Comment on PSA: Docker nukes your firewall rules, and replaces them with its own.

JustEnoughDucks@feddit.nl ⁨8⁩ ⁨months⁩ ago

• justJanne@startrek.website ⁨8⁩ ⁨months⁩ ago

  That assumes you’re on some VPS with a hardware firewall in front.

  Often enough you’re on a dedicated server that’s directly exposed to the internet, with those iptables rules being the only thing standing between your services and the internet.

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  • lemmyvore@feddit.nl ⁨8⁩ ⁨months⁩ ago

    What difference does it make if you open the ports yourself for the services you expose, or Docker does it for you? That’s all that Docker is meant to do, act as convenience so you don’t have to add/remove rules as the containers go up/down, or remember Docker interfaces.

    If by any chance you are making services listen on 0.0.0.0 and covering them up with a firewall that’s very bad practice.

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    • justJanne@startrek.website ⁨8⁩ ⁨months⁩ ago

      There’s no alternative for 0.0.0.0 and a firewall if you’re e.g. using kubernetes.

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      • lemmyvore@feddit.nl ⁨8⁩ ⁨months⁩ ago

        I’m fairly sure you can find an alternative to whatever problem you’re having.

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• moonpiedumplings@programming.dev ⁨8⁩ ⁨months⁩ ago

  Yes it is a security risk, but if you don’t have all ports forwarded, someone would still have to breach your internal network IIRC, so you would have many many more problems than docker.

  I think from the dev’s point of view (not that it is right or wrong), this is intended behavior simply because if docker didn’t do this, they would get 1,000 issues opened per day of people saying containers don’t work when they forgot to add a firewall rules for a new container.

  My problem with this, is that when running a public facing server, this ends up with people exposing containers that really, really shouldn’t be exposed.

  Excerpt from another comment of mine:

  It’s only docker where you have to deal with something like this:

  ---
  services:
    webtop:
      image: lscr.io/linuxserver/webtop:latest
      container_name: webtop
      security_opt:
        - seccomp:unconfined #optional
      environment:
        - PUID=1000
        - PGID=1000
        - TZ=Etc/UTC
        - SUBFOLDER=/ #optional
        - TITLE=Webtop #optional
      volumes:
        - /path/to/data:/config
        - /var/run/docker.sock:/var/run/docker.sock #optional
      ports:
        - 3000:3000
        - 3001:3001
      restart: unless-stopped
  

  Originally from here, edited for brevity.

  Resulting in exposed services. Feel free to look at shodan or zoomeye, internet connected search engines, for exposed versions of this service. This service is highly dangerous to expose, as it gives people an in to your system via the docker socket.

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  • adam@doomscroll.n8e.dev ⁨8⁩ ⁨months⁩ ago

    But… You literally have ports rules in there. Rules that expose ports.

    You don’t get to grumble that docker is doing something when you’re telling it to do it

    Dockers manipulation of nftables is pretty well defined in their documentation. If you dig deep everything is tagged and natted through to the docker internal networks.

    As to the usage of the docker socket that is widely advised against unless you really know what you’re doing.

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    • moonpiedumplings@programming.dev ⁨8⁩ ⁨months⁩ ago

      Dockers manipulation of nftables is pretty well defined in their documentation

      Documentation people don’t read. People expect, that, like most other services, docker binds to ports/addresses behind the firewall. Literally no other container runtime/engine does this, including, notably, podman.

      As to the usage of the docker socket that is widely advised against unless you really know what you’re doing.

      Too bad people don’t read that advice. They just deploy the webtop docker compose, without understanding what any of it is. I like (hate?) linuxserver’s webtop, because it’s an example of the two of the worst footguns in docker in one

      To include the rest of my comment that I linked to:

      Do any of those poor saps on zoomeye expect that I can pwn them by literally opening a webpage?

      No. They expect their firewall to protect them by not allowing remote traffic to those ports. You can argue semantics all you want, but not informing people of this gives them another footgun to shoot themselves with. Hence, docker “bypasses” the firewall.

      On the other hand, podman respects your firewall rules. Yes, you have to edit the rules yourself. But that’s better than a footgun. The literal point of a firewall is to ensure that any services you accidentally have running aren’t exposed to the internet, and docker throws that out the window.

      Your original point was:

      I think from the dev’s point of view (not that it is right or wrong), this is intended behavior simply because if docker didn’t do this, they would get 1,000 issues opened per day of people saying containers don’t work when they forgot to add a firewall rules for a new container.

      And I’m trying to say that even if that was true, it would still be better than a footgun where people expose stuff that’s not supposed to be exposed.

      But that isn’t the case for podman. A quick look through the github issues for podman, and I don’t see it inundated with newbies asking “how to expose services?” because they assume the firewall port needs to be opened, probably. Instead, there are bug reports in the opposite direction, like this one, where services are being exposed despite the firewall being up.

