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SAMHAIN

SAMHAIN

Section: Samhain manual (8) Updated: 07 August 2004
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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.


 

Index

NAME
SYNOPSIS
INITIALIZING, UPDATING, AND CHECKING
LISTING THE DATABASE
VERIFYING AN AUDIT TRAIL
MISCELLANEOUS
SERVER STARTUP
SERVER MISCELLANEOUS
LOG OPTIONS
WARNING
DESCRIPTION
OPTIONS FOR INITIALIZING, UPDATING, AND CHECKING
OPTIONS FOR LISTING THE DATABASE
OPTIONS TO VERIFY AN AUDIT TRAIL
MISCELLANEOUS OPTIONS
SERVER STARTUP OPTIONS
MISCELLANEOUS SERVER OPTIONS
LOGGING OPTIONS
SIGNALS
DATABASE
LOG FILE
EMAIL
CLIENT/SERVER USAGE
STEALTH
SECURITY
NOTES
BUGS
FILES
SEE ALSO
AUTHOR
BUG REPORTS
COPYING PERMISSIONS

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