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Show HN: Automatic proxy setup for SSH'able boxes that have no network access

51 points by _jhqp 5y ago

1cvmask 5y ago
I couldn't find the license for it. Is it open source? If so what license?
- _jhqp 5y ago
  I added MIT license now :)
_jhqp 5y ago
All comments & suggestions / code reviews are welcome!
SahAssar 5y ago
I don't really get what the definition of "network" is here, clearly the box has network access since it is SSH'able. Could you give an example of a situation when this is used?
- _jhqp 5y ago
  "Network access" as in outgoing requests to public web. e.g. you can't curl google.com I've used this code in CTF competitions and Blue Team exercises where some machines behind a VPN don't have outgoing network access. (Sometimes it's just simpler to organize this way, sometimes it's deliberate for security purposes.)
  - SahAssar 5y ago
    So restricted HTTP access, but wide open SSH? Do people commonly restrict only HTTP/HTTPS but leave other ports unrestricted?
    - jve 5y ago
      Yeah, well, not only HTTP*, but actually whitelisting whatever outgoing connection you may need. https://github.com/stripe/smokescreen https://github.com/stripe/smokescreen Suppose you configured your webserver to run with limited privileges so as if someone hacks it it has limited access. Suppose it still has access to DB and stuff. Well, filtering outgoing connections makes harder to exfiltrate the data OR hop to another hosts. And then you can monitor failed outgoing requests to be able to act/investigate when that happens.
      - SahAssar 5y ago
        Couldn't an attacker exfiltrate over ssh or over an incoming HTTP connection instead of an outgoing? Or is this a defense-in-depth thing, not meant as a "hard stop"?
        jve 5y ago
        I see this as a defense in depth. It can buy you time until attacker figures out how to exfiltrate and you maybe notice via monitoring that something fishy is happening. It also prevents you participating in a DoS or other attacks.
      - stevekemp 5y ago
        Yeah there are a bunch of tools like this - I'm using Aviatrix at the moment for a bunch of hosts: * Incoming access is allowed to "stuff" when connected to the OpenVPN host. * Outgoing access to services is very heavily restricted. * Outgoing HTTP/HTTPS requires the site to be on an allow-list. By default all outgoing HTTP/HTTPS traffic is denied. (We might add yum-repositories to the allowlist, or permit access to the various "Windows Updates" services, for example. But all other downloads from remote sites would be denied.)
    - thedougd 5y ago
      This would be a common setup. They allow SSH ingress so that the server can be managed or provisioned with something like Ansible. However, they block all other unused ingress ports, as well as any egress that does not contribute to the function of the server. Also common would be a bastion or VPN to get to the network where SSH is accessible. A mistake is to have SSH accessible to the entire corporate network, which is all too common.
- gizdan 5y ago
  Not OP, but some air-gapped servers can be connected to from a private "trusted" network, but are otherwise unable to connect to the internet or elsewhere. Perhaps that's what OP means? I wish companies would hurry up and move away from "trusted" networks and move onto zero trust.
  - _jhqp 5y ago
    Exactly. These "trusted" machines still have security vulnerabilities that you would like to patch though :)
  - traceroute66 5y ago
    > some air-gapped servers can be connected to from a private "trusted" network Erm ... mate.... A device is either air-gapped or it isn't. The clue is kinda in the name. Yes, I know gov/mil networks use data-diodes, but that's a different kettle of very expensive fish which is certified to EAL6/7. For everyone else, air-gapped means what it says on the tin. Pseudo air-gapping via firewall rules is not air-gapping, its called writing ACLs.
    - 123pie123 5y ago
      correct - I think people are getting confused - not sure how, since the name is very descriptive
    - myself248 5y ago
      Bingo. Air-gapped machines, by definition, have no connection to each other. Not so much as an audio cable between them. Everything that goes back and forth is manually transferred, either by eyes-on-one-screen-hands-on-the-other-keyboard, or by sneakernet typically of media which may be inspected at yet a third station en route. This is a proxy or a bastion host, no more, no less. Calling it an airgap, even in "scare quotes", is clownishly terrible and serves no purpose beyond polluting the language.
