NAME
samhain - check file integrity
SYNOPSIS
INITIALIZING, UPDATING, AND CHECKING
samhain { -t init|--set-checksum-test=init } [--init2stdout] [-r
DEPTH|--recursion=DEPTH] [log-options]
samhain { -t update|--set-checksum-test=update } [-D | --daemon |
--foreground] [--forever] [-r DEPTH|--recursion=DEPTH] [log-options]
samhain { -t check|--set-checksum-test=check } [-D | --daemon |
--foreground] [--forever] [-r DEPTH,--recursion=DEPTH] [log-options]
LISTING THE DATABASE
samhain [-a | --full-detail] [--delimited] -d file|
--list-database=file
VERIFYING AN AUDIT TRAIL
samhain [-j | --just-list] -L logfile| --verify-log=logfile
samhain -M mailbox| --verify-mail=mailbox
MISCELLANEOUS
samhain --server-port=portnumber
samhain -H string | --hash-string=string
samhain -c | --copyright
samhain -v | --version
samhain -h | --help
samhain -V key@/path/to/executable | --add-key=key@/path/to/executable
SERVER STARTUP
yule [-q | --qualified] [ --chroot=chrootdir] [-D | --daemon |
--foreground] [log-options]
SERVER MISCELLANEOUS
yule [-P password | --password=password]
yule [-G | --gen-password]
LOG OPTIONS
[-s threshold | --set-syslog-severity=threshold] [-l threshold |
--set-log-severity=threshold] [-m threshold |
--set-mail-severity=threshold] [-e threshold |
--set-export-severity=threshold] [-p threshold |
--set-print-severity=threshold] [-x threshold |
--set-external-severity=threshold] [ --set-prelude-severity=threshold]
[ --set-database-severity=threshold] [ --enable-trace] [
--trace-logfile=tracefile]
WARNING
The information in this man page is not always up to date. The
authoritative documentation is the user manual.
DESCRIPTION
samhain is a file integrity / intrusion detection system both for
single hosts and networks. It consists of a monitoring application
(samhain) running on individual hosts, and (optionally) a central log
server (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.
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 (/dev/console if run as daemon). 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.
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.
OPTIONS FOR INITIALIZING, UPDATING, AND CHECKING
samhain -t init, --set-checksum-test=init [options]
Initialize the database of file signatures. The path to the database is
compiled in, and initializing will append to the respective file (or
create it, if it does not exist). It is ok to append to e.g. a JPEG
image, but it is an error to append to an already existing file
signature database.
[--init2stdout]
Write the database to stdout.
[-r DEPTH|--recursion=DEPTH]
Set the (global) recursion depth.
samhain -t update, --set-checksum-test=update [options]
Update the database of file signatures. The path to the database is
compiled in, and updating will overwrite the database, starting from
the start of the database (which may not be identical to the start of
the file - see above).
[-r DEPTH|--recursion=DEPTH]
Set the (global) recursion depth.
[-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.
[--foreground]
Run in the foreground. This will cause samhain to exit after the
update, unless the option --forever is used.
[--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.
samhain -t check, --set-checksum-test=check [options]
Check the filesystem against the database of file signatures. The path
to the database is compiled in.
[-r DEPTH|--recursion=DEPTH]
Set the (global) recursion depth.
[-D|--daemon]
Run as daemon. File checks are performed as specified by the
timing options in the configuration file.
[--foreground]
Run in the foreground. This will cause samhain to exit after the
file check, unless the option --forever is used.
[--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.
OPTIONS FOR LISTING THE DATABASE
samhain [-a | --full-detail] [--delimited] -d file|
--list-database=file
List the entries in the file signature database in a ls -l like format.
[-a | --full-detail]
List all informations for each file, not only those you would
get with ls -l. Must precede the -d option.
[--delimited]
List all informations for each file, in a comma-separated
format. Must precede the -d option.
[--list-file=file]
List the literal content of the given file as stored in the
database. Content is not stored by default, must be enabled in
the runtime configuration file. Must precede the -d option.
OPTIONS TO VERIFY AN AUDIT TRAIL
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.
samhain [-j | --just-list] -L logfile| --verify-log=logfile
Verify the integrity of a signed logfile. The signing key is
auto-generated on startup, and sent by email. 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.
[-j | --just-list]
Just list the logfile, do not verify it. This option must come
first. It is mainly intended for listing the content of an
obfuscated logfile, if samhain is compiled with the stealth
option.
samhain -M mailbox| --verify-mail=mailbox
Verify the integrity of the email reports from samhain. All
reports must be in the same file.
MISCELLANEOUS OPTIONS
samhain --server-port=portnumber
Choose the port on the server host to which the client will connect.
samhain -H string | --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.
samhain -c | --copyright
Print the copyright statement.
samhain -v | --version
Show version and compiled-in options.
samhain -h | --help
Print supported command line options (depending on compilation
options).
samhain -V key@/path/to/executable | --add-key=key@/path/to/executable
See the section "SECURITY" below.
SERVER STARTUP OPTIONS
yule [-q | --qualified] [ --chroot=chrootdir] [-D | --daemon |
--foreground] [log-options]
Start the server, which is named yule by default. If the server is
started with superuser privileges, it will drop them after startup.
[-q | --qualified]
Log client hostnames with fully qualified path. The default is
to log only the leftmost domain label (i.e. the hostname).
[ --chroot=chrootdir] Chroot to the listed directory after
startup.
[-D | --daemon]
Run as daemon.
[--foreground]
Run in the foreground.
MISCELLANEOUS SERVER OPTIONS
yule [-G | --gen-password]
Generate a random 8-byte password and print it out in hexadecimal
notation.
yule [-P password | --password=password]
Use the given password and generate an entry suitable for the [Clients]
section of the configuration file.
