cipherdyne.org

Michael Rash, Security Researcher



IPTables::Parse CPAN perl module

This page documents the IPTables::Parse module used by the psad and fwsnort, and projects. Source code for the module can be visualized with gitweb here IPTables::Parse.

The latest version can be downloaded here.



NAME

IPTables::Parse - Perl extension for parsing iptables and ip6tables firewall rulesets


SYNOPSIS

  use IPTables::Parse;

  my $ipt_bin = '/sbin/iptables'; # can set this to /sbin/ip6tables

  my %opts = (
      'iptables' => $ipt_bin,
      'iptout'   => '/tmp/iptables.out',
      'ipterr'   => '/tmp/iptables.err',
      'debug'    => 0,
      'verbose'  => 0
  );

  my $ipt_obj = new IPTables::Parse(%opts)
      or die "[*] Could not acquire IPTables::Parse object";

  my $rv = 0;

  my $table = 'filter';
  my $chain = 'INPUT';

  my ($ipt_hr, $rv) = $ipt_obj->default_drop($table, $chain);
  if ($rv) {
      if (defined $ipt_hr->{'all'}) {
          print "The INPUT chain has a default DROP rule for all protocols.\n";
      } else {
          for my $proto (qw/tcp udp icmp/) {
              if (defined $ipt_hr->{$proto}) {
                  print "The INPUT chain drops $proto by default.\n";
              }
          }
      }
  } else {
      print "[-] Could not parse $ipt_obj->{'_ipt_bin_name'} policy\n";
  }

  ($ipt_hr, $rv) = $ipt_obj->default_log($table, $chain);
  if ($rv) {
      if (defined $ipt_hr->{'all'}) {
          print "The INPUT chain has a default LOG rule for all protocols.\n";
      } else {
          for my $proto (qw/tcp udp icmp/) {
              if (defined $ipt_hr->{$proto}) {
                  print "The INPUT chain logs $proto by default.\n";
              }
          }
      }
  } else {
      print "[-] Could not parse $ipt_obj->{'_ipt_bin_name'} policy\n";
  }


DESCRIPTION

The IPTables::Parse package provides an interface to parse iptables or ip6tables rules on Linux systems through the direct execution of iptables/ip6tables commands, or from parsing a file that contains an iptables/ip6tables policy listing. You can get the current policy applied to a table/chain, look for a specific user-defined chain, check for a default DROP policy, or determing whether or not logging rules exist.


FUNCTIONS

The IPTables::Parse extension provides an object interface to the following functions:

chain_policy($table, $chain)

This function returns the policy (e.g. 'DROP', 'ACCEPT', etc.) for the specified table and chain:

  print "INPUT policy: ", $ipt_obj->chain_policy('filter', 'INPUT'), "\n";
chain_rules($table, $chain)

This function parses the specified chain and table and returns an array reference for all rules in the chain. Each element in the array reference is a hash with the following keys (that contain values depending on the rule): src, dst, protocol, s_port, d_port, target, packets, bytes, intf_in, intf_out, to_ip, to_port, state, raw, and extended. The extended element contains the rule output past the protocol information, and the raw element contains the complete rule itself as reported by iptables or ip6tables.

default_drop($table, $chain)

This function parses the running iptables or ip6tables policy in order to determine if the specified chain contains a default DROP rule. Two values are returned, a hash reference whose keys are the protocols that are dropped by default if a global ACCEPT rule has not accepted matching packets first, along with a return value that tells the caller if parsing the iptables or ip6tables policy was successful. Note that if all protocols are dropped by default, then the hash key 'all' will be defined.

  ($ipt_hr, $rv) = $ipt_obj->default_drop('filter', 'INPUT');
default_log($table, $chain)

This function parses the running iptables or ip6tables policy in order to determine if the specified chain contains a default LOG rule. Two values are returned, a hash reference whose keys are the protocols that are logged by default if a global ACCEPT rule has not accepted matching packets first, along with a return value that tells the caller if parsing the iptables or ip6tables policy was successful. Note that if all protocols are logged by default, then the hash key 'all' will be defined. An example invocation is:

  ($ipt_hr, $rv) = $ipt_obj->default_log('filter', 'INPUT');


AUTHOR

Michael Rash, <mbr@cipherdyne.org>


SEE ALSO

The IPTables::Parse is used by the IPTables::ChainMgr extension in support of the psad and fwsnort projects to parse iptables or ip6tables policies (see the psad(8), and fwsnort(8) man pages). As always, the iptables(8) and ip6tables(8) man pages provide the best information on command line execution and theory behind iptables and ip6tables.

Although there is no mailing that is devoted specifically to the IPTables::Parse extension, questions about the extension will be answered on the following lists:

  The psad mailing list: http://lists.sourceforge.net/lists/listinfo/psad-discuss
  The fwsnort mailing list: http://lists.sourceforge.net/lists/listinfo/fwsnort-discuss

The latest version of the IPTables::Parse extension can be found at:

http://www.cipherdyne.org/modules/


CREDITS

Thanks to the following people:

  Franck Joncourt <franck.mail@dthconnex.com>
  Grant Ferley


AUTHOR

The IPTables::Parse extension was written by Michael Rash <mbr@cipherdyne.org> to support the psad and fwsnort projects. Please send email to this address if there are any questions, comments, or bug reports.


COPYRIGHT AND LICENSE

Copyright (C) 2005-2012 by Michael Rash

This library is free software; you can redistribute it and/or modify it under the same terms as Perl itself, either Perl version 5.8.5 or, at your option, any later version of Perl 5 you may have available.