# Package metadata for pam-krb5. # # This file contains configuration for DocKnot used to generate # documentation files (like README.md) and web pages. Other documentation # in this package is generated automatically from these files as part of # the release process. For more information, see DocKnot's documentation. # # DocKnot is available from . # # Copyright 2017, 2020-2021 Russ Allbery # # SPDX-License-Identifier: BSD-3-clause or GPL-1+ format: v1 name: pam-krb5 maintainer: Russ Allbery version: '4.11' synopsis: PAM module for Kerberos authentication license: name: BSD-3-clause-or-GPL-1+ copyrights: - holder: Russ Allbery years: 2005-2010, 2014-2015, 2017, 2020-2021 - holder: The Board of Trustees of the Leland Stanford Junior University years: 2009-2011 - holder: Andres Salomon years: '2005' - holder: Frank Cusack years: 1999-2000 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, but expect to have to override this using `--libdir`. The correct installation path for PAM modules varies considerably between systems. The module will always be installed in a subdirectory named `security` under the specified value of `--libdir`. On Red Hat Linux, for example, `--libdir=/usr/lib64` is appropriate to install the module into the system PAM directory. On Debian's amd64 architecture, `--libdir=/usr/lib/x86_64-linux-gnu` would be correct. reduced_depends: true type: Autoconf valgrind: true 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 support: email: eagle@eyrie.org github: rra/pam-krb5 web: https://www.eyrie.org/~eagle/software/pam-krb5/ vcs: browse: https://git.eyrie.org/?p=kerberos/pam-krb5.git github: rra/pam-krb5 openhub: https://www.openhub.net/p/pamkrb5 status: workflow: build type: Git url: https://git.eyrie.org/git/kerberos/pam-krb5.git 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 advisories: - date: 2020-03-30 threshold: '4.9' versions: 4.8 and earlier - date: 2009-02-11 threshold: '3.13' versions: 3.12 and earlier docs: user: - name: pam-krb5 title: Manual page 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. 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. 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. MIT Kerberos 1.12 or later is required to use the use_pkinit PAM option. 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 build with gcc or clang. It may still work on Solaris and build with the Sun C compiler, but I have only tested it on Linux recently. There is beta-quality support for the AIX NAS Kerberos implementation that has not been tested in years. 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. test: lancaster: true 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. To run the full test suite, Perl 5.10 or later is required. The following additional Perl modules will be used if present: * Test::Pod * Test::Spelling All are available on CPAN. Those tests will be skipped if the modules are not available. sections: - title: Configuring 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: Debugging 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/` where 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: Implementation Notes 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: History and Acknowledgements body: | Originally written by Frank Cusack , with the following acknowledgement: > Thanks to Naomaru Itoi , Curtis King > , and Derrick Brashear , 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 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.