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      • adam@doomscroll.n8e.dev ⁨8⁩ ⁨months⁩ ago

        Documentation people don’t read Too bad people don’t read that advice

        Sure, I get it, this stuff should be accessible for all. Easy to use with sane defaults and all that. But at the end of the day anyone wanting to using this stuff is exposing potential/actual vulenerabilites to the internet (via the OS, the software stack, the configuration, … ad nauseum), and the management and ultimate responsibility for that falls on their shoulders.

        If they’re not doing the absolute minimum of R’ingTFM for something as complex as Docker then what else has been missed?

        People expect, that, like most other services, docker binds to ports/addresses behind the firewall

        Unless you tell it otherwise that’s exactly what it does. If you don’t bind ports good luck accessing your NAT’d 172.17.0.x:3001 service from the internet. Podman has the exact same functionality.

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  • null@slrpnk.net ⁨8⁩ ⁨months⁩ ago

    My solution to this has been to not forward the ports on individual services at all. I put a reverse proxy in front of them, refer to them by container name in the reverse proxy settings, and make sure they’re on the same docker network.

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  • wreckedcarzz@lemmy.world ⁨8⁩ ⁨months⁩ ago

    So uh, I just spun up a vps a couple days ago, few docker containers, usual security best practices… I used ufw to block all and open only ssh and a couple others, as that’s what I’ve been told that I need to do. Should I be panicking about my containers fucking with the firewall?

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    • moonpiedumplings@programming.dev ⁨8⁩ ⁨months⁩ ago

      Probably not an issue, but you should check. If the port opened is something like 127.0.0.1:portnumber, then it’s only bound to localhost, and only that local machine can access it. If no address is specified, then anyone with access to the server can access that service.

      An easy way to see containers running is: docker ps, where you can look at forwarded ports.

      Alternatively, you can use the nmap tool to scan your own server for exposed ports. nmap -A serverip does the slowest, but most indepth scan.

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      • wreckedcarzz@lemmy.world ⁨8⁩ ⁨months⁩ ago

        Just waking up, I’ve been running docker on my nas for a few years now and was never made aware of this - the nas ports appear safe, but the vps is not, so I swapped in 127.0.0.1 in front of the port number (so it’s now 127.0.0.1:8080:80 or what have you), and that appears to resolve it. I have nginx running so of course that’s how I want to have a couple things exposed, not everything via port.

        My understanding was that port:port just was local for allowing redirection from container to host, and you’d still need to do network firewall management yourself to allow stuff through, and that appears the case on my home network, so I never had reason to question it. Thanks, I learned something today :)

        Might do the same to my nas containers, too, just to be safe. I’m using those containers as a testbed for the vps containers so I don’t want to forget…

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    • adam@doomscroll.n8e.dev ⁨8⁩ ⁨months⁩ ago

      Docker will have only exposed container ports if you told it to.

      If you used -p 8080:80 (cli) or - 8080:80 (docker-compose) then docker will have dutifully NAT’d those ports through your firewall. You can either not do either of those if it’s a port you don’t want exposed or as @moonpiedumplings@programming.dev says below you can ensure it’s only mapped to localhost (or an otherwise non-public) IP.

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      • wreckedcarzz@lemmy.world ⁨8⁩ ⁨months⁩ ago

        Thanks - more detailed reply below :)

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    • droolio@feddit.uk ⁨8⁩ ⁨months⁩ ago

      Actually, ufw has its own separate issue you may need to deal with. (Or bind ports to localhost/127.0.0.1 as others have stated.)

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• N0x0n@lemmy.ml ⁨8⁩ ⁨months⁩ ago

  Option to disable this behavior would be 100x better then current, but what do I know lol

  Prevent docker from manipulating iptables

  Don’t know what it’s actually doing, I’m just learning how to work with nftables, but I saved that link in case oneday I want to manage the iptables rules myself :)

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  • Auli@lemmy.ca ⁨8⁩ ⁨months⁩ ago

    Good luck. Your going to have to change the rules whenever the up address of the container changes.

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    • N0x0n@lemmy.ml ⁨8⁩ ⁨months⁩ ago

      If you are talking about the IP address then just add a static address, no? I do it anyway in my docker compose:

      ...
          networks:
            traefik.net:
              ipv4_address: 10.10.10.99
      
      networks:
          traefik.net:
            name: traefik-net
            external: true
      

      I’m not an expert so maybe I’m wrong, if so do not hesitate to correct me !

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• Kalcifer@sh.itjust.works ⁨8⁩ ⁨months⁩ ago

  IIRC, doesn’t modify actual incoming rules (at least it doesn’t for me)

  How come I don’t see my previous rules when I dump the ruleset, then? I have my rules written in /etc/nftables.conf, and they were previously applied by running # nft -f /etc/nftables.conf. Now, when I dump the current ruleset with # nft list ruleset, those previous rules aren’t there — all I see are Docker’s rules.

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