brick in the (fire)wall (Top 10 list for those who run a firewall)
it's almost firewall review time, so it seemed like a good idea
to inflict this stuff on everyone else, so that you can share
in the joy (or misery -- take your choice) of the process.
policies tend to be as varied as the organizations that implement
them, but there are several general guidelines that make the
process a little more structured and help prevent "rule
rot" from setting in too deeply. Most of you probably immediately
understood what rule rot was even if you've never heard the term
before. For the rest of you though: Rule rot is what happens
when new rules, exceptions, objects, etc., are applied to a firewall
without first looking at what is already in place to maintain
a consistent structure. At some point someone realizes that it's
become an unmanageable nightmare.
making the assumption of a GUI interface such as Checkpoint,
Juniper, iPolicy and such. If you are using a Pix, router ACL,
or other text-/console-driven management method, then you'll
have to add comments to the configuration commands in a master
document, and keep everything up to date in the master document
no matter what!.
this to be the Top 10 things to think about when running a firewall.
It's not complete or perfect. But it will save you a lot of time
and trouble if kept up. If rule rot has already crept in, then
start at step 10 and work backwards.
wants the rule? What manager and techie are responsible for it?
In various places, I've implemented a policy that anyone who
wants an exception or new rule needs to provide written approval
(e-mail is fine) from a manager at director level or higher.
This doesn't represent too great an obstacle, but just enough
to keep frivolous requests (and you WILL get frivolous requests)
to a minimum, while not interfering with business.
each rule and accompanying objects (name/IP address, etc.): Get
and maintain the management and technical name and contact. If
possible, put those names in a comment field with the object
in the actual configuration itself. If the rule is unique to
an individual group, then put the contact information in the
rule comment itself.
temporary or test rules (I've seen "temporary" rules
that have been in place for years), put an expiration date in
the comment field in addition to the contact.
like services together. All inbound Web servers should be in
a single group with the relevant ports (usually 80 and/or 443).
non-standard ports without good reason. "I want to make
it less likely for hackers and bots to find my Web page"
is not a good reason. We tell those people that we will be happy
to perform a Nessus vulnerability scan on their server to see
if it meets acceptable minimums. Alternately, we suggest that
they implement user IDs and passwords.
"I need all (65,000-odd) ports open because I have no idea
what's really required" type of requests. For these, you
can create a temporary rule (see #3), and then track the logs
with the services in use to see what is actually needed. Then
go back and tighten it down.
legitimate non-standard port usage, consider grouping the oddball
systems together under a single rule. In one sense, this violates
the principle of allowing no access that is not absolutely necessary.
But, if you check all relevant systems first (port scan them)
and only one responds on TCP/7000 (and the others don't) and
only two others (properly) respond only on port 24555, then you
may able to group them into an "oddball" rule safely.
Just make sure that you recheck all of them every time you add
a new non-standard port.
people will want special inbound access to their desktops. This
sort of request can take the form of Telnet, SSH, Remote Desktop/Terminal
Server, PCAnywhere, GoToMyPC, Mionet, VNC, LapLink, various databases
and probably a whole host of other things. The answer is: "No.
Implement a VPN." By the way, for those of you not familiar
with it, Mionet is a relative newcomer to the scene. It not only
allows remote desktop access, it also allows the user to "share
resources" with those of his or her choosing. If this scenario
doesn't scare you, you haven't spent enough time in security.
By the way, technically speaking, GoToMyPc and Mionet are outbound
applications, but the direction of access is inward.
enterprises simply allow all outbound connections without further
restriction. There is very little reason to do this, and lots
of reasons not to. First off, the overwhelming majority of traffic
these days is HTTP and its partner HTTPS on well-known ports.
If policy permits, you can allow SSH, FTP (active and passive),
POP3 (dubious, as it can bypass anti-virus protections), SMTP
(what's wrong with the regular mail server?), various forms of
IM (Instant Messaging, in the forms of AIM, MSN, Yahoo, et al).
Peer-to-peer (P2P) file sharing? Not on a bet. The college I
help out gets LOTS of e-e-mail from the RIAA (Recording Industry
Association of America), DMCA (Digital Millennium Copyright Association)
and other copyright-protective trade groups who will provide
a polite warning before serving a summons. You don't want your
employer to have a "CNN moment." They are not much
inflicted all of this on you, it's now expected that you will
keep it up. Pick your interval (weekly, monthly, quarterly, semi-annually
or annually), put it in your (common?) calendar application and
review everything. Specifically the following:
every object defined, validate that the contact names, numbers
and e-mail addresses are still valid. Don't just look at them,
call each and every person to make sure they are still part of
your organization, haven't changed roles (promotions, moves,
etc.) and still have responsibility for the object in question.
the same time, verify and validate that the object and/or services
to it still exist and are still needed. You might be surprised
how many firewall holes I've found for servers that died years
ago. Or for departments that got reorganized out of existence.
all temporary/test rules, find out if they are still needed.
the owners of these systems when was the last time the systems
were updated for OS, application, antivirus, etc. Ask for a specific
scheduled Nessus scans, but that's out of the scope of this blog.
all comments reflect the new data. I love to keep copies of configurations
on my system, or a central server, but if we all get hit by a
bus, the only copy of the configuration visible to the rest of
the IT organization is the one sitting on the firewall itself.
And that is where someone new is going to have to start.