Ubuntu Manpage: portsentry.conf - portsentry's main configuration file

NAME

       portsentry.conf - portsentry's main configuration file

DESCRIPTION

       This manual page documents briefly the format of portsentry's(8) configuration file.

OPTIONS

TCP_PORTS
A comma delimited string of TCP ports you want PortSentry to listen to. This string
can NOT have any spaces in it. You can put in as many sockets as you want.
PortSentry will try to bind them all up until the default limit of 64.

For the stealth scan detection modes, the ports are not "bound" per se, but they
are monitored at the socket level for connections.

For the Advanced Stealth Scan Detection (see below) this list is *ignored*

UDP_PORTS
The same as above, except for UDP ports. You need to be very careful with UDP mode
as an attacker can forge a port sweep and make you block any number of hosts. Use
this option with caution, or not at all if your host is a well-known Internet
connected system.

For the Advanced Stealth Scan Detection (see below) this list is *ignored*

ADVANCED_PORTS_TCP
A number indicating the highest port number to monitor down from. Any port *below*
this number is then monitored. The default is 1024 (reserved port range), but can
be made as large as 65535 (system max). It's recommended going over 1024 with this
option.

ADVANCED_PORTS_UDP
Same as above, except for UDP.

ADVANCED_EXCLUDE_TCP
A comma delimited string of TCP ports that should be manually excluded from
monitoring in Advanced mode. These are normally ports that may get hit by mistake
by remote clients and shouldn't cause alarms (ident, SSL, etc).

ADVANCED_EXCLUDE_UDP
Same as above, except for UDP.

IGNORE_FILE
The path to the file that contains IP addresses of hosts you want to always be
ignored.

BLOCKED_FILE
The path to the file that contains the IP addresses of blocked hosts.

RESOLVE_HOST - This option turns off DNS resolution for
hosts. If you have a slow DNS server it may be more effective to turn off
resolution.

BLOCK_UDP
This option disables all automatic responses to UDP probes. Because UDP can be
easily forged, it may allow an attacker to start a denial of service attack against
the protected host, causing it to block all manner of hosts that should normally be
left alone. Setting this option to "0" will disable all responses, although the
connects are still logged. This option is mainly useful for Internet exposed
hosts. For internal hosts you should leave this enabled. If someone internally is
firing spoofed packets at you, then you have a much bigger problem than a denial of
service.

BLOCK_TCP
Same as above, but for TCP. Packet forgery is not as big a problem though because
PortSentry waits for a full connect to occur and this is much harder to forge in
the basic modes. Leave this enabled, even for Internet connected hosts. For stealth
scan detection modes the UDP warning applies:

An attacker can cause you to block hosts you don't want to through packet
forgery. I wouldn't worry about this until it is a problem, but you should be
aware of it.

KILL_ROUTE
This is the command to run to drop the offending route(see route(8)) if an attack
is detected. This is the *full path* to the route command along with the necessary
parameters to make the command work. The macro $TARGET$ will be substituted with
the attacking host IP and is REQUIRED in this option. Your gateway should be a
*dead host* on the local subnet. On some systems though you can just put in the
localhost address (127.0.0.1) and this will probably work. All packets from the
target host will get routed to this address so don't mess this up. More modern
route commands will include a "-blackhole" or "-reject" flag. Check your man(1)
pages and if your route command supports this feature you should use it (although
it's recommend using packet filtering instead, see below).

Also be aware that this creates what is known as an "asynchronous route" which
basically means packets enter your host via one route and are sent out on another
(dead) route. This works OK for full TCP connect requests, but for UDP and stealth
scan modes it still allows packets to activate PortSentry and you may get a series
of "already blocked" alarms by PortSentry. For UDP scans this method prevents ICMP
messages from returning to the attacker so all ports appear open. However, if the
attacker is performing an actual exploit with UDP the drop route method will not
work. The asynchronous route allows the packet to hit the system and the attacker
could perform a "blind" attack with UDP if they know what the responses are going
to be.

By far the best method is to use the local packet filter (see ipfwadm(8),
ipchains(8), or iptables(8)). This is a much cleaner solution and is detailed in
the config file. The macro $PORT$ will substitute the port that was connected to by
the attacker, but this is NOT required for this option. The macro $MODE$ reports
what mode the blocking occurred in (tcp, udp, stcp, sudp, atcp, audp) but is also
NOT required.

KILL_HOSTS_DENY
This is the format of the string to drop into the hosts.deny file that TCP wrappers
uses(see hosts_access(5), and hosts_options(5)). Again the $TARGET$ macro is
expanded out to be the IP of the attacker and is required. You can also drop in any
TCP wrapper escape codes here as well (%h, twist, etc). The macro $PORT$ will
substitute the port that was connected to by the attacker, but this is NOT required
for this option. The macro $MODE$ reports what mode the blocking occurred in (tcp,
udp, stcp, sudp, atcp, audp) but is also NOT required.

KILL_RUN_CMD
This is a command you want run *before* the route is dropped to the attacker. You
can put in any program/script you want executed when an attack is detected. WE
NEVER RECOMMEND PUTTING IN RETALIATORY ACTION AGAINST AN ATTACKING HOST. Virtually
every time you're are port scanned the host doing the scanning has been compromised
itself. Therefore, if you retaliate you are probably attacking an innocent(?)
party. Also the goal of security is to make the person GO AWAY. You don't want to
irritate them into making a personal vendetta against you. Remember, even a 13
year old can run a [insert favorite D.O.S. program here] attack against you from
their Windows box to make your life miserable. As above, the $TARGET$, $PORT$ and
$MODE$ macros are available to you but they are not required with this option as
above.

KILL_RUN_CMD_FIRST
Setting this to "1" makes the command above run before the route is dropped.
Setting it to "0" makes the command run aftter the blocking has occurred.

SCAN_TRIGGER
PortSentry has a state engine that will remember hosts that connected to it.
Setting this value will tell PortSentry to allow X number of grace port hits before
it reacts. This will detect both sequential and random port sweeps. The default is
0 which will react immediately. A setting of 1 or 2 will reduce false alarms,
anything higher is probably too much as anything more than 3 hits to different
ports is pretty suspicious behavior. Usually you can leave this at 0 without any
consequence, with the exception of Advanced stealth scan detection modes where you
may create a "hair trigger" if you aren't careful. Use your own discretion.

PORT_BANNER
A text banner you want displayed to the connecting host if the PortSentry is
activated. Leave this commented out if you don't want this feature. If you do use
it, try not to taunt the person too badly. It's recommended keeping it professional
and to the point. The banner is *not* displayed when stealth scan detection modes
are used.

AUTHOR

       portsentry was written by Craig H. Howland <crowland@users.sf.net>.

       This  manual  page  is essentially just a "cut and paste" from the README.install file and
       was done by Guido Guenther <agx@debian.org>(hopefully without adding too many errors), for
       the Debian GNU/Linux system (but may be used by others).

                                                                               PORTSENTRY.CONF(5)

NAME

DESCRIPTION

OPTIONS

SEE ALSO

AUTHOR