.TH "stealth" "1" "2005\-2022" "stealth_4\&.03\&.03" "Security Enhancement" .PP .SH "NAME" stealth \- Stealthy File Integrity Scanner .PP .SH "SYNOPSIS" `\(cq\& represents the location of the used Unix Domain Socket\&. .br .PP \fBstealth\fP \-\-daemon \-\-dry\-run \-\-log \-\-logmail .br \-\-max\-size [BKMG] \-\-no\-mail \-\-parse\-policy\-file .br \-\-random\-interval \-\-repeat .br \-\-skip\-files \-\-syslog .br \-\-syslog\-facility \-\-syslog\-priority \-\-syslog\-tag .br \-\-verbosity policy .PP \fBstealth\fP \-\-dry\-run \-\-log \-\-logmail .br \-\-max\-size [BKMG] \-\-no\-mail \-\-parse\-policy\-file .br \-\-random\-interval \-\-repeat .br \-\-run\-command \-\-skip\-files \-\-stdout \-\-syslog .br \-\-syslog\-facility \-\-syslog\-priority \-\-syslog\-tag .br \-\-verbosity policy .PP \fBstealth\fP {\-\-ping,\-\-reload,\-\-rerun,\-\-resume,\-\-suspend,\-\-terminate} .PP \fBstealth\fP \-\-help \-\-version .PP .SH "DESCRIPTION" .PP The name of the \fBstealth\fP program is an acronym of: .RS \fBSSH\-based Trust Enforcement Acquired through a Locally Trusted Host\&.\fP .RE \fBStealth\fP is based on an idea by \fIHans Gankema\fP and \fIKees Visser\fP, both at the Center for Information Technology of the University of Groningen\&. \fIHopko Meijering\fP provided valuable suggestions for improvement\&. .PP \fBStealth\fP\(cq\&s main task is to perform file integrity tests\&. However, the testing itself will leave no sediments on the tested computer\&. Therefore, \fBstealth\fP has \fIstealthy\fP characteristics\&. This is considered an important feature, improving the security (integrity) of the software of computers monitored by \fBstealth\fP\&. .PP Please realize that \fBstealth\fP intends to be just another security tool: other security measures like firewalls, portscanners, intrusion detection systems, dropping unencrypted protocols, etc\&. are usually required to improve the security of a group of computers that are connected to the Internet\&. \fBStealth\fP is a file integrity scanner, and file integrity scanners offer no substitute for those tools (and vv\&.)\&. .PP \fBStealth\fP uses a policy file to determine the actions to perform\&. Each policy file is uniquely associated with a host being monitored\&. This host (called the \fIclient\fP below) trusts the computer on which \fBstealth\fP runs, called the \fImonitor\fP (hence: a \fILocally Trusted Host\fP)\&. The monitor performs tasks (normally file integrity tests) that \fIEnforce\fP the \fITrust\fP we have in the client computer\&. Since almost all integrity tests can be run on the client, one monitor can control many clients, even if the monitor itself uses aged hard\- and software components\&. .PP As the monitor and the client are (i\&.e\&., should be) different computers, the monitor must communicate with the client in a secure fashion\&. This is realized through SSH\&. So, there\(cq\&s another element of `local trust\(cq\& involved here: the client should permit the monitor to set up a secure SSH connection allowing the monitor to access sensitive elements in the client\(cq\&s file system\&. .PP \fBIt is important to ensure that public access to the monitor is prevented\&. No incoming services should be allowed\&. The only access to the monitor should be via its console and the monitor should be placed in a physically secure location\&. Sensitive information of clients are stored in the monitor\(cq\&s file system\&. To access the clients \fBstealth\fP in daemon mode can use a passphrase\-protected ssh\-key, allowing \fBstealth\fP to perform its tasks thereafter\&. This, too, makes it important to prevent the monitor from being accessed by unauthorized persons\&.\fP .PP If, instead of running \fBstealth\fP in daemon mode it is preferred to let \fBstealth\fP perform single, but automated integrity scans, then new \fBssh\fP(1) connections may be difficult to establish if the used ssh\-key is passphrase\-protected\&. To implement this scenario (i\&.e\&., automated integrity scans using passphrase protected ssh\-keys) the program \fBssh\-cron\fP(1) can profitably be used\&. .PP \fBStealth\fP\(cq\&s current way of connecting to clients uses a single \fBssh\fP(1) connection, which results in only a single \fBsshd\fP(1) entry in the client\(cq\&s logfiles, which lasts for the duration of \fBstealth\fP\(cq\&s run\&. When using \fBstealth\fP in daemon mode this too minimizes the `footprint\(cq\& \fBstealth\fP has on the client hosts\&. .PP The monitor itself normally only requires two types of outgoing services: \fBSSH\fP to reach its clients, and some mail transport agent (e\&.g\&., \fBsendmail\fP(1)) to forward its outgoing mail to some mail\-hub\&. .PP Here is what happens when \fBstealth\fP running using the first synopsis: .IP o First, the \fIpolicy\fP file is read\&. For each client a policy file is defined, specifying the actions to be performed, and specifying the values of several variables used by \fBstealth\fP\&. .IP .IP o If the command\-line option \-\-daemon is specified, \fBstealth\fP runs as a daemon process, using the Unix Domain Socket () for communication with \fBstealth\fP processes running in IPC mode\&. .IP If access to the Unix Domain Socket defined by Stealth running in daemon mode should be restricted, it can be defined in a directory with is only accessible to the user running Stealth (this will often be the root\-user)\&. .IP When running in daemon mode, \-\-repeat may be specified to rerun the integrity scan every seconds\&. If an integrity