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Re: Why does Debian allow all incoming traffic by default

From Roberto C. Sánchez <roberto@debian.org>
Newsgroups linux.debian.user
Subject Re: Why does Debian allow all incoming traffic by default
Date 2018-09-21 05:50 +0200
Message-ID <wAkC5-3lx-1@gated-at.bofh.it> (permalink)
References <wAjZo-39S-1@gated-at.bofh.it> <wAkiJ-3fB-1@gated-at.bofh.it> <wAksp-3ix-1@gated-at.bofh.it>
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On Fri, Sep 21, 2018 at 09:02:26AM +0530, Subhadip Ghosh wrote:
> Hi Roberto,
> 
> On Friday 21 September 2018 08:51 AM, Roberto C. Sánchez wrote:
> > On Fri, Sep 21, 2018 at 08:34:50AM +0530, Subhadip Ghosh wrote:
> > > Hi,
> > > 
> > > I am using Debian and the recently I learned that a standard Debian
> > > installation allows all 3 types of traffics especially incoming by default.
> > What do you mean by "all 3 types of traffics"?
> Incoming, Outgoing and Forward

I see.

Blocking incoming and forwarded traffic would probably not be surprising
to many people.  However, blocking outgoint traffic would be exceedingly
confusing to many people.

> > > I know I can easily use iptables to tighten the rules but I wanted to know
> > > the reasons behind the choice of this default behaviour and if it makes the
> > > system more vulnerable?
> > The behavior you observe is likely because that is the best default that is
> > universally applicable.
> But does it make the system more vulnerable in any way to attacks over the
> network? And how will a new Debian user would know of this behaviour? I
> don't even see it mentioned on the Stretch Installation manual anywhere.

I see.  Perhaps the Debian Administrator's Handbook, Chapter 14 is what
you are looking for:

https://www.debian.org/doc/manuals/debian-handbook/security.en.html

While there is possibly an argument that not configuring a firewall by
default introduces some vulnerability, it is equally valid to argue that
there are no sensible default firewall policies that can be put into
place without a defined threat model.

I suspect that the vast majority of people deploying systems are doing
so behind some sort of device that provides border security to the local
network (e.g., router/firewall/NAT/etc.).  So, if the default threat
model is "a relatively trusted network with adequate border security"
then the current default is appropriate.

Those who deploy systems directly to a location where they are in
immediate contact with the public Internet should already understand the
ramifications of that decision and tailor their installation process
accordingly.

