COMMAND

    inetd

SYSTEMS AFFECTED

    Linux

PROBLEM

    Zo0mer posted following.  He found local DoS that crashes  telnetd
    (tested on Slackware 4.0, RH 5.2).  Type:

        telnet localhost | telnet localhost | telnet localhost ......

    about 50 times result will be 'Connection Refused', telnetd crash.
    This was  tested on  Debian 2.1  and it  crashes there  too.  This
    however is inetd problem:

        Sep  9 17:55:05 server inetd[186]: telnet/tcp server failing (looping),
        service terminated
        Sep  9 17:55:28 server inetd[186]: auth/tcp server failing (looping),
        service terminated

    So,  what  this  does  is  get  the  telnetd service kicked out by
    inetd..by using a similar method with numerous rapid  connections,
    you can shut-down any tcp  service running under inetd, ie.  ftpd,
    identd,  etc,  just  by  connecting  to  the  port each service is
    listening on.

SOLUTION

    Until a fix  is out, it  might be wise  to crontab a  HUP to inetd
    every  few  minutes,  so  that  if  somebody takes out your telnet
    service,  you  can  log  back  in  eventually.   The default is to
    shutdown the service if more than 40 instances are started in a 60
    second period.  *Any* service  under inetd will halt if  more than
    the max  number of  instances are  started.   Change this  line in
    inetd.conf:

        telnet stream  tcp     nowait  root    /usr/sbin/tcpd  in.telnetd

    To:

        telnet stream tcp   nowait.256 root	/usr/sbin/tcpd in.telnetd