source: trunk/man/samhain.8@ 9

.TH SAMHAIN 8 "07 August 2004" "" "Samhain manual"
.SH NAME
samhain \- check file integrity
.SH SYNOPSIS
.SS "INITIALIZING, UPDATING, AND CHECKING"
.PP

.B samhain 
{
.I \-t init|\-\-set\-checksum\-test=init
} [\-\-init2stdout] [\-r DEPTH|\-\-recursion=DEPTH] [log-options]

.B samhain 
{
.I \-t update|\-\-set\-checksum\-test=update
} [\-D | \-\-daemon | \-\-foreground] [\-\-forever] [\-r DEPTH|\-\-recursion=DEPTH] [log-options]

.B samhain 
{
.I \-t check|\-\-set\-checksum\-test=check
} [\-D | \-\-daemon | \-\-foreground] [\-\-forever] [\-r DEPTH,\-\-recursion=DEPTH] [log-options]

.SS "LISTING THE DATABASE"
.PP

.B samhain 
[\-a | \-\-full\-detail]
[\-\-delimited]
\-d 
.IR file | 
.RI \-\-list\-database= file 

.SS "VERIFYING AN AUDIT TRAIL"
.PP

.B samhain 
[\-j | \-\-just\-list]
\-L 
.IR logfile | 
.RI \-\-verify\-log= logfile 

.B samhain 
\-M 
.IR mailbox | 
.RI \-\-verify\-mail= mailbox 


.SS "MISCELLANEOUS"
.PP

.B samhain
\-H 
.I string 
| 
.RI \-\-hash\-string= string 

.B samhain
\-c | \-\-copyright

.B samhain
\-h | \-\-help 

.B samhain
\-V key@/path/to/executable | \-\-add\-key=key@/path/to/executable

.SS "SERVER STARTUP"
.PP

.B yule
[\-q | \-\-qualified]
[
.RI \-\-chroot= chrootdir ]
[\-D | \-\-daemon | \-\-foreground]
[log-options]

.SS "SERVER MISCELLANEOUS"
.PP

.B yule
[\-P 
.I password 
| 
.RI \-\-password= password ]

.B yule
[\-G | \-\-gen-password]

.SS "LOG OPTIONS"
.PP

[\-s 
.I threshold 
| 
.RI \-\-set\-syslog\-severity= threshold ] 
[\-l 
.I threshold 
| 
.RI \-\-set\-log\-severity= threshold ] 
[\-m 
.I threshold 
| 
.RI \-\-set\-mail\-severity= threshold ] 
[\-e 
.I threshold 
| 
.RI \-\-set\-export\-severity= threshold ] 
[\-p 
.I threshold 
| 
.RI \-\-set\-print\-severity= threshold ] 
[\-x 
.I threshold 
| 
.RI \-\-set\-external\-severity= threshold ] 
[
.RI \-\-set\-prelude\-severity= threshold ] 
[
.RI \-\-set\-database\-severity= threshold ] 
[
.RI \-\-enable\-trace ]
[
.RI \-\-trace\-logfile= tracefile ]



.SH WARNING
.PP
The information in this man page is not always up to date.
The authoritative documentation is the user manual.

.SH DESCRIPTION
.PP
.B samhain
is a file integrity / intrusion detection system both for single hosts 
and networks.
It consists of a monitoring application 
.RB ( samhain ) 
running on
individual hosts, and (optionally) a central log server
.RB ( yule ). 
Currently, samhain can monitor the 
integrity of files/directories, and (optionally) also 
check for kernel rootkits 
(Linux and FreeBSD only), search the disk for SUID/SGID, 
and watch for login/logout events.
.PP
.B samhain/yule
can log by email, to a tamper-resistant, signed log file, 
to syslog, to the Prelude IDS, to a MySQL/PostgreSQL/Oracle database,
and/or to stdout 
.RI ( /dev/console 
if run as daemon).
.B samhain/yule
can run as a daemon, and can use a time server instead of the host's
system clock. Most of the functionality is defined by a 
configuration file that is read at startup.
.PP
Most options of these usually would be set in the configuration file. 
Options given on the command line will override
those in the configuration file. 