Regards,

-Roberto

-- 
Roberto C. Sánchez

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Thread

Why does Debian allow all incoming traffic by default Subhadip Ghosh <subhadip.sky@gmail.com> - 2018-09-21 05:10 +0200
  Re: Why does Debian allow all incoming traffic by default Roberto C. Sánchez <roberto@debian.org> - 2018-09-21 05:30 +0200
    Re: Why does Debian allow all incoming traffic by default Subhadip Ghosh <subhadip.sky@gmail.com> - 2018-09-21 05:40 +0200
      Re: Why does Debian allow all incoming traffic by default Roberto C. Sánchez <roberto@debian.org> - 2018-09-21 05:50 +0200
        Re: Why does Debian allow all incoming traffic by default deloptes <deloptes@gmail.com> - 2018-09-21 07:10 +0200
        Re: Why does Debian allow all incoming traffic by default Subhadip Ghosh <subhadip.sky@gmail.com> - 2018-09-21 19:40 +0200
      Re: Why does Debian allow all incoming traffic by default Dan Ritter <dsr@randomstring.org> - 2018-09-21 19:10 +0200
        Re: Why does Debian allow all incoming traffic by default Subhadip Ghosh <subhadip.sky@gmail.com> - 2018-09-21 19:40 +0200
          Re: Why does Debian allow all incoming traffic by default deloptes <deloptes@gmail.com> - 2018-09-21 20:00 +0200
            Re: Why does Debian allow all incoming traffic by default Subhadip Ghosh <subhadip.sky@gmail.com> - 2018-09-21 20:10 +0200
              Re: Why does Debian allow all incoming traffic by default Brian <ad44@cityscape.co.uk> - 2018-09-21 21:40 +0200
          Re: Why does Debian allow all incoming traffic by default David Wright <deblis@lionunicorn.co.uk> - 2018-09-21 21:50 +0200
          Re: Why does Debian allow all incoming traffic by default mick crane <mick.crane@gmail.com> - 2018-09-23 01:10 +0200
            Re: Why does Debian allow all incoming traffic by default Brian <ad44@cityscape.co.uk> - 2018-09-23 20:00 +0200
              Re: Why does Debian allow all incoming traffic by default Joe <joe@jretrading.com> - 2018-09-23 23:00 +0200
                Re: Why does Debian allow all incoming traffic by default Brian <ad44@cityscape.co.uk> - 2018-09-24 00:00 +0200
        Re: Why does Debian allow all incoming traffic by default Pascal Hambourg <pascal@plouf.fr.eu.org> - 2018-09-22 09:40 +0200
          Re: Why does Debian allow all incoming traffic by default Gene Heskett <gheskett@shentel.net> - 2018-09-22 11:20 +0200
            Re: Why does Debian allow all incoming traffic by default Pascal Hambourg <pascal@plouf.fr.eu.org> - 2018-09-22 13:00 +0200
              Re: Why does Debian allow all incoming traffic by default Dan Ritter <dsr@randomstring.org> - 2018-09-22 13:40 +0200
                Re: Why does Debian allow all incoming traffic by default Pascal Hambourg <pascal@plouf.fr.eu.org> - 2018-09-22 17:00 +0200
                Re: Why does Debian allow all incoming traffic by default Gene Heskett <gheskett@shentel.net> - 2018-09-22 20:20 +0200
                Re: Why does Debian allow all incoming traffic by default Richard Hector <richard@walnut.gen.nz> - 2018-09-24 05:20 +0200
                Re: Why does Debian allow all incoming traffic by default Gene Heskett <gheskett@shentel.net> - 2018-09-24 05:30 +0200
                Re: Why does Debian allow all incoming traffic by default <tomas@tuxteam.de> - 2018-09-24 09:10 +0200
                Re: Why does Debian allow all incoming traffic by default Gene Heskett <gheskett@shentel.net> - 2018-09-24 11:00 +0200
                Re: Why does Debian allow all incoming traffic by default <tomas@tuxteam.de> - 2018-09-24 11:40 +0200
                Re: Why does Debian allow all incoming traffic by default Gene Heskett <gheskett@shentel.net> - 2018-09-24 14:20 +0200
                Re: Why does Debian allow all incoming traffic by default Dan Ritter <dsr@randomstring.org> - 2018-09-22 20:30 +0200
                Re: Why does Debian allow all incoming traffic by default Gene Heskett <gheskett@shentel.net> - 2018-09-22 22:20 +0200
                Re: Why does Debian allow all incoming traffic by default <tomas@tuxteam.de> - 2018-09-22 22:40 +0200
                Re: Why does Debian allow all incoming traffic by default Gene Heskett <gheskett@shentel.net> - 2018-09-22 23:20 +0200
                Re: Why does Debian allow all incoming traffic by default Simon Kengelbacher <simon.kengelbacher@mail.ch> - 2018-09-22 23:50 +0200
                Re: Why does Debian allow all incoming traffic by default Pascal Hambourg <pascal@plouf.fr.eu.org> - 2018-09-23 00:00 +0200
                Re: Why does Debian allow all incoming traffic by default Simon Kengelbacher <simon.kengelbacher@mail.ch> - 2018-09-23 00:20 +0200
                SSH X forwarding going awry (Was: Why does Debian allow all incoming  traffic by default) Étienne Mollier <etienne.mollier@mailoo.org> - 2018-09-23 11:40 +0200
                Re: SSH X forwarding going awry FIXED (Was: Why does Debian allow all incoming traffic by default) Gene Heskett <gheskett@shentel.net> - 2018-09-23 16:10 +0200
                Re: SSH X forwarding going awry FIXED (Was: Why does Debian allow  all incoming traffic by default) Joe <joe@jretrading.com> - 2018-09-23 23:00 +0200
                Re: SSH X forwarding going awry FIXED (Was: Why does Debian allow all incoming traffic by default) Gene Heskett <gheskett@shentel.net> - 2018-09-24 04:50 +0200
                Re: Why does Debian allow all incoming traffic by default Jonathan Dowland <jmtd@debian.org> - 2018-09-24 21:00 +0200
                Re: Why does Debian allow all incoming traffic by default Pascal Hambourg <pascal@plouf.fr.eu.org> - 2018-09-23 00:00 +0200
