IPv6 Security: Pembatasan Akses

Banyak layanan menggunakan library tcp_wrapper untuk kontrol akses.

22.8. tcp_wrapper

tcp_wrapper is a library which can help you to protect service against misuse. 22.8.1. Filtering capabilities

You can use tcp_wrapper for

   Filtering against source addresses (IPv4 or IPv6)

   Filtering against users (requires a running ident daemon on the client)

22.8.2. Which program uses tcp_wrapper

Following are known:

   Each service which is called by xinetd (if xinetd is compiled using tcp_wrapper library)

   sshd (if compiled using tcp_wrapper)

22.8.3. Usage

tcp_wrapper is controlled by two files name /etc/hosts.allow and /etc/hosts.deny. For more information see

$ man hosts.allow

22.8.3.1. Example for /etc/hosts.allow

In this file, each service which should be positive filtered (means connects are accepted) need a line.

sshd: 1.2.3. [2001:0db8:100:200::]/64 daytime-stream: 1.2.3. [2001:0db8:100:200::]/64

Note: there are broken implementations around, which uses following broken IPv6 network description: [2001:0db8:100:200::/64]. Hopefully, such versions will be fixed soon. 22.8.3.2. Example for /etc/hosts.deny

This file contains all negative filter entries and should normally deny the rest using

ALL: ALL

If this node is a more sensible one you can replace the standard line above with this one, but this can cause a DoS attack (load of mailer and spool directory), if too many connects were made in short time. Perhaps a logwatch is better for such issues.

ALL: ALL: spawn (echo "Attempt from %h %a to %d at `date`"

| tee -a /var/log/tcp.deny.log | mail root@localhost)

22.8.4. Logging

Depending on the entry in the syslog daemon configuration file /etc/syslog.conf the tcp_wrapper logs normally into /var/log/secure. 22.8.4.1. Refused connection

A refused connection via IPv4 to an xinetd covered daytime service produces a line like following example

Jan 2 20:40:44 gate xinetd-ipv6[12346]: FAIL: daytime-stream libwrap ¬ from=::ffff:1.2.3.4 Jan 2 20:32:06 gate xinetd-ipv6[12346]: FAIL: daytime-stream libwrap

from=2001:0db8:100:200::212:34ff:fe12:3456

A refused connection via IPv4 to an dual-listen sshd produces a line like following example

Jan 2 20:24:17 gate sshd[12345]: refused connect from ::ffff:1.2.3.4 ¬ (::ffff:1.2.3.4) Jan 2 20:39:33 gate sshd[12345]: refused connect

from 2001:0db8:100:200::212:34ff:fe12:3456

¬ (2001:0db8:100:200::212:34ff:fe12:3456)

22.8.4.2. Permitted connection

A permitted connection via IPv4 to an xinetd covered daytime service produces a line like following example

Jan 2 20:37:50 gate xinetd-ipv6[12346]: START: daytime-stream pid=0 ¬ from=::ffff:1.2.3.4 Jan 2 20:37:56 gate xinetd-ipv6[12346]: START: daytime-stream pid=0

from=2001:0db8:100:200::212:34ff:fe12:3456

A permitted connection via IPv4 to an dual-listen sshd produces a line like following example

Jan 2 20:43:10 gate sshd[21975]: Accepted password for user from ::ffff:1.2.3.4 ¬ port 33381 ssh2 Jan 2 20:42:19 gate sshd[12345]: Accepted password for user

from 2001:0db8:100:200::212:34ff:fe12:3456 port 33380 ssh2

Referensi

• http://www.tldp.org/HOWTO/Linux+IPv6-HOWTO/hints-daemons-tcpwrapper.html