.SS "OPTIONS FOR INITIALIZING, UPDATING, AND CHECKING"
.PP

.B samhain
.I "\-t init, \-\-set\-checksum-test=init"
.RI [ options ]

Initialize the database of file signatures. The path to the
database is compiled in, and initializing will
.B append 
to the respective file (or create it, if it does not exist).
.B "It is ok to append to e.g. a JPEG image, but it is an error"
.B "to append to an already existing file signature database."
.PP
.TP
[\-\-init2stdout]
Write the database to stdout. 
.TP
[\-r DEPTH|\-\-recursion=DEPTH]
Set the (global) recursion depth.

.PP
.B samhain
.I "\-t update, \-\-set\-checksum-test=update"
.RI [ options ]

Update the database of file signatures. The path to the
database is compiled in, and updating will 
.B overwrite 
the database, starting from the start of the database (which may not be
identical to the start of the file \- see above).
.PP
.TP
[\-r DEPTH|\-\-recursion=DEPTH]
Set the (global) recursion depth.
.TP
[\-D|\-\-daemon]
Run as daemon. File checks are performed as specified by the timing
options in the configuration file. Updates are saved after each file check.
.TP
[\-\-foreground]
Run in the foreground. This will cause samhain to exit after the update,
unless the option
.I "\-\-forever"
is used.
.TP
[\-\-forever]
If not running as daemon, do not exit after finishing the update, but
loop forever, and perform checks with corresponding database updates
according to the timing options in the
configuration file.

.PP
.B samhain
.I "\-t check, \-\-set\-checksum-test=check"
.RI [ options ]

Check the filesystem against the database of file signatures. 
The path to the database is compiled in.
.PP
.TP
[\-r DEPTH|\-\-recursion=DEPTH]
Set the (global) recursion depth.
.TP
[\-D|\-\-daemon]
Run as daemon. File checks are performed as specified by the timing
options in the configuration file.
.TP
[\-\-foreground]
Run in the foreground. This will cause samhain to exit after the file check,
unless the option
.I "\-\-forever"
is used.
.TP
[\-\-forever]
If not running as daemon, do not exit after finishing the check, but
loop forever, and perform checks according to the timing options in the
configuration file.

.SS "OPTIONS FOR LISTING THE DATABASE"
.PP

.B samhain 
[\-a | \-\-full\-detail]
[\-\-delimited]
\-d 
.IR file | 
.RI \-\-list\-database= file 

List the entries in the file signature database in a 
.B ls \-l
like format.
.PP
.TP
[\-a | \-\-full\-detail]
List all informations for each file, not only those you would get
with ls \-l.
.TP
[\-\-delimited]
List all informations for each file, in a comma-separated format.

.SS "OPTIONS TO VERIFY AN AUDIT TRAIL"
.PP

These options will only work, if the executable used for verifying the
audit trail is compiled with the same \-\-enable\-base=... option as the
executable of the reporting process.

.B samhain 
[\-j | \-\-just\-list]
\-L 
.IR logfile | 
.RI \-\-verify\-log= logfile 

Verify the integrity of a signed logfile. The signing key is 
auto\-generated on startup, and sent by email.
.B samhain
will ask for the key. Instead of entering the key, you can also enter
the path to the mailbox holding the respective email message.
.PP
.TP
[\-j | \-\-just\-list]
Just list the logfile, do not verify it. This option must come
.BR first .
It is mainly intended for listing the content of an obfuscated logfile, if
.B samhain
is compiled with the 
.B stealth
option.

.B samhain 
\-M 
.IR mailbox | 
.RI \-\-verify\-mail= mailbox 

Verify the integrity of the email reports from samhain. All reports must be
in the same file.

.SS "MISCELLANEOUS OPTIONS"
.PP

.B samhain
\-H 
.I string 
| 
.RI \-\-hash\-string= string

Compute the TIGER192 checksum of a string. If the string starts with
a '/', it is considered as a pathname, and the checksum of the corresponding
file will be computed. 

.B samhain
\-c | \-\-copyright

Print the copyright statement.

.B samhain
\-h | \-\-help 

Print supported options (depending on compilation options).

.B samhain
\-V key@/path/to/executable | \-\-add\-key=key@/path/to/executable

See the section "SECURITY" below.