    - gizdan 5y ago
      Ha. I totally get what you mean, but I wish. I've seen plenty of air-gapped servers, and I'm not even that old. And everytime I've challenged the set up for it to be truly air-gapped, I've been fought for it.
- mrweasel 5y ago
  The name, Airgapt - "airgapped" apt, is also a little "weird". When I work on air gapped devices it normally involved bringing DVDs and physically going to a datacenter.
  - _jhqp 5y ago
    Agreed :) That's why I put it in "quotes" Can you propose an alternative / more accurate name?
    - mrweasel 5y ago
      I'd rather not :-) Naming things is hard. I love the project though, not because I need it, but it proves one of my point: "If you didn't want me to be able to do X, then you shouldn't have allowed SSH access".
    - deleted 5y ago
      [deleted]
  - 3np 5y ago
    I think the name is quite apt (:
- Fnoord 5y ago
  You could have a bridge (e.g. with an IDS or a packet filter) with a management interface on a separate VLAN, or which requires management via a physical cable of some sort. But the bridge could also intercept traffic to port 22 and redirect it to itself. Personally, I resort to Wireguard instead being the only reachable port.
gjulianm 5y ago
Something to add: use proxychains to ensure that the requests of all apps go through the proxy. A lot of applications don't have good proxy support, or have nothing at all. If you configure proxychains with the SOCKS proxy provided by this script, then you can do "proxychains my-command-that-doesnt-use-proxy" and it will automatically patch the libc calls to use the proxy properly.
- _jhqp 5y ago
  Good suggestion. Added it to the README as an optional addition.
rp1 5y ago
Isn’t this typically called an ssh bastion?
- _jhqp 5y ago
  Looks like :) https://github.com/ovh/the-bastion https://github.com/ovh/the-bastion
  - _jhqp 5y ago
    Though after looking into it more, it seems to me like bastions usually aren't used for reverse proxy / SOCKS like this. Usually bastions are just allowing one SSH server on your VPC/network and every SSH connection going through it. I still actually haven't found similar projects to mine.
    - egberts1 5y ago
      Bastion SSH? This new-finagle “airgapt” makes GatewayPorts sshd_option setting of OpenSSL kinda useless? My code review notes says: # GatewayPorts specifies whether remote hosts are # allowed to connect to ports forwarded for the # client. By default, sshd(8) binds remote port # forwardings to the loopback address. This prevents # other remote hosts from connecting to forwarded # ports. GatewayPorts can be used to specify that sshd # should allow remote port forwardings to bind to # non-loopback addresses, thus allowing other hosts to # connect. The argument may be no to force remote port # forwardings to be available to the local host only, # yes to force remote port forwardings to bind to the # wildcard address, or clientspecified to allow the # client to select the address to which the forwarding # is bound. # # CLI option: -o # options.fwd_opts.gateway_ports/channel_fwd_bind_addr()/channel_setup_fwd_listener_tcpip()/channel_setup_remote_fwd_listener() # options.fwd_opts.gateway_ports/channel_fwd_bind_addr()/channel_setup_fwd_listener_tcpip()/channel_setup_local_fwd_listener() # GatewayPorts defaults to 'no'.
      - _jhqp 5y ago
        You are absolutely correct. I updated to not use GatewayPorts in v0.1.1 Thank you for the feedback! https://github.com/AkselAllas/airgapt/issues/1 https://github.com/AkselAllas/airgapt/issues/1
egberts1 5y ago
Only way to block this is that “airgapt” thingie is hopefully this sshd_config setting: # DisableForwarding disables all forwarding features, # including X11, ssh-agent(1), TCP and StreamLocal. # This option overrides all other forwarding-related # options and may simplify restricted configurations. # # CLI option: -o # options.disable_forwarding/do_authenticated() DisableForwarding no
egberts1 5y ago
I love the innocuous application of enabling just the Debian package management behind such draconian firewalls. Makes me wonder if there are any other applications to be had there. (I am a JavaScript pentester)

51 points by _jhqp 5y ago

1cvmask 5y ago

I couldn't find the license for it. Is it open source? If so what license?

