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Network Access Control

Network Access Control. Focus Question. What are three ways in which network security can be applied through the application layer?. Network Interfaces. Configuration files: /etc/sysconfig/network-scripts/ifcfg-* All interfaces are brought up with: /etc/init.d/network [start | restart]

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Network Access Control

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  1. Network Access Control

  2. Focus Question What are three ways in which network security can be applied through the application layer?

  3. Network Interfaces • Configuration files:/etc/sysconfig/network-scripts/ifcfg-* • All interfaces are brought up with:/etc/init.d/network [start | restart] • Individual interfaces managed with:/sbin/ifup eth?, /sbin/ifdown eth? • Interfacers turned on or off with:/sbin/ifconfig eth? [up|down]

  4. Application Config Files • sshd: /etc/ssh/sshd_config • httpd: /etc/httpd/conf/httpd.conf • vsftpd:/etc/vsftpd/vsftpd.conf • Xorg: xhosts and .Xauthority

  5. Libwrap.so • Three stages of access checking • Is access explicity permitted? • Is access explicity denied? • Otherwise, permit access! • Configuration store in two files: • Permissions in /etc/hosts.allow • Denials in /etc/hosts.deny • Basic Syntaxdaemon_list: client_list [:options]

  6. Daemon Specification • Daemon name: • Applications pass name of executable • Multiple services can be specified • Use wildcard ALL to match all daemons • Limitations for RPC daemons • Advanced Syntax:daemon@host: client_list …

  7. Client Specification • Host specification • by IP address (192.168.0.1 10.0.0.) • by name (www.redhat.com, .example.com) • by netmask (192.168.0.0/255.255.255.0) • by network name (/etc/networks or NIS)

  8. Advanced Client Syntax • Wildcards • ALL, LOCAL • KNOWN, UNKNOWN, PARANOID • EXCEPT operator • Can be used for client and service list • Can be nested

  9. Example • Consider the following example for the machine 192.168.0.254 • /etc/hosts.allow vsftpd: 192.168.0.in.telnetd, portmap: 192.168.0.8 • /etc/hosts.denyALL: .cracker.org EXCEPT trusted.cracker.org vsftpd, portmap: ALL sshd: 192.168.0. EXCEPT 192.168.0.4

  10. Questions and Observations • Only stations of the local network can FTP to the machine. • Only station 8 could NFS mount a remote directory. • All hosts on cracker.org except trusted.cracker.org are denied access to any tcp-wrapped services. • Only the host 192.168.0.4 is able to ssh in from local nw. • What stations from the local network can initiate atelnet connection? • Can machines in the cracker.org network access the web server? • What tcp-wrapped services are available to a system from someother.net? • What’s wrong with these rules from the perspective of a security policy?

  11. Network Attacks • Header abusespackets that contain maliciously constructed, broken, or falsified network layer headers. • Network stack exploitsexploit a vulnerability in the networks stack implementation. • Bandwidth saturationpackets that are designed to saturateall available bandwidth on a targeted network.

  12. Attack Responses • A filtering operationconducted by a device such as a firewall or a router to block the source IP address of attacker. • Reconfiguration of a routing protocolroute blackholing • Applying threshold logicto the amount of traffic that is allowed to pass through a firewall or router based on bandwidth.

  13. Review

  14. Focus Question What are three ways in which network security can be applied through the application layer? • Most modern network applications allow some security and access control to be configured in their own configuration files. • Common Libraries like libwrap.so can be linked into applications to allow access control to be configured. • Network services may be managed by super-daemons, like xinetd which can support a variety of access controls.

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