            Re: Why does Debian allow all incoming traffic by default Jonathan Dowland <jmtd@debian.org> - 2018-09-24 21:00 +0200
              Re: Why does Debian allow all incoming traffic by default Joe <joe@jretrading.com> - 2018-09-24 21:30 +0200
                Re: Why does Debian allow all incoming traffic by default Jonathan Dowland <jmtd@debian.org> - 2018-09-26 15:50 +0200
                Re: Why does Debian allow all incoming traffic by default Joe <joe@jretrading.com> - 2018-09-26 17:10 +0200
                Re: Why does Debian allow all incoming traffic by default Jonathan Dowland <jmtd@debian.org> - 2018-09-26 19:30 +0200
          Re: Why does Debian allow all incoming traffic by default Dan Purgert <dan@djph.net> - 2018-09-22 15:50 +0200
            Re: Why does Debian allow all incoming traffic by default Pascal Hambourg <pascal@plouf.fr.eu.org> - 2018-09-22 16:50 +0200
        Re: Why does Debian allow all incoming traffic by default Jonathan Dowland <jmtd@debian.org> - 2018-09-24 20:50 +0200
  Re: Why does Debian allow all incoming traffic by default Henning Follmann <hfollmann@itcfollmann.com> - 2018-09-21 15:00 +0200
    Re: Why does Debian allow all incoming traffic by default Reco <recoverym4n@gmail.com> - 2018-09-21 18:30 +0200
      Re: Why does Debian allow all incoming traffic by default Brian <ad44@cityscape.co.uk> - 2018-09-21 20:20 +0200
        Re: Why does Debian allow all incoming traffic by default Reco <recoverym4n@gmail.com> - 2018-09-21 20:40 +0200
          Re: Why does Debian allow all incoming traffic by default Brian <ad44@cityscape.co.uk> - 2018-09-21 21:10 +0200
          Re: Why does Debian allow all incoming traffic by default deloptes <deloptes@gmail.com> - 2018-09-21 23:20 +0200
            Re: Why does Debian allow all incoming traffic by default Reco <recoverym4n@gmail.com> - 2018-09-21 23:40 +0200
              Re: Why does Debian allow all incoming traffic by default Dan Purgert <dan@djph.net> - 2018-09-22 00:10 +0200
                Re: Why does Debian allow all incoming traffic by default Reco <recoverym4n@gmail.com> - 2018-09-22 09:10 +0200
                Re: Why does Debian allow all incoming traffic by default Dan Purgert <dan@djph.net> - 2018-09-22 15:50 +0200
          Re: Why does Debian allow all incoming traffic by default Pascal Hambourg <pascal@plouf.fr.eu.org> - 2018-09-22 09:50 +0200
            Re: Why does Debian allow all incoming traffic by default Reco <recoverym4n@gmail.com> - 2018-09-22 12:00 +0200
              Re: Why does Debian allow all incoming traffic by default Pascal Hambourg <pascal@plouf.fr.eu.org> - 2018-09-22 13:00 +0200
                Re: Why does Debian allow all incoming traffic by default Reco <recoverym4n@gmail.com> - 2018-09-22 13:30 +0200
                Re: Why does Debian allow all incoming traffic by default <tomas@tuxteam.de> - 2018-09-22 22:00 +0200
                Re: Why does Debian allow all incoming traffic by default Stefan Monnier <monnier@iro.umontreal.ca> - 2018-09-22 22:20 +0200
                Re: Why does Debian allow all incoming traffic by default Pascal Hambourg <pascal@plouf.fr.eu.org> - 2018-09-22 23:40 +0200
          Re: Why does Debian allow all incoming traffic by default Henning Follmann <hfollmann@itcfollmann.com> - 2018-09-22 12:10 +0200
            Re: Why does Debian allow all incoming traffic by default Reco <recoverym4n@gmail.com> - 2018-09-22 12:40 +0200
            Re: Why does Debian allow all incoming traffic by default Pascal Hambourg <pascal@plouf.fr.eu.org> - 2018-09-22 13:10 +0200
    netstat (was: Re: Why does Debian allow all incoming traffic by default) rhkramer@gmail.com - 2018-09-21 20:00 +0200
      Re: netstat Reco <recoverym4n@gmail.com> - 2018-09-21 20:20 +0200
        Re: netstat rhkramer@gmail.com - 2018-09-22 20:50 +0200
    Re: Why does Debian allow all incoming traffic by default Jonathan Dowland <jmtd@debian.org> - 2018-09-24 20:50 +0200
      Re: Why does Debian allow all incoming traffic by default Henning Follmann <hfollmann@itcfollmann.com> - 2018-09-24 21:30 +0200
        Re: Why does Debian allow all incoming traffic by default Jonathan Dowland <jmtd@debian.org> - 2018-09-26 15:50 +0200
  Re: Why does Debian allow all incoming traffic by default Pablo Álvarez Córdoba <pabloalvarezcordoba@protonmail.ch> - 2018-09-21 18:30 +0200
    Re: Why does Debian allow all incoming traffic by default Subhadip Ghosh <subhadip.sky@gmail.com> - 2018-09-21 19:30 +0200
  Re: Why does Debian allow all incoming traffic by default songbird <songbird@anthive.com> - 2018-09-22 00:10 +0200
    Re: Why does Debian allow all incoming traffic by default Joe <joe@jretrading.com> - 2018-09-22 09:40 +0200
      Re: Why does Debian allow all incoming traffic by default Pascal Hambourg <pascal@plouf.fr.eu.org> - 2018-09-22 10:40 +0200
        Re: Why does Debian allow all incoming traffic by default Joe <joe@jretrading.com> - 2018-09-22 13:20 +0200
          Re: Why does Debian allow all incoming traffic by default Pascal Hambourg <pascal@plouf.fr.eu.org> - 2018-09-22 17:10 +0200
            Re: Why does Debian allow all incoming traffic by default Joe <joe@jretrading.com> - 2018-09-23 10:50 +0200
              Re: Why does Debian allow all incoming traffic by default Pascal Hambourg <pascal@plouf.fr.eu.org> - 2018-09-27 14:00 +0200
    Re: Why does Debian allow all incoming traffic by default Jonathan Dowland <jmtd@debian.org> - 2018-09-24 20:50 +0200

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