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 different 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
       several 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 system'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 corporate 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