1PAM_U2F(8) PAM U2F Module Manual PAM_U2F(8)
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6 pam_u2f - Module for U2F authentication
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9 pam_u2f [...]
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12 The module provides U2F authentication against Yubikeys and other
13 compliant authenticators.
14
16 debug
17 Enables debug output
18 debug_file
20 Filename to write debug to, file must exist and be a regular file,
21 or one of "stdout", "stderr", or "syslog". STDERR is the default.
22 origin=origin
24 Set the origin for the U2F authentication procedure. If no value is
25 specified, the origin "pam://$HOSTNAME" is used.
26 appid=appid
28 Set the application ID for the U2F authentication procedure. If no
29 value is specified, the same value used for origin is taken
30 ("pam://$HOSTNAME" if also origin is not specified).
31 authfile=file
33 Set the location of the file that holds the mappings of user names
34 to keyHandles and user keys. The format is
35 username:keyHandle1,public_key1:keyHandle2,public_key2:... the
36 default location of the file is $XDG_CONFIG_HOME/Yubico/u2f_keys.
37 If the environment variable is not set,
38 $HOME/.config/Yubico/u2f_keys is used.
39 authpending_file=file
41 Set the location of the file that is used for touch request
42 notifications. This file will be opened when pam-u2f starts waiting
43 for a user to touch the device, and will be closed when it no
44 longer waits for a touch. Use inotify to listen on these events, or
45 a more high-level tool like yubikey-touch-detector. Default value:
46 /var/run/user/$UID/pam-u2f-authpending. Set an empty value in order
47 to disable this functionality, like so: "authpending_file=".
48 nouserok
50 Set to enable authentication attempts to succeed even if the user
51 trying to authenticate is not found inside authfile or if authfile
52 is missing/malformed.
53 openasuser
55 Setuid to the authenticating user when opening the authfile. Useful
56 when the user’s home is stored on an NFS volume mounted with the
57 root_squash option (which maps root to nobody which will not be
58 able to read the file). Note that after release 1.0.8 this is done
59 by default when no global authfile or XDG_CONFIG_HOME environment
60 variable has been set.
61 alwaysok
63 Set to enable all authentication attempts to succeed (aka
64 presentation mode).
65 max_devices=n_devices
67 Maximum number of devices allowed per user (default is 24). Devices
68 specified in the authentication file that exceed this value will be
69 ignored.
70 interactive
72 Set to prompt a message and wait before testing the presence of a
73 U2F device. Recommended if your device doesn’t have tactile
74 trigger.
75 [prompt=your prompt here]
77 Set individual prompt message for interactive mode. Watch the
78 square brackets around this parameter to get spaces correctly
79 recognized by PAM.
80 manual
82 Set to drop to a manual console where challenges are printed on
83 screen and response read from standard input. Useful for debugging
84 and SSH sessions without U2F-support from the SSH client/server. If
85 enabled, interactive mode becomes redundant and has no effect.
86 cue
88 Set to prompt a message to remind to touch the device.
89 nodetect
91 Skip detecting if a suitable key is inserted before performing a
92 full authentication. See NOTES below.
93
95 auth sufficient pam_u2f.so debug origin=pam://$HOSTNAME
96 appid=pam://$HOSTNAME
97 auth required pam_u2f.so origin=http://example.com
99 appid=http://example.com authfile=/etc/yubikey_mappings
100
102 By default the mapping file inside a home directory will be opened as
103 the target user, whereas the central file will be opened as root. If
104 the XDG_CONFIG_HOME variable is set, privileges will not be dropped
105 unless the openasuser configuration setting is set.
106 Using pam-u2f to secure the login to a computer while storing the
108 mapping file in an encrypted home directory, will result in the
109 impossibility of logging into the system. The partition is decrypted
110 after login and the mapping file can not be accessed.
111
113 The "nodetect" option should be used with caution. pam_u2f checks that
114 a key configured for the user is inserted before performing the full
115 tactile authentication. This detection is done by sending a
116 "check-only" authentication request to all inserted tokens to so see if
117 at least one of them responds affirmatively to one or more of the
118 keyhandles configured for the user. By doing this, pam_u2f can avoid
119 emitting the "cue" prompt (if configured), which can cause some
120 confusing UI issues if the cue is emitted followed by the underlying
121 library immediately failing the tactile authentication. This option is
122 also useful to avoid an unintended 1-second delay prior to the tactile
123 authentication caused by versions of libu2f-host <= 1.1.5.
124 If pam_u2f is configured to "cue" and "nodetect", an attacker can
126 determine that pam_u2f is part of the authentication stack by inserting
127 any random U2F token and performing an authentication attempt. In this
128 scenario, the attacker would see the cue message followed by an
129 immediate failure, whereas with detection enabled, the U2F
130 authentication will fail silently. Understand that an attacker could
131 choose a U2F token that alerts him or her in some way to the
132 "check-only" authentication attempt, so this precaution only pushes the
133 issue back a step.
134 In summary, the detection feature was added to avoid confusing UI
136 issues and to prevent leaking information about the authentication
137 stack in very specific scenario when "cue" is configured. The
138 "nodetect" option was added to avoid buggy sleep behavior in older
139 versions of libu2f-host and for hypothetical tokens that do not
140 tolerate the double authentication. Detection is performed, and
141 likewise "nodetect" honored, regardless of whether "cue" is also
142 specified.
143
145 Report pam-u2f bugs in the issue tracker:
146 https://github.com/Yubico/pam-u2f/issues
147
149 pam(7)
150 The pam-u2f home page: https://developers.yubico.com/pam-u2f/
152 YubiKeys can be obtained from Yubico: http://www.yubico.com/
154pam-u2f Version 1.0.8 PAM_U2F(8)