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Rayne
Asked: 2022-04-01 02:42:03 +0800 CST

How to block all outgoing connections from a particular user except localhost?

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I wish to block all outgoing connections from a particular user user after they have ssh'd into my server (running RHEL 7.4), that is, user should not be able to ssh into/ping other servers on the network.

I initially configured the following firewall-cmd rule, and it was working.

firewall-cmd --direct --permanent --add-rule ipv4 filter OUTPUT 0 -m owner --uid-owner user -j DROP

However, user now needs to access Jupyter Notebook also running on the same server (http://localhost:8888), but was unable to. There was an error about the websocket. Once the firewall rule above was removed, user can access the Notebook.

I'm not sure why user was unable to access localhost, because I thought the rule only blocks outgoing connections.

How do I allow user to access localhost on any port, or a specific port range, while still blocking network access to everywhere else?

firewall-cmd

1 Answers

  1. As djdomi mentioned, you'd like to add an exception before that DROP rule you already have. This could work

    firewall-cmd --direct --permanent --add-rule ipv4 filter OUTPUT 0 -m owner --uid-owner user --dport=8888 -j ACCEPT

    Place it before the rule yuo already have.

    BR

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