_jhqp 5y ago
I added MIT license now :)

_jhqp 5y ago

All comments & suggestions / code reviews are welcome!

SahAssar 5y ago

I don't really get what the definition of "network" is here, clearly the box has network access since it is SSH'able. Could you give an example of a situation when this is used?

_jhqp 5y ago
"Network access" as in outgoing requests to public web. e.g. you can't curl google.com I've used this code in CTF competitions and Blue Team exercises where some machines behind a VPN don't have outgoing network access. (Sometimes it's just simpler to organize this way, sometimes it's deliberate for security purposes.)
- SahAssar 5y ago
  So restricted HTTP access, but wide open SSH? Do people commonly restrict only HTTP/HTTPS but leave other ports unrestricted?
  - jve 5y ago
    Yeah, well, not only HTTP*, but actually whitelisting whatever outgoing connection you may need. https://github.com/stripe/smokescreen https://github.com/stripe/smokescreen Suppose you configured your webserver to run with limited privileges so as if someone hacks it it has limited access. Suppose it still has access to DB and stuff. Well, filtering outgoing connections makes harder to exfiltrate the data OR hop to another hosts. And then you can monitor failed outgoing requests to be able to act/investigate when that happens.
    - SahAssar 5y ago
      Couldn't an attacker exfiltrate over ssh or over an incoming HTTP connection instead of an outgoing? Or is this a defense-in-depth thing, not meant as a "hard stop"?
      - jve 5y ago
        I see this as a defense in depth. It can buy you time until attacker figures out how to exfiltrate and you maybe notice via monitoring that something fishy is happening. It also prevents you participating in a DoS or other attacks.
    - stevekemp 5y ago
      Yeah there are a bunch of tools like this - I'm using Aviatrix at the moment for a bunch of hosts: * Incoming access is allowed to "stuff" when connected to the OpenVPN host. * Outgoing access to services is very heavily restricted. * Outgoing HTTP/HTTPS requires the site to be on an allow-list. By default all outgoing HTTP/HTTPS traffic is denied. (We might add yum-repositories to the allowlist, or permit access to the various "Windows Updates" services, for example. But all other downloads from remote sites would be denied.)
  - thedougd 5y ago
    This would be a common setup. They allow SSH ingress so that the server can be managed or provisioned with something like Ansible. However, they block all other unused ingress ports, as well as any egress that does not contribute to the function of the server. Also common would be a bastion or VPN to get to the network where SSH is accessible. A mistake is to have SSH accessible to the entire corporate network, which is all too common.
gizdan 5y ago
Not OP, but some air-gapped servers can be connected to from a private "trusted" network, but are otherwise unable to connect to the internet or elsewhere. Perhaps that's what OP means? I wish companies would hurry up and move away from "trusted" networks and move onto zero trust.
- _jhqp 5y ago
  Exactly. These "trusted" machines still have security vulnerabilities that you would like to patch though :)
- traceroute66 5y ago
  > some air-gapped servers can be connected to from a private "trusted" network Erm ... mate.... A device is either air-gapped or it isn't. The clue is kinda in the name. Yes, I know gov/mil networks use data-diodes, but that's a different kettle of very expensive fish which is certified to EAL6/7. For everyone else, air-gapped means what it says on the tin. Pseudo air-gapping via firewall rules is not air-gapping, its called writing ACLs.
  - 123pie123 5y ago
    correct - I think people are getting confused - not sure how, since the name is very descriptive
  - myself248 5y ago
    Bingo. Air-gapped machines, by definition, have no connection to each other. Not so much as an audio cable between them. Everything that goes back and forth is manually transferred, either by eyes-on-one-screen-hands-on-the-other-keyboard, or by sneakernet typically of media which may be inspected at yet a third station en route. This is a proxy or a bastion host, no more, no less. Calling it an airgap, even in "scare quotes", is clownishly terrible and serves no purpose beyond polluting the language.
  - gizdan 5y ago
    Ha. I totally get what you mean, but I wish. I've seen plenty of air-gapped servers, and I'm not even that old. And everytime I've challenged the set up for it to be truly air-gapped, I've been fought for it.
mrweasel 5y ago
The name, Airgapt - "airgapped" apt, is also a little "weird". When I work on air gapped devices it normally involved bringing DVDs and physically going to a datacenter.
- _jhqp 5y ago
  Agreed :) That's why I put it in "quotes" Can you propose an alternative / more accurate name?
  - mrweasel 5y ago
    I'd rather not :-) Naming things is hard. I love the project though, not because I need it, but it proves one of my point: "If you didn't want me to be able to do X, then you shouldn't have allowed SSH access".
  - deleted 5y ago
    [deleted]
- 3np 5y ago
  I think the name is quite apt (:
Fnoord 5y ago
You could have a bridge (e.g. with an IDS or a packet filter) with a management interface on a separate VLAN, or which requires management via a physical cable of some sort. But the bridge could also intercept traffic to port 22 and redirect it to itself. Personally, I resort to Wireguard instead being the only reachable port.