scan is being performed when, according to the repeat interval the next integrity scan is due, then the current scan is first completed\&. Once completed, the next integrity scan will be performed after seconds seconds\&. .IP .IP o Next, the monitor opens a command shell on the client using \fBssh\fP(1), and a command shell on the monitor computer itself using \fBsh\fP(1)\&. .IP .IP o Once the command shells are available, commands defined in the policy file are executed in their order of appearance\&. Examples are given below\&. Normally, return values of the programs are tested\&. When return values are to be tested \fBstealth\fP terminates when a non\-zero return value is sensed\&. If this happens, a message stating the reason why \fBstealth\fP terminated is written to the report file (and into the mail sent by \fBstealth\fP)\&. In some cases (e\&.g\&., when the report file could not be written), the message is written to the standard error stream\&. .IP .IP o Very often integrity tests can be controlled using \fBfind\fP(1), calling programs like \fBls\fP(1), \fBsha256sum\fP(1) or its own \-printf method to produce file\-integrity related statistics\&. Most of these programs write file names at the end of generated lines\&. This characteristic is used by one of \fBstealth\fP\(cq\&s internal routines to detect changes in the generated output\&. Such changes could indicate some harmful intent, like an installed \fIroot\-kit\fP\&. .IP .IP o When changes are detected, they are logged in a \fIreport file\fP, to which information is always appended\&. \fBStealth\fP never reduces the report file\(cq\&s size or rewrites its contents\&. When information is added to the report file (beyond a plain time stamp) the newly added information is e\-mailed to a configurable e\-mail address for further (human) processing\&. Usually the e\-mail is sent to the systems manager of the tested client\&. \fBStealth\fP follows the `dark cockpit\(cq\& approach in the sense that no mail is sent when no changes were detected\&. .IP .IP o Report and other log\-files may safely be rotated between a pair of \-\-suppress and \-\-resume commands (see below at the section `REPORT FILE ROTATION\(cq\&)\&. .PP If \fBstealth\fP should not be run as a daemon process the second synopsis can be used\&. In this case \fBstealth\fP performs one or more integrity scans (the latter when the \-\-repreat option was specified)\&. When a single integrity scan is requested \fBstealth\fP terminates after the scan\&. When \-\-repeat is specified \fBstealth\fP shows a prompt (i\&.e\&., `? \(cq\&) and terminates after pressing the Enter\-key\&. .PP The third synopsis is used for communication with a \fBstealth\fP daemon\&. In this case the the Unix Domain Socket defined by the \fBstealth\fP daemon process must be specified after the option specifying the requested command\&. .PP .SH "OPTIONS" .PP Short options are provided between parentheses, immediately following their long option equivalents\&. .PP Option descriptions showing (C) can only be used on the command\-line, and are ignored when specified in the second section of the policy file\&. .PP In the overview of options `\(cq\& represents the name of the \fIUnix Domain Socket\fP to use, and `\(cq\& refers to a (relative or absolute) specification of a file location\&. .PP With the first and second synopses relative locations (of the Unix Domain Socket and of other file\-specifications) are interpreted relative to the current working directory\&. .PP Command\-line options overrule options defined in the policy\-file\&. .PP .IP o \-\-daemon (\-d) : (C) run as background (daemon) process\&. When the Stealth daemon process is started, the Unix Domain Socket (tt) may not already exist\&. .IP o \-\-dry\-run: (C) no integrity scans or reloads are performed, but are assumed OK\&. Remaining tasks are normally performed; .IP o \-\-help (\-h): (C) Display help information and exit; .IP o \-\-log (\-L) : log messages are appended to `file\-spec\(cq\&\&. If file\-spec does not exist, it is first created; .IP o \-\-logmail: mail sent by \fBstealth\fP is logged (requires \-\-log or \-\-syslog); .IP o \-\-max\-size [BKMG]: files retrieved by GET commands may at most have bytes (B), KBytes (K), MBytes (M), GBytes (G)\&. The default size is 10M, the default unit is B\&. .IP o \-\-no\-mail: mail is not sent\&. By default mail is sent as configured in the policy\-file (\-\-logmail can be specified independently from \-\-no\-mail); .IP o \-\-parse\-policy\-file (\-p): (C) parse the policy file, after which \fBstealth\fP ends\&. .br Specify once to see the numbered commands; .br twice to see the policy file parsing steps as well\&. .br Results are written to the std\&. output\&. .IP o \-\-ping : (C) performs no actions, but is used to verify that a \fBstealth\fP daemon can be reached via its Unix Domain Socket ()\&. The daemon will respond even if it\(cq\&s currently performing an integrity scan\&. It is used by the /usr/bin/stealthcron script to verify that a \fBstealth\fP daemon is alive\&. .IP o \-\-random\-interval (\-i) [m]>: start the scan a random interval of seconds (or minutes if an `m\(cq\& is appended (no blanks) to ) following the delay specified at \-\-repeat (see below)\&. This option requires specification of the \-\-repeat and \-\-daemon options; .IP o \-\-reload : (C) reloads the configuration and skip\-files and restarts the scan of the \fBstealth\fP daemon process\&. Options defined in the policy file are also