From: Mike Tancsa (mikesentex.net)
Date: Mon Sep 08 2003 - 12:50:15 CDT

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At 06:08 PM 06/09/2003 +0400, 3APA3A wrote:

>The problem is, remote attacker can establish as much connections per
>minute as bandwidth allows... Now, guess how inetd reacts if more than
>256 connections received in one minute? It will disable service for next
>10 minutes to help attack to succeed. Of cause, this is documented.
>Interval is not configurable.
>
>something like
>
>Jul 23 15:27:10 host inetd[86]: ftp/tcp server failing (looping), service
>terminated
>
>will appear in logs... If connection is closed by attacker before
>service actually starts, IP address of attacker will never be logged.
>
>IV. Workaround

Hi,
On FreeBSD's inetd there is the -C option in conjunction with the -R option

      -C rate
              Specify the default maximum number of times a service can be
              invoked from a single IP address in one minute; the default is
              unlimited. May be overridden on a per-service basis with the
              "max-connections-per-ip-per-minute" parameter.

      -R rate
              Specify the maximum number of times a service can be invoked in
              one minute; the default is 256. A rate of 0 allows an unlimited
              number of invocations.

You can run without either of these options, but then you risk a DoS from
resource starvation. e.g. invoke 1000 copies of ftpd and eat up all the
RAM/Swap etc. Its problematic either way, but at least you can mitigate
the effects somewhat if its a single host attacking.

         ---Mike

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