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 is available from github here IPTables::Parse.

The latest version can be downloaded here.

NAME

IPTables::Parse - Perl extension for parsing iptables and ip6tables policies

SYNOPSIS

  use IPTables::Parse;

  my %opts = (
      'use_ipv6' => 0,         # can set to 1 to force ip6tables usage
      'ipt_rules_file' => '',  # optional file path from
                               # which to read iptables rules
      'iptout'   => '/tmp/iptables.out',
      'ipterr'   => '/tmp/iptables.err',
      'debug'    => 0,
      'verbose'  => 0
  );

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

  my $rv = 0;

  ### look for default DROP rules in the filter table INPUT chain
  my ($ipt_hr, $rv) = $ipt_obj->default_drop('filter', 'INPUT');
  if ($rv) {
      if (defined $ipt_hr->{'all'}) {
          print "The INPUT chain has a default DROP rule for all protocols.\n";
      } else {
          my $found = 0;
          for my $proto (qw/tcp udp icmp/) {
              if (defined $ipt_hr->{$proto}) {
                  print "The INPUT chain drops $proto by default.\n";
                  $found = 1;
              }
          }
          unless ($found) {
              print "The INPUT chain does not have any default DROP rule.\n";
          }
      }
  } else {
      print "[-] Could not parse $ipt_obj->{'_ipt_bin_name'} policy\n";
  }

  ### look for default LOG rules in the filter table INPUT chain
  ($ipt_hr, $rv) = $ipt_obj->default_log('filter', 'INPUT');
  if ($rv) {
      if (defined $ipt_hr->{'all'}) {
          print "The INPUT chain has a default LOG rule for all protocols.\n";
      } else {
          my $found = 0;
          for my $proto (qw/tcp udp icmp/) {
              if (defined $ipt_hr->{$proto}) {
                  print "The INPUT chain logs $proto by default.\n";
                  $found = 1;
              }
          }
          unless ($found) {
              print "The INPUT chain does not have any default LOG rule.\n";
          }
      }
  } else {
      print "[-] Could not parse $ipt_obj->{'_ipt_bin_name'} policy\n";
  }

  ### print all chains in the filter table
  for my $chain (@{$ipt_obj->list_table_chains('filter')}) {
      print $chain, "\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. Note that the 'firewalld' infrastructure on Fedora21 is also supported through execution of the 'firewall-cmd' binary. By default, the path to iptables is assumed to be '/sbin/iptables', but if the firewall is 'firewalld', then the '/usr/bin/firewall-cmd' is used.

With this module, 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 determine whether or not a default LOG rule exists. Also, you can get a listing of all rules in a chain with each rule parsed into its own hash.

Note that if you initialize the IPTables::Parse object with the 'ipt_rules_file' key, then all parsing routines will open the specified file for iptables rules data. So, you can create this file with a command like 'iptables -t filter -nL -v > ipt.rules', and then initialize the object with IPTables::Parse->new({'ipt_rules_file'=>'ipt.rules'}). Further, if you are running on a system without iptables installed, but you have an iptables policy written to the ipt.rules file, then you can pass in 'skip_ipt_exec_check=>1' in order to analyze the file without having IPTables::Parse check for the iptables binary.

In summary, in addition to the hash keys mentioned above, optional keys that can be passed to new() include '_iptables' (set path to iptables binary), '_firewall_cmd' (set path to 'firewall-cmd' binary for systems with 'firewalld'), '_fwd_args' (set 'firewall-cmd' usage args; defaults to '--direct --passthrough ipv4'), '_ipv6' (set IPv6 mode for ip6tables), '_debug' and '_verbose'.

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. Here is an example of checking whether the second rule in the INPUT chain (array index 1) allows traffic from any IP to TCP port 80:

  $rules_ar = $ipt_obj->chain_rules('filter', 'INPUT);

  if ($rules_ar->[1]->{'src'} eq '0.0.0.0/0'
          and $rules_ar->[1]->{'protocol'} eq 'tcp'
          and $rules_ar->[1]->{'d_port'}   eq '80'
          and $rules_ar->[1]->{'target'}   eq 'ACCEPT') {

      print "traffic accepted to TCP port 80 from anywhere\n";
  }
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) = $ipt_obj->default_log('filter', 'INPUT');
list_table_chains($table)

This function parses the specified table for all chains that are defined within the table. Data is returned as an array reference. For example, if there are no user-defined chains in the 'filter' table, then the returned array reference will contain the strings 'INPUT', 'FORWARD', and 'OUTPUT'.

  for my $chain (@{$ipt_obj->list_table_chains('filter')}) {
      print $chain, "\n";
  }

AUTHOR

Michael Rash, <mbr@cipherdyne.org>

SEE ALSO

The IPTables::Parse module 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 on CPAN and also here:

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

Source control is provided by git:

  https://github.com/mrash/IPTables-Parse.git

CREDITS

Thanks to the following people:

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

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.

VERSION

Version 1.3 (February, 2015)

Copyright (C) 2005-2015 Michael Rash. All rights reserved.

This module is free software. You can redistribute it and/or modify it under the terms of the Artistic License 2.0. More information can be found here: http://www.perl.com/perl/misc/Artistic.html

This program is distributed "as is" in the hope that it will be useful, but without any warranty; without even the implied warranty of merchantability or fitness for a particular purpose.