reloaded\&. However, command\-line options always take priority over options defined in the policy file, so when command\-line options were used when starting \fBstealth\fP in daemon mode, they cannot be modified by reloading the policy file\&. .IP o \-\-repeat : wake up and perform an integrity scan at interrupts or after seconds (or minutes if an `m\(cq\& is appended (no blanks) to ) after completing the previous integrity scan\&. The option \-\-random\-interval can be used to add a random delay to until the next integrity scan is performed\&. This option requires specification of the and \-\-daemon option; .IP o \-\-rerun : (C) start executing the integrity scan commands that are specified in the \fBstealth\fP daemon process\(cq\&s policy file; .IP o \-\-resume : (C) resume a suspended \fBstealth\fP process, implies \-\-rerun; .IP o \-\-run\-command (\-r) : (C) Only execute command number (natural number)\&. Command numbers are shown by \fBstealth\fP \-\-\-parse\-policy\-file\&. This option can only be specified using the second synopsis; .IP o \-\-skip\-files (\-s) : all entries in are skipped\&. Their integrity is not monitored\&. If an entry is already present in a log file then \fBstealth\fP once generates an IGNORING message in the mail sent to the address specified at EMAIL in the policy file\&. Each entry mentioned in file\-spec must be on a line of its own and must be specified using absolute file paths\&. Entries ending in a slash are assumed to be directories whose full contents must be skipped\&. Other entries are interpreted as the names of files to skip\&. Initial and trailing blanks, empty lines and lines having a # as their 1st non blank character are ignored\&. Here are some examples: .nf # skip all files in user\(cq\&s Mail directory /home/user/Mail/ # skip user\(cq\&s \&.history file /home/user/\&.history .fi .IP o \-\-stdout (\-o): messages are (also) written to the std\&. output stream (only available with the second synopsis); .IP o \-\-suspend : (C) suspends a currently active \fBstealth\fP process\&. Following \-\-suspend use \-\-resume to re\-activate an \fBstealth\fP daemon or \-\-terminate to end an \fBstealth\fP daemon; .IP o \-\-syslog: write syslog messages; .IP o \-\-syslog\-facility : syslog facility to use\&. By default facility DAEMON is used; .IP o \-\-syslog\-priority : syslog priority to use\&. By default priority NOTICE is used; .IP o \-\-syslog\-tag : specifies the identifier that is prefixed to syslog messages\&. By default the tag `STEALTH\(cq\& is used, see also the next section; .IP o \-\-terminate : (C) terminate a currently active \fBstealth\fP process; .IP o \-\-time\-stamp (\-t) : the time\-stamps to use\&. By default UTC\&. To use the local time specify \-\-time\-stamp LT\&. The \-\-time\-stamp option does not apply to time\-stamps generated by syslog (see also the next section); .IP o \-\-usage: (C) Display help information and exit; .IP o \-\-verbosity : determines the amount of logged information\&. Requires options \-\-log or \-\-syslog\&. Possible values are: .br 0: nothing is logged .br 1: (default) mode reports and policy commands .br 2: also: ipc commands and actions .br 3: also: integrity scan informative messages .IP o \-\-version (\-v): (C) Display \fBstealth\fP\(cq\&s version information and terminate; .PP .IP o policy: file specification of the policy file\&. If a relative location is specified then this location is interpreted relative to the current working directory\&. \fBStealth\fP converts this relative specification to an absolute file location, and an option like \-\-reload will reload the policy file from the thus determined absolute file path\&. .PP Only one of the options \-\-daemon, \-\-reload, \-\-resume, \-\-suspend or \-\-terminate can be specified\&. The options \-\-reload, \-\-rerun, \-\-resume, \-\-suspend, and \-\-terminate ignore any other options\&. .PP The following options are still recognized for backward compatibility with \fBstealth\fP pre\-3\&.00 versions and will be removed in a future \fBstealth\fP version\&. They generate error messages suggesting alternatives: .PP .IP o \-\-echo\-commands (\-e): echo commands to std error when they are processed; use \-\-log instead\&. .IP o \-\-keep\-alive: run as a daemon; use \-\-daemon instead\&. .IP o \-\-only\-stdout: scan report is written to stdout; use \-\-stdout instead\&. .IP o \-\-quiet (\-q): suppresses progress messages written to stderr; use \-\-verbosity 0 instead\&. .IP o \-\-suppress : suppresses a currently active \fBstealth\fP process; use \-\-suspend instead\&. .PP The following options were discontinued starting since \fBstealth\fP version 3\&.00\&.00: .IP o \-\-debug (option \-\-verbosity or \-\-dry\-run could be used instead); .IP o \-\-no\-child\-processes; .IP o \-\-parse\-config\-file\&. .PP When specifying long options in policy files initial hyphens should be omitted\&. Here are some examples: .nf %% log /tmp/stealth\&.log verbosity 3 .fi .PP .SH "EXIT STATUS" .PP When requesting an IPC command or when starting \fBstealth\fP as a daemon 0 is returned if the command was successfully completed\&. Otherwise a non\-0 value is returned\&. .PP .SH "OPEN SSH LINK TO CLIENTS" .PP Once \fBstealth\fP has started as a foreground or daemon process performing file integrity scans \fBssh\fP(1) is used to connect to the client(s) monitored by \fBstealth\fP\&. While \fBstealth\fP runs only one \fBssh\fP(1) connection is opened to each client\&. This connection remains active