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Improving the security of xinetd System
The xinetd package used by Panther provides a number of security features, including the ability to finely control access based on source IP address and time of access. It features extensive logging, and also provides some protection from denial of service attacks. Global defaults for all services launched through xinetd are configured in the file /etc/xinetd.conf. Use man xinetd.conf for more information:
        instances               = 60
        log_type                = SYSLOG daemon
        log_on_success          = HOST PID
        log_on_failure          = HOST
        cps                     = 25 30
includedir /etc/xinetd.d
The first configuration option, instances, specifies the maximum number of connections permitted for any one service. This can be used to protect the system from certain types of denial of service attacks. The value chosen will depend on the available system resources and bandwidth. Another denial of service protection mechanism is to limit the number of connections from a single host. To enable this functionality, add the following line to the configuration (just below cps = 25 30):
per_source		= 10
This will limit each host to only 10 connections per service. By default, xinetd accepts connections from all hosts; to change this behaviour, add the line:
only_from		=
to the configuration options. This will deny access to all hosts for all services, by default. The hosts permitted to connect to specific services will have to be configured in each of those services' configuration settings.

xinetd uses separate configuration files to define the behaviour of each service it supports. The settings in the server specific configuration files override the behaviour specified in the global file. These are found in the /etc/xinetd.d directory. For example, to permit access from and to the SSH (remote login) service, edit the /etc/xinetd.d/ssh file:
service ssh
        disable = no
        socket_type     = stream
        wait            = no
        user            = root
        server          = /usr/libexec/sshd-keygen-wrapper
        server_args     = -i
        groups          = yes
        flags           = REUSE IPv6
        session_create  = yes
And add the lines (just after the line session_create = yes):
only_from		=
If any hosts are to be explicitly denied access, the no_access setting can be used, for example:
no_access		=
It is also possible to add networks instead of individual IP addresses to either of the configuration settings mentioned above. These can be specified in a number of formats (see the xinetd.conf man page for more details). Any settings specified in service specific configuration files override the global settings specified in /etc/xinetd.conf. For example, to override the default maximum number of instances of SSH, add the line:
instances		= 8
Note: By default, Mac OS X enables IP version 6 on all network services started through the xinetd service, but since the IP addresses specified above are in IPv4 notation, they will not work as expected. It is necessary to disable IPv6 compatibility on all network services where access controls are specified using the IPv4 notation. This is done, by removing the string IPv6 from the line:
flags    = REUSE IPv6
from each service's configuration file. Restart the xinetd process for the changes to the configuration files to take effect.

This hint is an exerpt from a guide I wrote to securing Mac OS X, which is available from Corsaire Ltd's White Paper section. Disclaimer: I work for Corsaire, but this report is freely available.

[robg adds: I've downloaded the white paper, but haven't yet read much of it at all. It looks to be quite thorough, and as noted, it's free...]

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Improving the security of xinetd
Authored by: Accura on Jul 22, '04 07:43:42PM

Sweet hint, thanks


"The time has come," the walrus said. "To talk of many things..."

[ Reply to This | # ]
Improving the security of xinetd
Authored by: yellow on Jul 23, '04 02:37:00PM

Nice White Paper, BTW.

Care to expand it a little by delving into the world of PAM? In corporate situations it's nice to know when there are multiple failed logins, currently they aren't logged anywhere. Plus a multiple failed password attempt lockout would be sweet.

Anyway, great WP!

[ Reply to This | # ]
removing IPv6 could cause trouble
Authored by: cilly on Jul 23, '04 03:21:23PM

There is one thing I can not agree with this report, to remove IPv6 from the flag.

It depends on the service, i.e. FakeIdentd needs the flag IPv6, without that flag the service won't launch at all.

cilly @

[ Reply to This | # ]
removing IPv6 could cause trouble
Authored by: stephendv on Jul 25, '04 12:02:41PM

Yes, I agree that it depends on the service - and in what notation you're specifying access controls. If you're using IPv4 notation to lock down services, then the IPv6 flag must be disabled. I haven't yet tried enabling IPv6 and using v6 addresses to specify the access controls, but I'd expect this to work.

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Improving the security of xinetd
Authored by: icedtrip on Jul 24, '04 04:48:41PM
This along with many other Mac OS X security tweaks can be found in the following white paper.

Click Here

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