the
    module and should provide a trace of exactly what failed and any available
    error information.

    Many Kerberos authentication problems are due to configuration issues in
    `krb5.conf`.  If pam-krb5 doesn't work, first check that `kinit` works on
    the same system.  That will test your basic Kerberos configuration.  If
    the system has a keytab file installed that's readable by the process
    doing authentication via PAM, make sure that the keytab is current and
    contains a key for `host/<system>` where <system> is the fully-qualified
    hostname.  pam-krb5 prevents KDC spoofing by checking the user's
    credentials when possible, but this means that if a keytab is present it
    must be correct or authentication will fail.  You can check the keytab
    with `klist -k` and `kinit -k`.

    Be sure that all libraries and modules, including PAM modules, loaded by a
    program use the same Kerberos libraries.  Sometimes programs that use PAM,
    such as current versions of OpenSSH, also link against Kerberos directly.
    If your sshd is linked against one set of Kerberos libraries and pam-krb5
    is linked against a different set of Kerberos libraries, this will often
    cause problems (such as segmentation faults, bus errors, assertions, or
    other strange behavior).  Similar issues apply to the com_err library or
    any other library used by both modules and shared libraries and by the
    application that loads them.  If your OS ships Kerberos libraries, it's
    usually best if possible to build all Kerberos software on the system
    against those libraries.
  title: Debugging
- body: |
    The normal sequence of actions taken for a user login is:

    ```
        pam_authenticate
        pam_setcred(PAM_ESTABLISH_CRED)
        pam_open_session
        pam_acct_mgmt
    ```

    and then at logout:

    ```
        pam_close_session
    ```

    followed by closing the open PAM session.  The corresponding `pam_sm_*`
    functions in this module are called when an application calls those public
    interface functions.  Not all applications call all of those functions, or
    in particularly that order, although `pam_authenticate` is always first
    and has to be.

    When `pam_authenticate` is called, pam-krb5 creates a temporary ticket
    cache in `/tmp` and sets the PAM environment variable `PAM_KRB5CCNAME` to
    point to it.  This ticket cache will be automatically destroyed when the
    PAM session is closed and is there only to pass the initial credentials to
    the call to `pam_setcred`.  The module would use a memory cache, but
    memory caches will only work if the application preserves the PAM
    environment between the calls to `pam_authenticate` and `pam_setcred`.
    Most do, but OpenSSH notoriously does not and calls `pam_authenticate` in
    a subprocess, so this method is used to pass the tickets to the
    `pam_setcred` call in a different process.

    `pam_authenticate` does a complete authentication, including checking the
    resulting TGT by obtaining a service ticket for the local host if
    possible, but this requires read access to the system keytab.  If the
    keytab doesn't exist, can't be read, or doesn't include the appropriate
    credentials, the default is to accept the authentication.  This can be
    controlled by setting `verify_ap_req_nofail` to true in `[libdefaults]` in
    `/etc/krb5.conf`.  `pam_authenticate` also does a basic authorization
    check, by default calling `krb5_kuserok` (which uses `~/.k5login` if
    available and falls back to checking that the principal corresponds to the
    account name).  This can be customized with several options documented in
    the pam_krb5(5) man page.

    pam-krb5 treats `pam_open_session` and `pam_setcred(PAM_ESTABLISH_CRED)`
    as synonymous, as some applications call one and some call the other.
    Both copy the initial credentials from the temporary cache into a
    permanent cache for this session and set `KRB5CCNAME` in the environment.
    It will remember when the credential cache has been established and then
    avoid doing any duplicate work afterwards, since some applications call
    `pam_setcred` or `pam_open_session` multiple times (most notably X.Org 7
    and earlier xdm, which also throws away the module settings the last time
    it calls them).

    `pam_acct_mgmt` finds the ticket cache, reads it in to obtain the
    authenticated principal, and then does is another authorization check
    against `.k5login` or the local account name as described above.

    After the call to `pam_setcred` or `pam_open_session`, the ticket cache
    will be destroyed whenever the calling application either destroys the PAM
    environment or calls `pam_close_session`, which it should do on user
    logout.

    The normal sequence of events when refreshing a ticket cache (such as
    inside a screensaver) is:

    ```
        pam_authenticate
        pam_setcred(PAM_REINITIALIZE_CRED)
        pam_acct_mgmt
    ```

    (`PAM_REFRESH_CRED` may be used instead.)  Authentication proceeds as
    above.  At the `pam_setcred` stage, rather than creating a new ticket
    cache, the module instead finds the current ticket cache (from the
    `KRB5CCNAME` environment variable or the default ticket cache location
    from the Kerberos library) and then reinitializes it with the credentials
    from the temporary `pam_authenticate` ticket cache.  When refreshing a
    ticket cache, the application should not open a session.  Calling
    `pam_acct_mgmt` is optional; pam-krb5 doesn't do anything different when
    it's called in this case.

    If `pam_authenticate` apparently didn't succeed, or if an account was
    configured to be ignored via `ignore_root` or `minimum_uid`, `pam_setcred`
    (and therefore `pam_open_session`) and `pam_acct_mgmt` return
    `PAM_IGNORE`, which tells the PAM library to proceed as if that module
    wasn't listed in the PAM configuration at all.  `pam_authenticate`,
    however, returns failure in the ignored user case by default, since
    otherwise a configuration using `ignore_root` with pam-krb5 as the only
    PAM module would allow anyone to log in as root without a password.  There
    doesn't appear to be a case where returning `PAM_IGNORE` instead would
    improve the module's behavior, but if you know of a case, please let me
    know.