during \fBstealth\fP\(cq\&s lifetime to minimize the number of \fBsshd\fP entries in the client\(cq\&s log files\&. .PP .SH "THE POLICY FILE" .PP The policy file consists of two sections, the second section is optional, and starts at a line merely containing %%\&. .PP The policy file\(cq\&s first section consists of two sets of data: \fIuse directives\fP (starting with the keyword \fBUSE\fP) and \fIcommands\fP\&. Blank lines and information beyond hash\-marks (#) are ignored, while lines following lines terminating in backslashes (\e) are concatenated (\fIen passant\fP removing these trailing backslashes)\&. Leading white space on lines of the policy file is ignored\&. .PP The (optional) second section starts at a line merely containing %%\&. Following this separating line several long option specifications can be entered (see below at section \fBOPTIONS\fP)\&. Options specified on the command\-line take priority over options specified in the policy file\&. Although the \-\-reload option reloads the policy file, it will not change option values originally specified as command\-line options\&. This section may contain specifications of the skip\-files and log options\&. Relative file locations specified for these options are interpreted relative to the location of the policy file\&. E\&.g\&., if the policy file argument is specified as /root/client/policy then the specification log: client\&.log results in \fBstealth\fP writing its logs into the file /root/client/client\&.log\&. .PP .SH "DEFINE DIRECTIVES" .PP \fBDEFINE\fP directives are used to associate longer strings of text with certain symbols\&. E\&.g\&., after DEFINE FINDARGS \-xdev \-type f \-exec /usr/bin/sha256sum {} \e; the specification ${FINDARGS} may be used in \fBUSE DIRECTIVES\fP and \fBcommands\fP (see below) to use the text associated with the \fBFINDARGS\fP symbol\&. .PP Note that \fBDEFINE\fP symbols may also be used in the definition of other \fBDEFINE\fP symbols as well\&. Direct or indirect circular definitions should be avoided, as they are either not or incompletely expanded\&. .PP .SH "USE DIRECTIVES" .PP The following \fBUSE\fP directives may be specified (directives are written in capitals, and should appear exactly as written below: letter casing is preserved)\&. Specifications in angular brackets (like ) represent specifications to be provided by \fBstealth\fP\(cq\&s users: .IP o \fBUSE BASE\fP .br \fBBASE\fP defines the directory from where \fBstealth\fP operates\&. All subsequent relative path specifications in the policy file (including relative path specifications in the policy\(cq\&s second part) are interpreted relative to \fBBASE\fP\&. \fIBy default\fP this is the directory where \fBstealth\fP was started\&. .br \fBBASE\fP and other non\-existing paths are created automatically by \fBstealth\fP if not yet existing\&. .br Example: .br USE BASE /root/client .IP .IP o \fBUSE DD\fP
.br The \fBDD\fP specification uses /bin/dd as default, and defines the location of the \fBdd\fP(1) program, both on the server and on the client\&. The \fBDD\fP program is used to copy files between the client and the monitor over the existing ssh\-connection\&. The program specified here is only used by \fBstealth\fP when executing PUT and GET commands (described below)\&. .br Example showing the default: .br USE DD /bin/dd .IP .IP o \fBUSE DIFF\fP .br The default \fBDIFF\fP specification uses /usr/bin/diff, and defines the location of the \fBdiff\fP(1) program on the monitor\&. The \fBdiff\fP(1) program is used to compare a formerly created logfile of an integrity check with a newly created logfile\&. .br Example showing the default: .br USE DIFF /usr/bin/diff .IP .IP o \fBUSE DIFFPREFIX\fP .br The \fBDIFFPREFIX\fP specification defines the size of the prefix added by the DIFF command to lines produced by commands executed through \fBstealth\fP\&. .IP The default /usr/bin/diff program prefixes lines by either `> \(cq\& or `< \(cq\&\&. The default value for is therefore equal to 2\&. .br Example showing the default: .br USE DIFFPREFIX 2 .IP .IP o \fBUSE EMAIL\fP
.br The \fBEMAIL\fP specification defines the email\-address to receive the report of the integrity scan of the client\&. The `dark cockpit\(cq\& philosophy is followed here: mail is only sent when a modification is detected\&. .br Example showing the default (apparently an email address on the monitor): .br USE EMAIL root .IP .IP o \fBUSE MAILER\fP .br The \fBMAILER\fP specification defines the program that to send e\-mail to the \fBEMAIL\fP\-address\&. Contrary to \fBDIFF\fP and \fBDD\fP and (see below) \fBSH\fP and \fBSSH\fP, \fBMAILER\fP is run as a /bin/sh command, to allow shell\-scripts to process the mail too\&. By default \fBMAILER\fP is defined as \fB/usr/bin/mail\fP\&. \fBMAILER\fP is called with the following arguments: .br \-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\- .br \fBMAILARGS\fP, see below; .br \fBEMAIL\fP, the addressee of the mail\&. .br \-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\- .br Example showing the default: .br USE MAILER /usr/bin/mail .IP As an alternative, the script stealthmail is provided\&. It offers a convenient filter sorting \fBstealth\fP\(cq\&s output and keeping only lines containing the text ADDED, MODIFIED, REMOVED or STEALTH\&. Usually these lines are the ones system managers are interested in\&. The report and log files can always be consulted to determine the actual nature of the changes\&. .IP .IP o \fBUSE MAILARGS\fP .br The \fBMAILARGS\fP specification defines the arguments that are passed to MAILER, followed by the EMAIL specification\&. .br Example showing the default: .br USE MAILARGS \-s \(dq\&STEALTH scan report\(dq\& .br Note that blanks may be used in the subject specification: use double or single quotes to define elements containing blanks\&. Use \e\(dq\& to use a double quote in a string that itself is delimted by double quotes; use \e\(cq\& to use a single quote in a string that itself is delimted by single quotes\&. .IP .IP o \fBUSE REPORT\fP .br \fBREPORT\fP defines the name of the reportfile\&. Information is always appended to this file\&. At each \fBstealth\fP integrity scan a \fItime marker line\fP is written to the report file\&. Only when (in addition to the marker line) additional information is appended to the report file the added contents of the report file are mailed to the mail address specified in the \fBUSE EMAIL\fP specification\&. When a relative file specification is used it is interpreted a location relative to the USE BASE specification\&. .br Example showing the default: .br USE REPORT report .IP .IP o \fBUSE SH\fP .br The \fBSH\fP specification uses /bin/sh as default, and defines the command shell used by the monitor to execute commands on itself\&. This must be an absolute path specification\&. .br Example showing the default: .br USE SH /bin/sh .IP .IP o \fBUSE SSH\fP .br \fBThe SSH specification has no default\fP, and \fImust\fP be specified\&. This must be an absolute path specification\&. .IP Assuming the client \fItrusts\fP the monitor (which is after all what this program is all about, so this should not be a very strong assumption), preferably the public ssh key of the monitor should be placed in the client\(cq\&s root \&.ssh/authorized_keys file, granting the monitor root access to the client\&. Root access is normally needed to gain access to all directories and files of the client\(cq\&s file system\&. .IP In practice, connecting to an account using the \fBsh\fP(1) shell is preferred\&. When another shell is already used by that account, one should make sure that its shell doesn\(cq\&t define its own redirections for standard input and standard output\&. One way to accomplish that is for force the execution of /bin/sh in the \fBUSE SSH\fP specification\&. Examples: .nf # root\(cq\&s shell is /bin/sh: USE SSH root@client \-T \-q # root uses another shell, but the use of /bin/bash is forced: USE SSH root@client \-T \-q exec /bin/bash # an alternative: USE SSH root@client \-T \-q exec /bin/bash \-\-noprofile .fi .PP In some installations \fBstealth\fP is used to inspect the monitor itself, even though this is \fInot\fP recommended, as it breaks one of the main reasons for \fBstealth\fP\(cq\&s existence\&. But in those situations (so, where \fBstealth\fP is used to monitor the integrity of the localhost), /bin/bash could be specified at the USE SSH directive\&. For example: .nf # For stealth inspecting localhost: USE SSH /bin/bash \-\-noprofile .fi .PP .SH "COMMANDS" .PP Following the \fBUSE\fP specifications, \fIcommands\fP can be specified\&. The commands are executed in their order of appearance in the policy file\&. Processing continues until the last command has been processed or until a tested command (see below) returns a non\-zero return value\&. .PP .SH "LABEL COMMANDS" .PP The following \fBLABEL\fP commands are available: .IP o \fBLABEL\fP .br This defines a text\-label which is written to the \fBREPORT\fP file, in front of the output generated by the next \fBCHECK\fP\-command\&. If the next \fBCHECK\fP\-command generates no output, the text\-label is not written to the \fBREPORT\fP\-file\&. Once a \fBLABEL\fP has been defined, it is used until it is redefined by the next \fBLABEL\fP\&. Use an empty \fBLABEL\fP specification to suppress the printing of labels\&. .IP The text may contain \en characters (two characters) which are transformed to a newline character\&. .IP Example: .br LABEL Inspecting files in /etc\enIncluding subdirectories .br LABEL .br (In this example the former \fBLABEL\fP specification is erased by the latter \fBLABEL\fP command)\&. .PP .SH "LOCAL COMMANDS" .PP \fBLOCAL\fP commands are executed on the monitor itself: .IP o \fBLOCAL\fP .br Execute command on the monitor, using the \fBSH\fP command shell\&. The command must succeed (i\&.e\&., must return a zero exit value)\&. .br Example: .br LOCAL scp rootsh@client:/usr/bin/sha256sum /tmp .br This command copies the client\(cq\&s \fBsha256sum\fP(1) program to the monitor\&. .IP .IP o \fBLOCAL NOTEST\fP .br Execute command on the monitor, using the \fBSH\fP command shell\&. The command may or may not succeed\&. .br Example: .br LOCAL NOTEST mkdir /tmp/subdir .br This command creates /tmp/subdir on the monitor\&. The command fails if the directory cannot be created, but this does not terminate \fBstealth\fP\&. .IP .IP o \fBLOCAL CHECK\fP [\fBLOG =\fP] [pathOffset] .br Execute command on the monitor, using the \fBSH\fP command shell\&. The command must succeed\&. The output of this command is compared to the output of this command generated during the previous integrity check run by \fBstealth\fP\&. .IP The phrase \fBLOG =\fP is optional\&. When a relative file location is specified at it is interpreted relatively to the USE BASE path specification\&. .IP PathOffset is also optional\&. If specified it defines the (0\-based) offset where path\-names of inspected files start in lines produced by \&. By default \fBstealth\fP