Netgate Discussion Forum
    • Categories
    • Recent
    • Tags
    • Popular
    • Users
    • Search
    • Register
    • Login

    How to block FIN packets?

    Scheduled Pinned Locked Moved General pfSense Questions
    4 Posts 3 Posters 1.4k Views
    Loading More Posts
    • Oldest to Newest
    • Newest to Oldest
    • Most Votes
    Reply
    • Reply as topic
    Log in to reply
    This topic has been deleted. Only users with topic management privileges can see it.
    • Y
      yourcatbites
      last edited by

      Hi,

      I am facing an issue with "invalid" FIN packets that garbage my audit logs. A short search brought me here:
      https://doc.pfsense.org/index.php/Why_do_my_logs_show_%22blocked%22_for_traffic_from_a_legitimate_connection

      My solution to this, is no add a block rule before the default "Deny All", that only blocks FIN packets with no-log option on.

      Any idea to how this can be done?

      Thanks!

      1 Reply Last reply Reply Quote 0
      • johnpozJ
        johnpoz LAYER 8 Global Moderator
        last edited by

        Are the invalid FIN coming from lan side or wan/internet side?  If coming from lan - shouldn't you look to what is causing the issue vs just not logging ;)

        Even if from the internet maybe look into why??

        An intelligent man is sometimes forced to be drunk to spend time with his fools
        If you get confused: Listen to the Music Play
        Please don't Chat/PM me for help, unless mod related
        SG-4860 24.11 | Lab VMs 2.8, 24.11

        1 Reply Last reply Reply Quote 0
        • H
          Harvy66
          last edited by

          Making the huge assumption that I was creating the rule correctly and that I am remembering from over a year ago correctly.

          I've tried this before, and it seems PFSense only cares about SYN packets for TCP. Since it's stateful, the only time packets need to be checked is when a connection is attempting to be created and the only way to create a TCP connection is with a SYN packet. with my limited understanding, it seems there is no way to block out of state TCP packets with a custom rule. I think I even tried creating my own block-all rule, and it was ignored for out of state packets, but it was a long time ago and I may be creating fake memories based on what I would now think I should test.

          1 Reply Last reply Reply Quote 0
          • johnpozJ
            johnpoz LAYER 8 Global Moderator
            last edited by

            I think OP is correct, creating a rule with the flag settings, if you set a rule and set FIN being set and blocked it without logging that should work

            If the packet matched a state then it wouldn't be logged.  If out of state it would be logged by the default rule.  So having rule that looks for traffic with FIN set and not logging it would prevent the default rule from seeing it to log.

            finset.png
            finset.png_thumb

            An intelligent man is sometimes forced to be drunk to spend time with his fools
            If you get confused: Listen to the Music Play
            Please don't Chat/PM me for help, unless mod related
            SG-4860 24.11 | Lab VMs 2.8, 24.11

            1 Reply Last reply Reply Quote 0
            • First post
              Last post
            Copyright 2025 Rubicon Communications LLC (Netgate). All rights reserved.