mignis 0.9.3.post1

Mignis is a semantic based tool for firewall configuration

Mignis
======

Mignis is a semantic based tool for firewall configuration. It is designed to help
writing **iptables rules** using an more **human-readable syntax**,
without restricting iptables functionalities.

The traslation from Mignis syntax into the corresponding iptables ruleset has been
**formally verified** in a paper published in Computer Security Foundations Symposium (CSF), 2014:

- `Mignis: A Semantic Based Tool for Firewall Configuration <http://ieeexplore.ieee.org/abstract/document/6957122/>`_

Requirements
~~~~~~~~~~~~

- Python 2.7 or higher (Python 3.x supported).

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Description
~~~~~~~~~~~

There are many possible ways to write a set of iptables rules for a
specific purpose, we decided to use the following approach:

- define each interface and its corresponding subnet.
- bind the interface to the subnet (on the mangle-prerouting chain).
This allows us to specify interfaces and/or IP addresses
interchangeably (this is for example exploited in the translation of
a masquerade rule).
- give higher priority to deny rules, so that they are placed before
any other abstract firewall rule (this has to be kept in mind when
writing rules).
- use logging rules to analyze mismatched traffic (which will be
dropped).

Rules' ordering is fundamental when writing iptables rules. Our approach
instead allows to write a set of abstract **rules** which are
**order-independent**.