assumes that the first occurrence of a forward slash defines the first character of the path\-names of inspected files\&. .IP For example, if diff\-output looks like this: .nf 01234567890123456789012345678901234567890 (column offsets) 33c33 < 90d8b506d249634c4ff80b9018644567 filename\-specification \-\-\- > b88d0b77db74cc4a742d7bc26cdd2a1e filename\-specification .fi then the specification .nf LOCAL CHECK logfile 36 command\-to\-be\-executed .fi informs \fBstealth\fP where to find the filename specifications in the diff\-output\&. Using the standard /usr/bin/diff command, this offset equals 2 + the offset of the filename\-specification found in command\-to\-be\-executed\&. .IP Any differences between the previous and current output are written to \fBREPORT\fP\&. If differences were found, the existing logfile name is renamed to logfile\&.YYMMDD\-HHMMSS, with YYMMDD\-HHMMSS the (UTC) datetime\-stamp at the time \fBstealth\fP was run\&. .IP Note that eventually many logfile\&.YYMMDD\-HHMMSS files could be created: It is up to the monitor\(cq\&s systems manager to decide what to do with old datetime\-stamped logfiles\&. .IP The logfile specifications may use relative and absolute paths\&. When relative paths are used, these paths are relative to \fBBASE\fP\&. When the directories implied by the logfile specifications do not yet exist, they are created first\&. .IP Example: .br LOCAL CHECK LOG = local/sha256sum sha256sum /tmp/sha256sum .br This command checks the SHA256 sum of the /tmp/sha256sum program\&. The resulting output is saved at \fBBASE\fP/local/sha256sum\&. The program must succeed (i\&.e\&., sha256sum must return a zero exit\-value)\&. .IP .IP o \fBLOCAL NOTEST CHECK\fP [pathOffset] .br Execute command on the monitor, using the \fBSH\fP command shell\&. The command may or may not succeed\&. Otherwise, the command performs exactly like the \fBLOCAL CHECK \&.\&.\&.\fP command, discussed above\&. .IP Example: .br LOCAL NOTEST CHECK LOG=local/sha256sum sha256sum /tmp/sha256sum .br This command checks the SHA256 sum of the /tmp/sha256sum program\&. The resulting output is saved at \fBBASE\fP/local/sha256sum\&. The program must succeed (i\&.e\&., sha256sum must return a zero exit\-value)\&. .PP Note that the \fBscp\fP(1) command can be used to copy files between the client and the monitor, using a local command\&. This, however, is discouraged, as a separate \fBssh\fP(1)\-connection is required for each separate \fBscp\fP(1) command\&. This subtlety was brought to the author\(cq\&s attention by Hopko Meijerink (h\&.meijering@rug\&.nl)\&. .PP To copy files between the client and the monitor, the GET and PUT commands (described below) should be used instead, as these commands use the existing \fBssh\fP(1) connection\&. In general, LOCAL commands should not be used to establish additional \fBssh\fP(1) connections to a client\&. .PP .SH "REMOTE COMMANDS" .PP Remote commands are commands executed on the client using the \fBSSH\fP shell\&. These commands are executed using the standard PATH set for the \fBSSH\fP shell\&. However, it is advised to specify the full pathname to the programs to be executed, to prevent ``trojan approaches\(cq\&\(cq\& where a trojan horse is installed in an `earlier\(cq\& directory of the PATH\-specification than the intended program\&. .PP Two special remote commands are GET and PUT, which can be used to copy files between the client and the monitor\&. Internally, GET and PUT use the DD specification\&. If a non\-default specification is used, one should ensure that the alternate program accepts \fBdd\fP(1)\(cq\&s if=, of=, bs= and count= options\&. With GET the options bs=, count= and of= are used, with PUT the options bs=, count= and if= are used\&. Normally there should be no need to alter the default DD specification\&. .PP The GET command may be used as follows: .IP o \fBGET\fP .br Copy the file indicated by client\-path at the client to local\-path at the monitor\&. Here, client\-path must be the full path of an existing file on the client, local\-path may either be a local directory, in which case the client\(cq\&s file name is used, or another file name may be specified, in which case the client\(cq\&s file is copied to the specified local filename\&. If the local file already exists, it is overwritten by the copy\-procedure\&. .IP Example: .br GET /usr/bin/sha256sum /tmp .br The program /usr/bin/sha256sum, available at the client, is copied to the monitor\(cq\&s /tmp directory\&. If, for whatever reason, copying fails, then \fBstealth\fP terminates\&. .IP .IP o \fBGET NOTEST\fP .br Copy the file indicated by client\-path at the client to local\-path at the monitor\&. Again, client\-path must be the full path of an existing file on the client, local\-path may either be a local directory, in which case the client\(cq\&s file name is used, or another file name may be specified, in which case the client\(cq\&s file is copied to the specified local filename\&. If the local file already exists, it is overwritten by the copy\-procedure\&. .IP Example: .br GET NOTEST /usr/bin/sha256sum /tmp .br The program /usr/bin/sha256sum, available at the client, is copied to the monitor\(cq\&s /tmp directory\&. Remaining commands in the policy file are executed, even if the copying process wasn\(cq\&t successful\&. .PP The PUT command may be used as follows: .IP o \fBPUT\fP .br Copy the file indicated by local\-path at the monitor to remote\-path at the client\&. The argument local\-path must be the