| SAMHAIN(8) | Samhain manual | SAMHAIN(8) |
samhain - check file integrity
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]
samhain [ -p threshold ] { --verify-database=database }
samhain [ -p threshold ] { --create-database=file-list }
samhain [-a | --full-detail] [--delimited] [--binary] [--list-filter=file] -d file| --list-database=file
samhain [-j | --just-list] -L logfile| --verify-log=logfile
samhain -M mailbox| --verify-mail=mailbox
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
yule [-q | --qualified] [ --chroot=chrootdir] [-D | --daemon | --foreground] [log-options]
yule [-P password | --password=password]
yule [-G | --gen-password]
[-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]
The information in this man page is not always up to date. The authoritative documentation is the user manual.
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.
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.
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).
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.
samhain [ -p threshold ] --verify-database=database
Check the filesystem against the database given as argument, and exit with an appropriate exit status. The configuration file will not be read.
samhain [ -p threshold ] --create-database=file-list
Initialize a database from the given file list. The configuration file will not be read. The policy used will be ReadOnly. File content will be stored for a file if its path in the list is preceded with a + sign.
samhain [-a | --full-detail] [--delimited] -d file| --list-database=file
List the entries in the file signature database in a ls -l like format.
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.
samhain -M mailbox| --verify-mail=mailbox
Verify the integrity of the email reports from samhain. All reports must be in the same file.
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.
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.
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.
Depending on the compilation options, some logging facilities may not be available in your executable.
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.
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.
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 ...
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.
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.
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.
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.
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.
/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
Rainer Wichmann (http://la-samhna.de)
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.
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.
| 26 June 2015 |