gjulianm 5y ago

Something to add: use proxychains to ensure that the requests of all apps go through the proxy. A lot of applications don't have good proxy support, or have nothing at all. If you configure proxychains with the SOCKS proxy provided by this script, then you can do "proxychains my-command-that-doesnt-use-proxy" and it will automatically patch the libc calls to use the proxy properly.

_jhqp 5y ago
Good suggestion. Added it to the README as an optional addition.

rp1 5y ago

Isn’t this typically called an ssh bastion?

_jhqp 5y ago
Looks like :) https://github.com/ovh/the-bastion https://github.com/ovh/the-bastion
- _jhqp 5y ago
  Though after looking into it more, it seems to me like bastions usually aren't used for reverse proxy / SOCKS like this. Usually bastions are just allowing one SSH server on your VPC/network and every SSH connection going through it. I still actually haven't found similar projects to mine.
  - egberts1 5y ago
    Bastion SSH? This new-finagle “airgapt” makes GatewayPorts sshd_option setting of OpenSSL kinda useless? My code review notes says: # GatewayPorts specifies whether remote hosts are # allowed to connect to ports forwarded for the # client. By default, sshd(8) binds remote port # forwardings to the loopback address. This prevents # other remote hosts from connecting to forwarded # ports. GatewayPorts can be used to specify that sshd # should allow remote port forwardings to bind to # non-loopback addresses, thus allowing other hosts to # connect. The argument may be no to force remote port # forwardings to be available to the local host only, # yes to force remote port forwardings to bind to the # wildcard address, or clientspecified to allow the # client to select the address to which the forwarding # is bound. # # CLI option: -o # options.fwd_opts.gateway_ports/channel_fwd_bind_addr()/channel_setup_fwd_listener_tcpip()/channel_setup_remote_fwd_listener() # options.fwd_opts.gateway_ports/channel_fwd_bind_addr()/channel_setup_fwd_listener_tcpip()/channel_setup_local_fwd_listener() # GatewayPorts defaults to 'no'.
    - _jhqp 5y ago
      You are absolutely correct. I updated to not use GatewayPorts in v0.1.1 Thank you for the feedback! https://github.com/AkselAllas/airgapt/issues/1 https://github.com/AkselAllas/airgapt/issues/1

egberts1 5y ago

Only way to block this is that “airgapt” thingie is hopefully this sshd_config setting: # DisableForwarding disables all forwarding features, # including X11, ssh-agent(1), TCP and StreamLocal. # This option overrides all other forwarding-related # options and may simplify restricted configurations. # # CLI option: -o # options.disable_forwarding/do_authenticated() DisableForwarding no

egberts1 5y ago

I love the innocuous application of enabling just the Debian package management behind such draconian firewalls. Makes me wonder if there are any other applications to be had there. (I am a JavaScript pentester)