full path of an existing file on the monitor\&. The argument remote\-path must be the full path to a file on the client\&. If the remote file already exists, it is overwritten by PUT\&. .IP Example: .br PUT /tmp/sha256sum /usr/bin/sha256sum .br The program /tmp/sha256sum, available at the monitor, is copied to the client as usr/bin/sha256sum\&. If the copying fails, \fBstealth\fP terminates\&. .IP .IP o \fBPUT NOTEST\fP .br Copy the file indicated by local\-path at the monitor to remote\-path at the client\&. The argument local\-path must be the full path of an existing file on the monitor\&. The argument remote\-path must be the full path to a file on the client\&. If the remote file already exists, it is overwritten by PUT\&. .IP Example: .br PUT NOTEST /tmp/sha256sum /usr/bin/sha256sum .br Copy the file indicated by local\-path at the monitor to remote\-path at the client\&. The argument local\-path must be the full path of an existing file on the monitor\&. The argument remote\-path must be the full path to a file on the client\&. If the remote file already exists, it is overwritten by PUT\&. Remaining commands in the policy file are executed, even if the copying process wasn\(cq\&t successful\&. .PP Plain commands can be executed on the client computer by merely specifying them\&. Of course, this implies that programs on the client which are named, e\&.g\&., LABEL, LOCAL or USE, cannot be executed, since these names are interpreted otherwise by \fBstealth\fP\&. It\(cq\&s unlikely that this restriction presents much of a problem\&.\&.\&.\&. .PP The following commands are available for execution on the client: .IP o .br Execute command\-path on the client using the \fBSSH\fP command shell (it is strongly advised to specify a full path to the command to execute)\&. The command must succeed (i\&.e\&., must return a zero exit value)\&. However, any output generated by the the command is ignored\&. .br Example: .br /usr/bin/find /tmp \-type f \-exec /bin/rm {} \e; .br This command removes all ordinary files in and below the client\(cq\&s /tmp directory\&. .IP .IP o \fBNOTEST\fP .br Execute command\-path on the client, using the \fBSSH\fP command shell\&. The command may or may not succeed\&. .br Example: .br NOTEST /usr/bin/find /tmp \-type f \-exec /bin/rm {} \e; .br Same as the previous command, but this time the exit value of /usr/bin/find is not interpreted\&. .IP .IP o \fBCHECK\fP [\fBLOG =\fP] [pathOffset] .br Execute command\-path on the client, using the \fBSSH\fP command shell\&. .IP The phrase \fBLOG =\fP is optional\&. When a relative file location is specified at it is interpreted relatively to the USE BASE path specification\&. .IP PathOffset is also optional, and has the same meaning as for the LOCAL CHECK command, described above\&. The command must succeed\&. The output of this command is compared to the output of this command generated during the previous run of \fBstealth\fP\&. Any differences are written to \fBREPORT\fP\&. If differences were found, the existing logfile name is renamed to logfile\&.YYMMDD\-HHMMSS, with YYMMDD\-HHMMSS the datetime\-stamp at the time \fBstealth\fP was run\&. .IP Note that the command is executed on the client, but the logfile is kept on the monitor\&. This command represents the core of the method implemented by \fBstealth\fP: there will be no residues of the actions performed by \fBstealth\fP on the client computers\&. .IP Several examples (note the use of the backslash as line continuation characters): .IP CHECK LOG = remote/ls\&.root \e .br /usr/bin/find / \e .br \-xdev \-perm /6111 \-type f \-exec /bin/ls \-l {} \e; .IP All suid/gid/executable files on the same device as the root\-directory (/) on the client computer are listed with their permissions, owner and size information\&. The resulting listing is written on the file \fBBASE\fP/remote/ls\&.root\&. .IP CHECK remote/sha256\&.root \e .br /usr/bin/find / \e .br \-xdev \-perm /6111 \-type f \-exec /usr/bin/sha256sum {} \e; .IP The SHA256 checksums of all suid/gid/executable files on the same device as the root\-directory (/) on the client computer are determined\&. The resulting listing is written on the file \fBBASE\fP/remote/sha256\&.root\&. .IP .IP o \fBNOTEST CHECK\fP [\fBLOG =\fP] [pathOffset] .br Execute command\-path on the client, using the \fBSSH\fP command shell\&. .IP The phrase \fBLOG =\fP is optional\&. When a relative file location is specified at it is interpreted relatively to the USE BASE path specification\&. .IP PathOffset is also optional, and has the same meaning as for the LOCAL CHECK command, described above\&. The command may or may not succeed\&. Otherwise, the program acts identically as the \fBCHECK \&.\&.\&.