LOGGING OPTIONS
Depending on the compilation options, some logging facilities may not
be available in your executable.
-s threshold, --set-syslog-severity=threshold
Set the threshold for logging events via syslogd(8). Possible
values are debug, info, notice, warn, mark, err, crit, alert,
and none. By default, everything equal to and above the
threshold will be logged. Time stamps have the priority warn,
system-level errors have the priority err, and important
start-up messages the priority alert. The signature key for the
log file will never be logged to syslog or the log file itself.
-l threshold, --set-log-severity=threshold
Set the threshold for logging events to the log file.
-m threshold, --set-mail-severity=threshold
Set the threshold for logging events via e-mail.
-e threshold, --set-export-severity=threshold
Set the threshold for forwarding events via TCP to a log server.
-x threshold, --set-extern-severity=threshold
Set the threshold for calling external logging programs/scripts
(if any are defined in the configuration file).
-p threshold, --set-print-severity=threshold
Set the threshold for logging events to stdout. If samhain runs
as a daemon, this is redirected to /dev/console.
--set-prelude-severity=threshold
Set the threshold for logging events to the Prelude IDS.
--set-database-severity=threshold
Set the threshold for logging events to the
MySQL/PostgreSQL/Oracle database.
SIGNALS
SIGUSR1
Switch on/off maximum verbosity for console output.
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 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 same host).
SIGHUP Reread the configuration file.
SIGTERM
Terminate.
SIGQUIT
Terminate after processing all pending requests from clients.
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.
SIGTTOU
Force a file check (only client/standalone, and only in daemon
mode).
DATABASE
The database (default name samhain_file) is a binary file, which can be
created or updated using the -t init or the -t update option. If you
use -t init, you need to remove the old database first, otherwise the
new version will be appended to the old one. The file may be (clear
text) signed by PGP/GnuPG.
It is recommended to use GnuPG with the options gpg -a --clearsign
--not-dash-escaped
samhain will check the signature, if compiled with support for that.
At startup 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.
LOG FILE
Each entry in the log file has the format Severity : [Timestamp]
Message, where the timestamp may be obtained from a time server rather
than from the system clock, if samhain has been compiled with support
for this. Each entry is followed by a signature, which is computed as
Hash(Entry Key_N), and Key_N is computed as 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.
The default name of the log file is samhain_log. To prevent multiple
instances of samhain from writing to the same log file, the log file is
locked by creating a lock file, which is normally deleted at program
termination. The default name of the lock file is samhain.lock. If
samhain is terminated abnormally, i.e. with kill -9, a stale lock file
might remain, but usually samhain will be able to recognize that and
remove the stale lock file on the next startup.
EMAIL
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 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 ...
CLIENT/SERVER USAGE
To monitor several machines, and collecting data by a central log
server, samhain may be compiled as a client/server application. The log
server (yule) will accept connection requests from registered clients
only. With each client, the server will first engage in a
challenge/response protocol for authentication of the client and
establishing a session key.
This protocol requires on the client side a password, and on the server
side a verifier that is computed from the password.
To register a client, simply do the following:
First, with the included utility program 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.
Second, after re-setting the password in the client executable, you can
use the server’s convenience function yule -P 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.
Third, in the configuration file for the server, under the [Clients]
section, enter the suggested registration entry of the form
Client=hostname@salt@verifier, where hostname must be the (fully
qualified) hostname of the machine on which the client will run. Don’t
forget to reload the server configuration thereafter.
If a connection attempt is made, the server will lookup the entry for
the connecting host, and use the corresponding value for the verifier
to engage in the session key exchange. Failure to verify the client’s
response(s) will result in aborting the connection.
STEALTH
samhain may be compiled with support for a 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.
In this mode, the runtime executable will hold no printable strings,
and the configuration file is expected to be a postscript file with
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 convert(1), which is part of the ImageMagick(1)
package, such as: convert +compress ima.jpg ima.ps.
To hide/extract the configuration data within/from the postscript file,
a utility program samhain_stealth is provided. Use it without options
to get help.
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.
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.
SECURITY
For security reasons, 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).
root and the effective user are always trusted. You can add more users
in the configuration file.
Using a numerical host address in the e-mail address is more secure
than using the hostname (does not require DNS lookup).
If you use a precompiled 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.
For this reason, it is possible for the user to add more key material
into the binary executable. This is done with the command:
samhain --add-key=key@/path/to/executable
This will read the file /path/to/executable, add the key 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 /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).
Note that using a precompiled samhain executable from a binary package
distribution is not recommended unless you add in key material as
described here.
NOTES
For initializing the key(s), /dev/random is used, if available. This is
a device supplying cryptographically strong (non-deterministic) random
noise. Because it is slow, 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
/dev/random, lots of statistics from vmstat(8) and the like will be
pooled and mixed by a hash function.
Some hosts might check whether the sender of the mail is valid. Use
only login names for the sender.
For sending mails, you may need to set a relay host for the sender
domain in the configuration file.
BUGS
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,
if she has caught the e-mail.
FILES
/etc/samhainrc
/usr/local/man/man8/samhain.8
/usr/local/man/man5/samhainrc.5
/var/log/samhain_log
/var/lib/samhain/samhain_file
/var/lib/samhain/samhain.html
/var/run/samhain.pid
SEE ALSO
samhainrc(5)
AUTHOR
Rainer Wichmann (http://la-samhna.de)
BUG REPORTS
If you find a bug in samhain, please send electronic mail to
support@la-samhna.de. Please include your operating system and its
revision, the version of samhain, what C compiler you used to compile
it, your ’configure’ options, and any information that you deem
helpful.
COPYING PERMISSIONS
Copyright (©) 1999, 2004 Rainer Wichmann
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.
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.
07 August 2004