    By default, `pam_authenticate` intentionally does not follow the PAM
    standard for handling expired accounts and instead returns failure from
    `pam_authenticate` unless the Kerberos libraries are able to change the
    account password during authentication.  Too many applications either do
    not call `pam_acct_mgmt` or ignore its exit status.  The fully correct PAM
    behavior (returning success from `pam_authenticate` and
    `PAM_NEW_AUTHTOK_REQD` from `pam_acct_mgmt`) can be enabled with the
    `defer_pwchange` option.

    The `defer_pwchange` option is unfortunately somewhat tricky to implement.
    In this case, the calling sequence is:

    ```
        pam_authenticate
        pam_acct_mgmt
        pam_chauthtok
        pam_setcred
        pam_open_session
    ```

    During the first `pam_authenticate`, we can't obtain credentials and
    therefore a ticket cache since the password is expired.  But
    `pam_authenticate` isn't called again after `pam_chauthtok`, so
    `pam_chauthtok` has to create a ticket cache.  We however don't want it to
    do this for the normal password change (`passwd`) case.

    What we do is set a flag in our PAM data structure saying that we're
    processing an expired password, and `pam_chauthtok`, if it sees that flag,
    redoes the authentication with password prompting disabled after it
    finishes changing the password.

    Unfortunately, when handling password changes this way, `pam_chauthtok`
    will always have to prompt the user for their current password again even
    though they just typed it.  This is because the saved authentication
    tokens are cleared after `pam_authenticate` returns, for security reasons.
    We could hack around this by saving the password in our PAM data
    structure, but this would let the application gain access to it (exactly
    what the clearing is intended to prevent) and breaks a PAM library
    guarantee.  We could also work around this by having `pam_authenticate`
    get the `kadmin/changepw` authenticator in the expired password case and
    store it for `pam_chauthtok`, but it doesn't seem worth the hassle.
  title: Implementation Notes
- body: |
    Originally written by Frank Cusack <fcusack@fcusack.com>, with the
    following acknowledgement:

    > Thanks to Naomaru Itoi <itoi@eecs.umich.edu>, Curtis King
    > <curtis.king@cul.ca>, and Derrick Brashear <shadow@dementia.org>, all of
    > whom have written and made available Kerberos 4/5 modules.  Although no
    > code in this module is directly from these author's modules, (except the
    > get_user_info() routine in support.c; derived from whichever of these
    > authors originally wrote the first module the other 2 copied from), it
    > was extremely helpful to look over their code which aided in my design.

    The module was then patched for the FreeBSD ports collection with
    additional modifications by unknown maintainers and then was modified by
    Joel Kociolek <joko@logidee.com> to be usable with Debian GNU/Linux.

    It was packaged by Sam Hartman as the Kerberos v5 PAM module for Debian
    and improved and modified by him and later by Russ Allbery to fix bugs and
    add additional features.  It was then adopted by Andres Salomon, who added
    support for refreshing credentials.

    The current distribution is maintained by Russ Allbery, who also added
    support for reading configuration from `krb5.conf`, added many features
    for compatibility with the Sourceforge module, commented and standardized
    the formatting of the code, and overhauled the documentation.

    Thanks to Douglas E. Engert for the initial implementation of PKINIT
    support.  I have since modified and reworked it extensively, so any bugs
    or compilation problems are my fault.

    Thanks to Markus Moeller for lots of debugging and multiple patches and
    suggestions for improved portability.

    Thanks to Booker Bense for the implementation of the `alt_auth_map`
    option.

    Thanks to Sam Hartman for the FAST support implementation.
  title: History and Acknowledgements
support:
  email: eagle@eyrie.org
  github: rra/pam-krb5
  web: https://www.eyrie.org/~eagle/software/pam-krb5/
synopsis: PAM module for Kerberos authentication
test:
  prefix: |
    pam-krb5 comes with a comprehensive test suite, but it requires some
    configuration in order to test anything other than low-level utility
    functions.  For the full test suite, you will need to have a running KDC
    in which you can create two test accounts, one with admin access to the
    other.  Using a test KDC environment, if you have one, is recommended.

    Follow the instructions in `tests/config/README` to configure the test
    suite.

    Now, you can run the test suite with:
  suffix: |
    The default libkadm5clnt library on the system must match the
    implementation of your KDC for the module/expired test to work, since the
    two kadmin protocols are not compatible.  If you use the MIT library
    against a Heimdal server, the test will be skipped; if you use the Heimdal
    library against an MIT server, the test suite may hang.

    Several `module/expired` tests are expected to fail with Heimdal 1.5 due
    to a bug in Heimdal with reauthenticating immediately after a
    library-mediated password change of an expired password.  This is fixed in
    later releases of Heimdal.
vcs:
  browse: https://git.eyrie.org/?p=kerberos/pam-krb5.git
  github: rra/pam-krb5
  openhub: https://www.openhub.net/p/pamkrb5
  type: Git
  url: https://git.eyrie.org/git/kerberos/pam-krb5.git
version: '4.8'
