Re: freebsd-pf Stealth Modus

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Parent Message unknown Re: freebsd-pf Stealth Modus

by Nico De Dobbeleer :: Rate this Message:

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Hello,

I just finished installing FreeBSD 7.x with pf in transparant bridging mode as the servers behind the firewall need to have an public ipaddress.
Now is everything working fine and the FW is doing his job as it should be. When I nmap the FW I see the open ports and closed ports.
Is there a way the get the FW running in stealth mode so that isn't possible anymore with nmap or any other scanning tool to see the open or closed ports?

When I look around I hear roomers that there's something like blackhole that can be added in the sysctl.

Anyone an idea?

Kind regards,
Nico
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Re: freebsd-pf Stealth Modus

by Helmut Schneider :: Rate this Message:

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From: "Nico De Dobbeleer" <nico@...>
> I just finished installing FreeBSD 7.x with pf in transparant bridging
> mode as the servers behind the firewall need to have an public
> ipaddress.  Now is everything working fine and the FW is doing his job as
> it should be. When I nmap the FW I see the open ports and closed ports.
> Is there a way the get the FW running in stealth mode so that isn't
> possible anymore with nmap or any other scanning tool to see the open or
> closed ports?

There is no "stealth". If a service responds to a request the port is
"open". If not it's closed.

Helmut

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Re: freebsd-pf Stealth Modus

by 文鳥 :: Rate this Message:

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On Tue, 6 Oct 2009 17:23:09 +0200
"Helmut Schneider" <jumper99@...> wrote:

> From: "Nico De Dobbeleer" <nico@...>
> > I just finished installing FreeBSD 7.x with pf in transparant
> > bridging mode as the servers behind the firewall need to have an
> > public ipaddress.  Now is everything working fine and the FW is
> > doing his job as it should be. When I nmap the FW I see the open
> > ports and closed ports. Is there a way the get the FW running in
> > stealth mode so that isn't possible anymore with nmap or any other
> > scanning tool to see the open or closed ports?
>
> There is no "stealth". If a service responds to a request the port is
> "open". If not it's closed.
>
> Helmut

There is: just use "block drop" in your pf config or "set block-policy
drop" (see man 5 pf.conf). This effectively stops sending TCP RST or
UDP unreach packets.
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Re: freebsd-pf Stealth Modus

by Helmut Schneider :: Rate this Message:

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文鳥 <bunchou@...> wrote:

> On Tue, 6 Oct 2009 17:23:09 +0200
> "Helmut Schneider" <jumper99@...> wrote:
>
>> From: "Nico De Dobbeleer" <nico@...>
>>> I just finished installing FreeBSD 7.x with pf in transparant
>>> bridging mode as the servers behind the firewall need to have an
>>> public ipaddress.  Now is everything working fine and the FW is
>>> doing his job as it should be. When I nmap the FW I see the open
>>> ports and closed ports. Is there a way the get the FW running in
>>> stealth mode so that isn't possible anymore with nmap or any other
>>> scanning tool to see the open or closed ports?
>>
>> There is no "stealth". If a service responds to a request the port is
>> "open". If not it's closed.
>
> There is: just use "block drop" in your pf config or "set block-policy
> drop" (see man 5 pf.conf). This effectively stops sending TCP RST or
> UDP unreach packets.

Consider a webserver where you pass HTTP and "block drop" SSH. 1 port is
open -> host not "stealth".

But even if you "block drop" all incoming traffic to a host, if a host is
really down (and therefore stealth) the hosts' gateway would send an ICMP
type 3 packet (until you didn't cripple ICMP as well).

While sometimes it might be useful to "block drop" it has nothing to do with
being "stealth".

