SCANLOGD(8)						       System Administration						       SCANLOGD(8)

NAME

       scanlogd - detects and logs TCP port scans

SYNOPSIS

       scanlogd

DESCRIPTION

       scanlogd detects port scans and writes one line per scan via the syslog(3) mechanism. If a source address sends multiple packets to differ-
       ent ports in a short time, the event will be logged. The format of the messages is:

       saddr[:sport] to daddr [and others,] ports port[, port...], ..., flags[, TOS TOS][, TTL TTL] @HH:MM:SS

       The fields in square brackets are optional; sport, TOS, and TTL will only be displayed if they were constant during the scan.

       The flags field represents TCP control bits seen in packets coming to the system from the address of the scan. It is a combination of eight
       characters,  with  each	corresponding  to  one	of the six defined and two reserved TCP control bits (see RFC 793). Control bits that were
       always set are encoded with an uppercase letter, and a lowercase letter is used if the bit was always clear. A question	mark  is  used	to
       indicate bits that changed from packet to packet.

INTERFACES

       In  order  to  do  its  job, scanlogd needs a way to obtain raw IP packets that either come to the system scanlogd is running on, or travel
       across a network segment that is directly connected to the system. Current versions of scanlogd can be built with support for one  of  sev-
       eral packet capture interfaces.

       scanlogd is aware of the raw socket interface on Linux, libnids, and libpcap.

       The  use of libpcap alone is discouraged. If you're on a system other than Linux and/or want to monitor the traffic of an entire network at
       once, you should be using libnids in order to handle fragmented IP packets.

COMPILE-TIME DEFAULTS
       At least 7 different privileged or 21 non-privileged ports, or a weighted combination of those, have to be accessed with no longer  than  3
       seconds	between  the accesses to be treated as a scan.	If more than 5 scans are detected within 20 seconds, that event will be logged and
       logging will be stopped temporarily.

       Logging is done with a facility of daemon and a priority level alert.

       scanlogd should be started as root since it needs access to a packet capture interface.	By default, it chroots to /var/empty and  switches
       to running as user scanlogd after the packet capture interface is initialized.

EXIT STATUS

       If the daemon couldn't start up successfully, it will exit with a status of 1.

USAGE

       You're expected to create a dummy user for scanlogd to run as. Make sure you allocate unique UID and GID to the user.

       In most cases, scanlogd should be started from a rc.d script on system startup.

       In /etc/syslog.conf you may use something like:

       daemon.alert   /var/log/alert

SECURITY NOTES

       As  the name indicates, scanlogd only logs port scans.  It does not prevent them.  You will only receive summarized information in the sys-
       tem's log.

       Obviously, the source address of port scans can be spoofed.  Don't take any action against the source of attacks unless other  evidence	is
       available.  Sometimes IP addresses are shared between many people; this is the case for ISP shell servers, dynamic dialup pools, and corpo-
       rate networks behind NAT (masquerading).

BUGS

       Due to the nature of port scans, both false positives (detecting a scan when there isn't one) and false negatives  (not	detecting  a  scan
       when there's one) are possible. In particular, false positives occur when many small files are transferred rapidly with passive mode FTP.

AUTHORS

       Solar Designer <solar at openwall.com>
       Steffen Dettmer <steffen at dett.de> wrote the initial version of this manual page.

SEE ALSO

       syslog(3), syslog.conf(5), libnids(3), pcap(3)
       scanlogd home page: http://www.openwall.com/scanlogd/
       Phrack Magazine, issue 53, article 13

Openwall Project						    2 June 2004 						       SCANLOGD(8)