.SS "SERVER STARTUP OPTIONS"
.PP

.B yule
[\-q | \-\-qualified]
[
.RI \-\-chroot= chrootdir ]
[\-D | \-\-daemon | \-\-foreground]
[log-options]

Start the server, which is named
.B yule
by default. If the server is started with superuser privileges,
it will drop them after startup.
.PP
.TP
[\-q | \-\-qualified]
Log client hostnames with fully qualified path. The default is to
log only the leftmost domain label (i.e. the hostname).
.TP
[
.RI \-\-chroot= chrootdir ]
Chroot to the listed directory after startup.
.TP
[\-D | \-\-daemon]
Run as daemon.
.TP
[\-\-foreground]
Run in the foreground.


.SS "MISCELLANEOUS SERVER OPTIONS"
.PP

.B yule
[\-G | \-\-gen-password]

Generate a random 8\-byte password and print it out in hexadecimal notation.


.B yule
[\-P 
.I password 
| 
.RI \-\-password= password ]

Use the given 
.I password
and generate an entry suitable for the [Clients] section of the
configuration file.

.SS "LOGGING OPTIONS"
.PP

Depending on the compilation options, some logging facilities may not
be available in your executable.
.PP
.TP
.I "\-s threshold, \-\-set\-syslog\-severity=threshold"
Set the threshold for logging events via syslogd(8).
Possible values are
.IR debug ,
.IR info ,
.IR notice ,
.IR warn ,
.IR mark ,
.IR err ,
.IR crit ,
.IR alert ,
and
.IR none .
By default, everything equal to and above the threshold will be logged. 
Time stamps have the priority 
.IR warn , 
system\-level errors have the priority
.IR err ,
and important start\-up messages the priority
.IR alert .
The signature key for the log file will never be logged to syslog or the
log file itself.
.TP
.I "\-l threshold, \-\-set\-log\-severity=threshold"
Set the threshold for logging events to the log file. 
.TP
.I "\-m threshold, \-\-set\-mail\-severity=threshold"
Set the threshold for logging events via e\-mail. 
.TP
.I "\-e threshold, \-\-set\-export\-severity=threshold"
Set the threshold for forwarding events via TCP to a log server. 
.TP
.I "\-x threshold, \-\-set\-extern\-severity=threshold"
Set the threshold for calling external logging programs/scripts (if any are
defined in the configuration file). 
.TP
.I "\-p threshold, \-\-set\-print\-severity=threshold"
Set the threshold for logging events to stdout. 
If
.B samhain
runs as a daemon, this is redirected to /dev/console.
.TP
.I "\-\-set\-prelude\-severity=threshold"
Set the threshold for logging events to the Prelude IDS.
.TP
.I "\-\-set\-database\-severity=threshold"
Set the threshold for logging events to the MySQL/PostgreSQL/Oracle 
database.



.SH SIGNALS
.TP
.I SIGUSR1
Switch on/off maximum verbosity for console output.
.TP
.I SIGUSR2
Suspend/continue the process, and 
(on suspend) send a message
to the server. This message has the same priority as timestamps. 
This signal
allows to run 
.I samhain -t init -e none
on the client
to regenerate the database, with download of the configuration file
from the server, while the daemon is suspended (normally you would get
errors because of concurrent access to the server by two processes from
the 
.IR "same host" ")."
.TP
.I SIGHUP
Reread the configuration file.
.TP
.I SIGTERM
Terminate.
.TP
.I SIGQUIT
Terminate after processing all pending requests from clients.
.TP
.I SIGABRT
Unlock the log file, pause for three seconds, then proceed,
eventually re-locking the log file and starting a fresh audit trail
on next access.
.TP
.I SIGTTOU
Force a file check (only client/standalone, and only in daemon mode).


.SH DATABASE
The database (default name
.IR samhain_file )
is a binary file, which can be created or updated using the 
.B \-t 
.I init
or the
.B \-t 
.I update
option. 
If you use 
.B \-t 
.IR init ,
you need to 
.I remove
the old database first,
otherwise the new version will be 
.I appended 
to the old one.
The file may be (clear text) signed by PGP/GnuPG.
.br
It is recommended to use GnuPG with the options
.B gpg
.I -a --clearsign --not-dash-escaped
.br
.B samhain
will check the signature, if compiled with support for that.
.PP
At startup 
.B samhain
will compute the checksum of the database, and verify it for
each further access. This checksum is not stored on disk (i.e. is lost
after program termination), as there is no secure way to store it.