Helmut


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Re: freebsd-pf Stealth Modus

by 文鳥 :: Rate this Message:

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On Tue, 6 Oct 2009 20:28:33 +0200
"Helmut Schneider" <jumper99@...> wrote:

> 文鳥 <bunchou@...> wrote:
> > On Tue, 6 Oct 2009 17:23:09 +0200
> > "Helmut Schneider" <jumper99@...> wrote:
> >
> >> From: "Nico De Dobbeleer" <nico@...>
> >>> I just finished installing FreeBSD 7.x with pf in transparant
> >>> bridging mode as the servers behind the firewall need to have an
> >>> public ipaddress.  Now is everything working fine and the FW is
> >>> doing his job as it should be. When I nmap the FW I see the open
> >>> ports and closed ports. Is there a way the get the FW running in
> >>> stealth mode so that isn't possible anymore with nmap or any other
> >>> scanning tool to see the open or closed ports?
> >>
> >> There is no "stealth". If a service responds to a request the port
> >> is "open". If not it's closed.
> >
> > There is: just use "block drop" in your pf config or "set
> > block-policy drop" (see man 5 pf.conf). This effectively stops
> > sending TCP RST or UDP unreach packets.
>
> Consider a webserver where you pass HTTP and "block drop" SSH. 1 port
> is open -> host not "stealth".
>
> But even if you "block drop" all incoming traffic to a host, if a
> host is really down (and therefore stealth) the hosts' gateway would
> send an ICMP type 3 packet (until you didn't cripple ICMP as well).
>
> While sometimes it might be useful to "block drop" it has nothing to
> do with being "stealth".
>
> Helmut

Not replying to a probe in the mentioned way is exactly what is
commonly referred to as "stealth mode" by consumer firewalls. Just try
a simple google search for "stealth firewall" and you will see.
Besides, if only a few (uncommon) ports are open, a limited scan is
unlikely to find them, thus calling it "stealth" (aka "low
observability" according to wikipedia) is appropriate imho. There is a
difference between stealth and invisibility.
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Re: freebsd-pf Stealth Modus

by Helmut Schneider :: Rate this Message:

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文鳥 <bunchou@...> wrote:

> On Tue, 6 Oct 2009 20:28:33 +0200
> "Helmut Schneider" <jumper99@...> wrote:
>
>> 文鳥 <bunchou@...> wrote:
>>> On Tue, 6 Oct 2009 17:23:09 +0200
>>> "Helmut Schneider" <jumper99@...> wrote:
>>>
>>>> From: "Nico De Dobbeleer" <nico@...>
>>>>> I just finished installing FreeBSD 7.x with pf in transparant
>>>>> bridging mode as the servers behind the firewall need to have an
>>>>> public ipaddress.  Now is everything working fine and the FW is
>>>>> doing his job as it should be. When I nmap the FW I see the open
>>>>> ports and closed ports. Is there a way the get the FW running in
>>>>> stealth mode so that isn't possible anymore with nmap or any other
>>>>> scanning tool to see the open or closed ports?
>>>>
>>>> There is no "stealth". If a service responds to a request the port
>>>> is "open". If not it's closed.
>>>
>>> There is: just use "block drop" in your pf config or "set
>>> block-policy drop" (see man 5 pf.conf). This effectively stops
>>> sending TCP RST or UDP unreach packets.
>>
>> Consider a webserver where you pass HTTP and "block drop" SSH. 1 port
>> is open -> host not "stealth".
>>
>> But even if you "block drop" all incoming traffic to a host, if a
>> host is really down (and therefore stealth) the hosts' gateway would
>> send an ICMP type 3 packet (until you didn't cripple ICMP as well).
>>
>> While sometimes it might be useful to "block drop" it has nothing to
>> do with being "stealth".
>
> Not replying to a probe in the mentioned way is exactly what is
> commonly referred to as "stealth mode" by consumer firewalls. Just try
> a simple google search for "stealth firewall" and you will see.

I know the term "stealth firewall" very well. It's a worthless marketing
buzzword. It suggests users that it could prevent an attack or even the scan
itself. Neither is correct. This is what I wanted to point out and I was
encouraged by the fact that the OP was talking about "stealthing" open
ports.


