Lesson 13

Date: 6/28/2017
Linux Network Security
Linux System Administration


Closing ports

  • The open ports are related to the aplications/processes, which start either at the system startup or through inetd
    For the Systemd aware applications,
    
    systemctl stop service_name
    systemctl disable service_name
    

    To disable a port in inetd, modify /etc/inetd.conf file, commenting out the services, for example:
    
    # shell           stream  tcp     nowait  root    /usr/sbin/tcpd  /usr/sbin/in.rshd
    # login           stream  tcp     nowait  root    /usr/sbin/tcpd  /usr/sbin/in.rlogind
    # exec            stream  tcp     nowait  root    /usr/sbin/tcpd  /usr/sbin/in.rexecd
    
    Then make inetd daemon to re-read the configuration file:
    
    killall -HUP inetd
    


  • Vulnerable services:
    telnet, rsh, rcp, rexec, ftp, portmap, nfs, mountd, ypbind, ypserv.
    Disable them if your computer is on the open Internet. But if you need them, install a firewall and implement the tcp_wrappers.

  • Relatively secure services:
    Services protected with SSL libraries for encrypted connection such as SSH, LDAP, Apache; Kerberos.


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