Usage
~~~~~

::

usage: mignis.py [--help] [-F] [-c filename] [-w filename | -e | -q query]
[-d {0,1,2,3}] [-n] [-f]

A semantic based tool for firewall configuration

optional arguments:
--help, -h show this help message and exit
-d {0,1,2,3}, --debug {0,1,2,3}
set debugging output level (0-2)
-n, --dryrun do not execute/write the rules (dryrun)
-f, --force force rule execution or writing

possible actions::
-F, --flush flush iptables ruleset
-c filename, --config filename
read mignis rules from file

options for --config/-c:
-w filename, --write filename
write the rules to file
-e, --execute execute the rules without writing to file
-q query, --query query
perform a query over the configuration (unstable)

Mignis takes a configuration file and generates a series of iptables
rules.

Rules can either be written to a file (in a format parsable by the
``iptables-restore`` command) or directly executed via the ``iptables``
command.

Usage example:

.. code:: bash

./mignis.py -c config/ex_simple.config -w ex_simple.iptables

This will create an *ex\_simple.iptables* file from the
*ex\_simple.config* configuration. To actually use the rules we just
have to execute ``iptables-restore ex_simple.iptables``.

Configuration file example
^^^^^^^^^^^^^^^^^^^^^^^^^^

::

OPTIONS
default_rules yes
logging no

INTERFACES
lan eth0 10.0.0.0/24
ext eth1 0.0.0.0/0
dummy eth2 none ignore
vpn tun0 10.8.0.0/24

ALIASES
mypc 10.0.0.2
router_ext_ip 1.2.3.4
malicious_host 5.6.7.8
host_over_vpn 10.8.0.123
remote_host_1 20.20.20.1
remote_host_2 30.30.30.2
remote_host_3 40.40.40.3
remote_hosts (remote_host_1, remote_host_2, remote_host_3)

FIREWALL
# no restrictions on outgoing connections
local > *

# ssh accessible from the outside
* > local:22 tcp

# machines inside the lan are NAT'ed (using masquerade) when communicating through ext
lan [.] > ext

# forbid the communication with a malicious host
lan / malicious_host

# dnat to mypc on port 8888
ext > [router_ext_ip:8888] mypc:8888 udp

# dnat to host_over_vpn on port 9999 with masquerade
ext [.] > [router_ext_ip:9999] host_over_vpn:9999 tcp

# allow access to port 80 and 443 on this machine
ext > local:(80, 443) tcp

# allow only a limited set of hosts to access our vpn
remote_hosts > local:1194 udp

POLICIES
* // * icmp
* // * udp
* / *

CUSTOM
# log and accept packets on port 7792
-A INPUT -p tcp --dport 7792 -j LOG --log-prefix "PORT 7792 "
-A INPUT -p tcp --dport 7792 -j ACCEPT

Each configuration file needs 6 sections:

- **OPTIONS**: at the moment two generic mignis options can be
specified:

- ``default_rules`` is used to choose whether to insert default
rules or not. Default rules are usually safe to use and are
hardcoded into mignis and concern broadcast/multicast packets,
invalid packets drops and localhost loopback communication.
- ``logging`` is used to choose whether to log unexplicitly dropped
packets or not (i.e. packets which don't match any rule and get
dropped by the default policy).

- **INTERFACES**: defines each interface with their alias (which can be
used when writing rules). The syntax is
``alias interface-name subnet options``. If the interface doesn't
have an ip address the keyword ``none`` must be used in place of the
subnet. At the moment the only option allowed is ``ignore``, which is
used to tell mignis to always allow traffic on that interface (i.e.
it is not taken into account in firewall rules).
- **ALIASES**: defines aliases for IP addresses. The syntax is
``alias ip-address``.
- **FIREWALL**: contains abstract rules. The syntax is
``abstract-rule | iptables-filters``.

First we define an *address*, which is either an interface, an alias
or an IP address.

An *abstract rule* is defined as follows:
``from [source_nat] opt [dest_nat] to``

- *from* and *to* are addresses,
- *source\_nat* is the address *from* will be SNAT'ed to (it's
possible to use "." to indicate a masquerade),
- *dest\_nat* is the address *to* will be DNAT'ed to,
- *opt* is one of: "/" (deny with DROP), "//" (deny with REJECT),
">" (one-way forward), "<>" (two-way forward)

Finally an *iptables filter* is any iptables option used for
filtering packets. Common options may be "--icmp-type echo-reply",
"-m module", etc.

- **POLICIES**: the default mignis behavior for unmatched packets is to
drop them. This section is useful if one wants to reject packets
instead, using the mignis syntax for rules matching (only drop or
reject rules can be specified). In the example we are rejecting icmp
and udp packets, while we're dropping the rest (this last rule may be
omitted, we wrote it there only for clarity).

- **CUSTOM**: contains raw iptables rules. Note that you can also
modify the tool's behavior here, since you can use the *-D* and *-I*
switches for deleting and inserting rules in specific locations. We
provide this section to add more flexibility, but we cannot guarantee
that your custom rules will not conflict with the abstract ones, so
please use this section with care and only if you know what you're
doing.

Firewall rules examples
^^^^^^^^^^^^^^^^^^^^^^^

Let's see some examples from the configuration above, to clearify how
rules can be written and to see how they're translated into iptables
rules.

1. ``* > local:22 tcp``\ Allows *ssh* (tcp port 22) connections
towards localhost from any interface.

::

iptables -A INPUT -p tcp --dport 22 -j ACCEPT

2. ``lan [.] > ext``\ Allows packets originating from the *lan*
interface to go to *ext*, using a source NAT (masquerade).

::

iptables -A FORWARD -i eth0 -o eth1 -j ACCEPT
iptables -t nat -A POSTROUTING -s 10.0.0.0/24 -o eth1 -j MASQUERADE

3. ``lan / malicious_host``\ Forbids the communication from the *lan*
towards a *malicious host*.

::

iptables -A FORWARD -i eth0 -d 5.6.7.8 -j DROP

4. ``ext > [router_ext_ip:8888] mypc:8888 udp``\ UDP packets
originating from *ext* to *router\_ext\_ip* on port 8888, are DNAT'ed
to *mypc* on port 8888.

::

iptables -t mangle -A PREROUTING -p udp -i eth1 -d 10.0.0.2 --dport 8888 -m state --state NEW -j DROP
iptables -A FORWARD -p udp -i eth1 -d 10.0.0.2 --dport 8888 -j ACCEPT
iptables -t nat -A PREROUTING -p udp -i eth1 -d 1.2.3.4 --dport 8888 -j DNAT --to-destination 10.0.0.2:8888

Note: the first mangle rule is used to block packets which are trying
to reach *mypc* bypassing the NAT.

5. ``ext [.] > [router_ext_ip:9999] host_over_vpn:9999 tcp``\ TCP packets
originating from *ext* to *router\_ext\_ip* on port 9999, are DNAT'ed
to *host\_over\_vpn* on port 9999 using a source NAT (masquerade). The masquerade
ensures that answers from *host\_over\_vpn* are routed through the vpn interface.

::

iptables -t mangle -A PREROUTING -p tcp -i eth1 -d 10.8.0.123 --dport 9999 -m state --state NEW -j DROP
iptables -A FORWARD -p tcp -i eth1 -d 10.8.0.123 --dport 9999 -j ACCEPT
iptables -t nat -A POSTROUTING -p tcp -s 0.0.0.0/0 -d 10.8.0.123 --dport 9999 -j MASQUERADE
iptables -t nat -A PREROUTING -p tcp -i eth1 -d 1.2.3.4 --dport 9999 -j DNAT --to-destination 10.8.0.123:9999

Note: the first mangle rule is used to block packets which are trying
to reach *host\_over\_vpn* bypassing the NAT.

6. ``ext > local:(80, 443) tcp``\ Allow access from *ext* to port 80 and 443 on the
local machine.

::

iptables -A INPUT -p tcp -i eth1 --dport 80 -j ACCEPT
iptables -A INPUT -p tcp -i eth1 --dport 443 -j ACCEPT

7. ``remote_hosts > local:1194 udp``\ Only the list of hosts specified in *remote\_hosts* can connect to our VPN.

::

iptables -A INPUT -p udp -s 20.20.20.1 --dport 1194 -j ACCEPT
iptables -A INPUT -p udp -s 30.30.30.2 --dport 1194 -j ACCEPT
iptables -A INPUT -p udp -s 40.40.40.3 --dport 1194 -j ACCEPT


Work in progress features (still unstable)
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

- Lists operations for excluding hosts/lists from a list. For example
if we define a list alias "list1 (eth0, eth1)" and want a rule that
is valid for *list1* except for the host *1.1.1.1* (which belongs to
the interface *eth0*), we can write ``list1/1.1.1.1 > eth2``.
- Improving checks for identifying overlapping rules.
- Rules queries to list all the connections that match a particular
host, this is useful to see all the packets a host can send/receive.
This has to be expanded with lists and rules (exploiting the
overlapping checks).

Future work for Mignis v2
~~~~~~~~~~~~~~~~~~~~~~~~~

- Complete code rewrite with a modular compiler-like design.
- Support multiple firewall languages (iptables, nftables, Cisco, etc.)
- Abstract-level rules optimizations.
- Accept different kinds of configuration files (e.g. JSON, python
scripts) and/or consider a richer language for writing the rules.
- Provide a 2nd-level abstract semantic using security roles.