.SH LOG FILE
.PP
Each entry in the log file has the format
.BR "Severity : [Timestamp] Message" ,
where the timestamp may be obtained from a time server rather than from
the system clock, if 
.B samhain
has been compiled with support for this.
Each entry is followed by a 
.IR signature ,
which is computed as
.BR "Hash(Entry Key_N)" ,
and 
.B  Key_N
is computed as
.BR "Hash(Key_N\-1)" ,
i.e. only knowledge of the first signature key in this chain allows to
verify the integrity of the log file. This first key is autogenerated
and e\-mailed to the designated recipient.
.PP
The default name of the log file is
.IR samhain_log .
To prevent multiple instances of
.B samhain
from writing to the same log file, the log file is locked by creating a 
.IR "lock file" , 
which is normally deleted at program termination. 
The default name of the
.I "lock file" 
is
.IR samhain.lock .
If 
.B samhain
is terminated abnormally, i.e. with kill \-9,
a stale lock file might remain, but usually
.B samhain
will be able to recognize that and remove the stale lock file
on the next startup.
.PP
.SH EMAIL
.PP
E\-mails are sent (using built-in SMTP code)
to one recipient only.
The subject line contains timestamp
and hostname, which are repeated in the message body. 
The body of the mail contains a line with a 
.I signature
similar to that in the log file, computed from the message and a
key. The key is iterated by a hash chain, and the initial
key is revealed in the first email sent.
Obviously, you have to believe that this first e\-mail is
authentical ... 
.PP
.SH CLIENT/SERVER USAGE
.PP
To monitor several machines, and collecting data by a central log server,
.B samhain
may be compiled as a client/server application. The log server 
.RB ( yule )
will accept connection
requests from registered clients only. With each client, the server will first
engage in a challenge/response protocol for 
.I authentication 
of the client and 
.I establishing
a 
.IR "session key" .
.PP
This protocol requires on the client side a 
.IR "password" ,
and on the server side a
.IR "verifier" 
that is computed from the
.IR "password" .
.PP
To 
.I register 
a client, simply do the following:
.br
First, with the included utility program 
.B samhain_setpwd
re\-set the compiled\-in default password of the 
client executable to your preferred
value (with no option, a short usage help is printed). 
To allow for non-printable chars, the new value
must be given as a 16\-digit hexadecimal string 
(only 0123456789ABCDEF in string), corresponding to an 8-byte password.
.br
Second, after re\-setting the password in the client executable,
you can use the server's convenience function 
.B yule
.B \-P 
.I password 
that will take as input the (16\-digit hex) password, 
compute the corresponding verifier, and outputs a default configuration file
entry to register the client.
.br
Third, in the configuration file for the server, under the [Clients] section,
enter
the suggested registration entry of the form 
.IR "Client=hostname@salt@verifier" ,
where
.I hostname 
must be the (fully qualified) hostname of the machine on 
which the client will run.
.B "Don't forget to reload the server configuration thereafter." 
.PP
If a connection attempt is made, the server will lookup the entry for
the connecting host, and use the corresponding value for the 
.I verifier 
to engage in the session key exchange. Failure to verify the client's
response(s) will result in aborting the connection.
.PP
.SH STEALTH
.PP
.B samhain 
may be compiled with support for a 
.I stealth 
mode of operation, meaning that
the program can be run without any obvious trace of its presence
on disk. The supplied facilities are simple - they are more
sophisticated than just running the program under a different name,
and might thwart efforts using 'standard' Unix commands,
but they will not resist a search using dedicated utilities. 
.PP
In this mode, the runtime executable will hold no
printable strings, and the configuration file is expected to be
a postscript file with 
.I uncompressed 
image data, wherein 
the configuration data are hidden by steganography.
To create such a file from an existing image, you may use e.g. 
the program 
.BR convert (1), 
which is part of the 
.BR ImageMagick (1) 
package, such as:
.B "convert +compress"
.IR "ima.jpg ima.ps" .
.PP
To hide/extract the configuration data within/from the postscript file,
a utility program
.B samhain_stealth 
is provided.
Use it without options to get help.
.PP
Database and log file may be e.g. existing image files, to which
data are appended, xor'ed with some constant to mask them as binary data.
.PP
The user is responsible by herself for re-naming the compiled
executable(s) to unsuspicious names, and choosing (at compile time) 
likewise unsuspicious names for config file, database, and log (+lock) file. 
.PP
.SH SECURITY
.PP
For security reasons,
.B samhain
will not write log or data files in a directory, remove the lock file, 
or read the configuration file, if any element
in the path is owned or writeable by an untrusted user (including
group-writeable files with untrusted users in the group, and world-writeable
files).
.br
.I root
and the
.I effective
user are always trusted. You can add more users in the configuration file.
.PP
Using a 
.I "numerical host address" 
in the e\-mail address is more secure than 
using the hostname (does not require
DNS lookup).
.PP
If you use a 
.I precompiled
.B samhain 
executable (e.g. from a
binary distribution), in principle a prospective intruder could easily 
obtain a copy of the executable and analyze it in advance. This will
enable her/him to generate fake audit trails and/or generate
a trojan for this particular binary distribution.
.br
For this reason, it is possible for the user to add more key material into 
the binary executable. This is done with the command:
.PP
.BI "samhain " \-\-add\-key=key@/path/to/executable
.PP
This will read the file 
.I /path/to/executable, add the key 
.I key,
which should not contain a '@' (because it has a special meaning, separating
key from path), overwrite any key previously set by this command, and
write the new binary to the location 
.I /path/to/executable.out
(i.e. with .out appended). You should then copy the new binary to the location
of the old one (i.e. overwrite the old one).
.PP
.B Note that using a precompiled samhain executable from a binary
.B package distribution is not recommended unless you add in key material as
.B described here.