\fP command, described above\&. .IP Example: .br NOTEST CHECK LOG = remote/sha256\&.root \e .br /usr/bin/find / \e .br \-xdev \-perm /6111 \-type f \-exec /usr/bin/sha256sum {} \e; .IP The SHA256 checksums of all suid/gid/executable files on the same device as the root\-directory (/) on the client computer are determined\&. The resulting listing is written on the file \fBBASE\fP/remote/sha256\&.root\&. \fBstealth\fP does not terminate if the /usr/bin/find program returns a non\-zero exit value\&. .PP The maximum download size (using GET or CHECK) can be specified using the \-\-max\-size option, see below\&. By default this size is set at 10M\&. .PP .SH "REPORT FILE ROTATION" Since \fBstealth\fP only appends information to the report file, the report file\(cq\&s size may eventually become prohibitively large, and log\-rotation may be desirable\&. It is of course possible to issue a \-\-terminate command, rotate the logfiles, and restart \fBstealth\fP, but \fBstealth\fP also offers a facility to temporarily suspend integrity scans performed by a \fBstealth\fP daemon process: .IP o Calling \fBstealth\fP with the option \-\-suspend suspends the daemon\(cq\&s integrity scans\&. If \fBstealth\fP is actually performing a series of integrity scans when \-\-suspend is issued, the currently executing command is first completed after which the \-\-suspend command completes\&. Once the \fBstealth\fP daemon has been suspended, automatic or explicit integrity scan requests are denied, and the daemon can only be instructed to resume its scanning tasks (\fBstealth\fP \-\-resume ) or to terminate (\fBstealth\fP \-\-terminate )\&. .IP .IP o Once `\fBstealth\fP \-\-suspend \(cq\& has returned, the report file may safely be rotated (using, e\&.g\&., \fBlogrotate\fP(1)), and a new (empty) report file may optionally be created by the logrotation process\&. .IP .IP o Once the log\-rotation has been completed, the log\-rotation process should issue the command `\fBstealth\fP \-\-resume \(cq\&\&. This resumes the activities of a suspended \fBstealth\fP daemon process, immediately performing the next integrity scan\&. Following this the \fBstealth\fP daemon is back to its original integrity scanning mode\&. Here is an example of \fBlogrotate\fP(1) specification rotating \fBstealth\fP log\-files: .nf /root/stealth/clienthost/small/report /var/log/stealth/clienthost\-small\&.log { daily rotate 4 compress missingok copytruncate sharedscripts prerotate /usr/bin/stealth \-\-suspend /root/stealth/client/small\&.uds endscript postrotate /usr/bin/stealth \-\-resume /root/stealth/client/small\&.uds endscript } .fi .PP .SH "RELOAD, RERUN AND TERMINATE" .PP Here is what happens when \fBstealth\fP is run using the third synopsis: .PP .IP o When started as \fBstealth\fP \-\-reload , the \fBstealth\fP daemon process reloads its policy file and (if specified) \-\-skip\-files specification file\&. Next the \fBstealth\fP daemon process performs a file integrity scan using the information in the re\-read policy and skip\-files files\&. \fBStealth\fP can reload the (modified) contents of the originally specified policy\- and skip\-files names\&. If another policy and/or skip\-files files must be used another \fBstealth\fP process must be started, for which these new filenames are specified\&. .IP .IP o When started as \fBstealth\fP \-\-rerun , the \fBstealth\fP daemon performs another scan (unless it has been suspended using \fBstealth\fP \-\-suspend )\&. .IP .IP o When started as \fBstealth\fP \-\-terminate , the \fBstealth\fP daemon is terminated\&. .PP .SH "RSYSLOG FILTERING" .PP When using \fBrsyslogd\fP(1) property based filters may be used to filter syslog messages and write them to a file of your choice\&. E\&.g\&., to filter messages starting with the syslog message tag (e\&.g\&., STEALTH) use .nf :syslogtag, isequal, \(dq\&STEALTH:\(dq\& /var/log/stealth\&.log :syslogtag, isequal, \(dq\&STEALTH:\(dq\& stop .fi Note that the colon is part of the tag, but is not specified with the syslog\-tag option\&. .PP This causes all messages having the STEALTH: tag to be written on /var/log/stealth\&.log after which they are discarded\&. More extensive filtering is also supported, see, e\&.g\&., http://www\&.rsyslog\&.com/doc/rsyslog_conf_filter\&.html and http://www\&.rsyslog\&.com/doc/property_replacer\&.html .PP Time stamps written by rsyslogd are not controlled by \fBstealth\fP\(cq\&s \-\-time\-stamp option, but, e\&.g\&., by a TZ specification in /etc/default/rsyslog\&. Simply add the line .nf export TZ=UTC .fi to /etc/default/rsyslog, followed by restarting rsyslogd configures rsyslogd to generate time stamps using UTC\&. .PP .SH "DEPLOYMENT SUMMARY" The following summarizes the advised steps to perform when installing stealth\&. All these steps are elaborated upon in \fBstealth\fP\(cq\&s \fIUser Guide\fP (chapter \fIRunning `stealth\(cq\&\fP): .IP o Install \fBstealth\fP (e\&.g\&., use \fBdpkg\fP(1) to install the \fB\&.deb\fP file); .IP o Construct one or more policy files; .IP o Automate (re)starting \fBstealth\fP using \fBcron\fP(1) or \fBssh\-cron\fP(1) (possibly calling \fBstealthcron\fP); .IP o Set up automated log\-file rotation, using, e\&.g\&., \fBstealthcleanup\fP and \fBlogrotate\fP(1), defining one or more /etc/logrotate\&.d/stealth\&.\&.\&. configuration files\&. .PP .SH "FILES" .PP /usr/share/doc/stealth/; .br the policy file; .br files under the \fBBASE\fP directory as defined in the policy file; .br the report file as defined by the policy\(cq\&s \fBUSE REPORT\fP directive\&. .PP .SH "SEE ALSO" \fBcron\fP(1), \fBdd\fP(1), \fBdiff\fP(1), \fBdpkg\fP(1), \fBfind\fP(1), \fBlogrotate\fP(1), \fBls\fP(1), \fBmail\fP(1), \fBsha256sum\fP(1), \fBpasswd\fP(5), \fBrsyslog\fP(1), \fBsendmail\fP(1), \fBsh\fP(1), \fBssh\fP(1), \fBssh\-cron\fP(1) .PP .SH "DIAGNOSTICS" By default, executed commands are echoed to stderr\&. Use \fB\-q\fP to suppress this echoing\&. .PP .SH "BUGS" .PP None reported .PP .SH "COPYRIGHT" This is free software, distributed under the terms of the `GNU General Public License\(cq\&\&. Copyright remains with the author\&. \fBStealth\fP is found at https://fbb\-git\&.gitlab\&.io/stealth/\&. .PP .SH "ORGANIZATION" University of Groningen\&. .PP .SH "AUTHOR" Frank B\&. Brokken (\fBf\&.b\&.brokken@rug\&.nl\fP)\&.