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Re: freebsd-pf Stealth Modus

by 文鳥 :: Rate this Message:

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On Wed, 7 Oct 2009 11:40:36 +0200
"Helmut Schneider" <jumper99@...> wrote:

> 文鳥 <bunchou@...> wrote:
> > On Tue, 6 Oct 2009 20:28:33 +0200
> > "Helmut Schneider" <jumper99@...> wrote:
> >
> >> 文鳥 <bunchou@...> wrote:
> >>> On Tue, 6 Oct 2009 17:23:09 +0200
> >>> "Helmut Schneider" <jumper99@...> wrote:
> >>>
> >>>> From: "Nico De Dobbeleer" <nico@...>
> >>>>> I just finished installing FreeBSD 7.x with pf in transparant
> >>>>> bridging mode as the servers behind the firewall need to have an
> >>>>> public ipaddress.  Now is everything working fine and the FW is
> >>>>> doing his job as it should be. When I nmap the FW I see the open
> >>>>> ports and closed ports. Is there a way the get the FW running in
> >>>>> stealth mode so that isn't possible anymore with nmap or any
> >>>>> other scanning tool to see the open or closed ports?
> >>>>
> >>>> There is no "stealth". If a service responds to a request the
> >>>> port is "open". If not it's closed.
> >>>
> >>> There is: just use "block drop" in your pf config or "set
> >>> block-policy drop" (see man 5 pf.conf). This effectively stops
> >>> sending TCP RST or UDP unreach packets.
> >>
> >> Consider a webserver where you pass HTTP and "block drop" SSH. 1
> >> port is open -> host not "stealth".
> >>
> >> But even if you "block drop" all incoming traffic to a host, if a
> >> host is really down (and therefore stealth) the hosts' gateway
> >> would send an ICMP type 3 packet (until you didn't cripple ICMP as
> >> well).
> >>
> >> While sometimes it might be useful to "block drop" it has nothing
> >> to do with being "stealth".
> >
> > Not replying to a probe in the mentioned way is exactly what is
> > commonly referred to as "stealth mode" by consumer firewalls. Just
> > try a simple google search for "stealth firewall" and you will see.
>
> I know the term "stealth firewall" very well. It's a worthless
> marketing buzzword. It suggests users that it could prevent an attack
> or even the scan itself. Neither is correct. This is what I wanted to
> point out and I was encouraged by the fact that the OP was talking
> about "stealthing" open ports.

Ok, I totally agree with your reasoning when it comes to the open
ports and useless marketing hype. Nevertheless, I think that the word
"stealth" fits very well in the case of closed ports as it makes it
a (slight) bit harder to find if a host is up or not.

Anyway, even if the OP's mail was a bit misleading, I think
it would have helped him more if you had just explained what
'stealth' actually means, why you and steered him into the right
direction in addition to what you wrote. And it would also have
prevented this prolonged and utterly useless discussion we were
leading ;)
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Re: freebsd-pf Stealth Modus

by Helmut Schneider :: Rate this Message:

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文鳥 <bunchou@...> wrote:

> On Wed, 7 Oct 2009 11:40:36 +0200
> "Helmut Schneider" <jumper99@...> wrote:
>> I know the term "stealth firewall" very well. It's a worthless
>> marketing buzzword. It suggests users that it could prevent an attack
>> or even the scan itself. Neither is correct. This is what I wanted to
>> point out and I was encouraged by the fact that the OP was talking
>> about "stealthing" open ports.
>
> Ok, I totally agree with your reasoning when it comes to the open
> ports and useless marketing hype. Nevertheless, I think that the word
> "stealth" fits very well in the case of closed ports as it makes it
> a (slight) bit harder to find if a host is up or not.

Well, I still disagree.

> Anyway, even if the OP's mail was a bit misleading, I think
> it would have helped him more if you had just explained what
> 'stealth' actually means, why you and steered him into the right
> direction in addition to what you wrote. And it would also have
> prevented this prolonged and utterly useless discussion we were
> leading ;)

Again I disagree, I expect this discussion to be useful for many others.

But I agree, we should stop at that point. :)

Helmut


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