.PP
.SH NOTES
.PP
For initializing the key(s), 
.I "/dev/random" 
is used, if available. This is a  
device supplying cryptographically strong
(non-deterministic) random noise. Because it is slow, 
.B samhain
might appear to hang at startup. Doing some random things 
(performing rain dances, spilling coffee, hunting the mouse) might speed up
things. If you do not have
.IR "/dev/random" ,
lots of statistics from 
.BR vmstat (8) 
and the like will be pooled and mixed by a hash function.
.PP
Some hosts might check whether the sender of the mail is valid. 
Use only 
.I "login names" 
for the sender. 
.br
For sending mails, you may need to set a relay host for the sender domain 
in the configuration file.
.PP
.SH BUGS
.PP
Whoever has the original signature key may change the log file and send fake
e\-mails. The signature keys are e\-mailed at program startup 
with a one\-time pad encryption. 
This should be safe against an eavesdropper on the network, 
but not against someone with read access to the binary, 
.I if 
she has caught
the e\-mail.
.PP
.SH FILES
.PP
.I /etc/samhainrc
.br          
.I /usr/local/man/man8/samhain.8
.br          
.I /usr/local/man/man5/samhainrc.5
.br          
.I /var/log/samhain_log
.br          
.I /var/lib/samhain/samhain_file
.br          
.I /var/lib/samhain/samhain.html
.br          
.I /var/run/samhain.pid

.SH SEE ALSO
.PP
.BR samhainrc (5)

.SH AUTHOR
.PP
Rainer Wichmann (http://la\-samhna.de)
.SH BUG REPORTS
.PP
If you find a bug in
.BR samhain ,
please send electronic mail to
.IR support@la\-samhna.de .
Please include your operating system and its revision, the version of
.BR samhain ,
what C compiler you used to compile it, your 'configure' options, and
any information that you deem helpful.
.PP
.SH COPYING PERMISSIONS
.PP
Copyright (\(co) 1999, 2004 Rainer Wichmann
.PP
Permission is granted to make and distribute verbatim copies of
this manual page provided the copyright notice and this permission
notice are preserved on all copies.
.ig
Permission is granted to process this file through troff and print the
results, provided the printed document carries copying permission
notice identical to this one except for the removal of this paragraph
(this paragraph not being relevant to the printed manual page).
..
.PP
Permission is granted to copy and distribute modified versions of this
manual page under the conditions for verbatim copying, provided that
the entire resulting derived work is distributed under the terms of a
permission notice identical to this one.