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securing linux

what people can see. securing linux. Big Picture. How rob a bank. A bit of History. 1954 & 1960 Bell System Tech Journals, trunk routing and frequencies Pranks Wozniak called Pope 2600 Hz Tone Captain Crunch whistle Phone Phreaking

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securing linux

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  1. what people can see securing linux

  2. Big Picture How rob a bank

  3. A bit of History • 1954 & 1960 Bell System Tech Journals, trunk routing and frequencies • Pranks Wozniak called Pope • 2600 Hz Tone Captain Crunch whistle • Phone Phreaking • Steve Wozniak’s blue box tone generator • 1990 Phone system became digital • War dialing early form of scanning • Wargames 1983

  4. Socket Programming • USPS Addressing • 1520 Orchard Road Apt 2A • IP Addressing • 192.168.10.50/5900 • Service / Application listens on open port • Instance messaging, VOIP in Games, telnet, FTP, HHTP • Protocols – languages

  5. overview • Network topologies • eggshell architectures • where to get information • news groups and mailing lists • mapping a network • ping sweeps and traceroutes • mapping a host • port scans and OS fingerprinting • network scanners • everything in a single powerful package • social engineering • exploiting human nature

  6. where to get information • news groups and mailing lists • forums • WHOIS database • www.arin.org • DNS

  7. Traditional topology

  8. Enhanced traditional topology

  9. Secure network topology

  10. news groups / mailing lists / forums • these are valuable resources • system administrator • newbie • BUT people get over excited and reveal too much information (gear head syndrome) • golden rule - remain faceless and traceless • security through obscurity • post only using generic terms

  11. news groups / forums • they are a source of information • personal information • name, address, title, phone, e-mail • system configuration • network architecture • real host names and IP addresses • hardware: brand names and model numbers • archives • this information never goes away!!! • http://www.archive.org

  12. news groups / mailing lists • countermeasures: • use generic titles, not real names • use switchboard numbers, not personal numbers • separate e-mail address • work-related communication (generic title) • webadmin@cs.lewisu.edu • personal communication • smithpaul@cs.lewisu.edu • limit any public description of network • fictitious IP addresses & fictitious host names

  13. WHOIS databasewww.arin.org • whenever a URL is registered • information must be submitted with registration • this information is publicly available • whois utility • may require installation • linux example: • whois lewisu.edu • whois ibm.com

  14. WHOIS database • countermeasures: • use generic titles, not real names • use switchboard numbers, not personal numbers • separate e-mail address • work-related communication (generic title) • techdirector@cs.lewisu.edu • personal communication • smithpaul@cs.lewisu.edu • obviously you MUST give valid information • the goal is NOT to give away valuable information unnecessarily

  15. DNS issues • zone files have numerous options which provide information • HINFO system info: CPU and OS • TXT additional text • RP responsible person information • zone transfers • mandatory from primary server to secondary server

  16. DNS Basics • Domain name system performs ip to name resolutions on the internet • Started in 1983 RFC 882 has grown to one of the largest and most powerful parts of the net. • Other than name translation a number of protocols and applications use DNS for their main activity • SMTP for mapping email address to their server • SPF records, telephone numbers & addresses, certificates and other info stored in DNS zone records

  17. BIND • Berkeley Internet Name Domain Server • BIND is open-source software that implements the DNS protocols for the Internet.

  18. DNS issues • dig DNS lookup utility (domain information groper) is a flexible tool for interrogating DNS name servers. • linux example: • dig -t hinfo hostname • dig -t txt hostname

  19. DNS issues • reverse lookups (IP address --> URL) often provide too much free information • 129.42.58.216 --> www.ibm.com • www is a standard prefix for a web server • linux example: • dig www.lewisu.edu • dig -x 204.248.57.178

  20. DNS issues • every version of bind (4, 8, and 9) has its flaws! • 9 was a total rewrite and still had issues • the following command • host -c chaos -t txt version.bind <server> • will usually tell you the specific vesion • linux example: • dig -c chaos -t txt version.bind

  21. DNS issues • countermeasures: faceless & traceless • edit /etc/named.conf • delete HINFO records • delete TXT records • RP records should contain generic title • eliminate zone transfers • primary to secondary server • allow-transfer { 233.45.164.27; }; • otherwise • allow-transfer { none; }; • disable the version.bind response • version “not available”;

  22. protocols and services • network layer • IP: internet protocol • transport layer • ICMP: internet control message protocol • UDP: user datagram protocol • TCP: transmission control protocol • services

  23. IP: internet protocol • foundational layer for higher level protocols • packet header contains • source IP address • destination IP address

  24. ICMP: internet control message protocol • purpose of ICMP is to provide feedback about IP performance • packet header contains • source IP address, destination IP address • packet type, checksum, data • most well-known packet types • 7 echo request • 0 echo reply • 3 destination unreachable • 30 traceroute

  25. UDP: user datagram protocol • purpose of UDP is minimal transport service with no guarantee of delivery • connection-less • packet header contains • source IP address, destination IP address • source port number, destination port number • length, checksum, data • faster communication • but packet loss possible

  26. TCP: transmission control protocol • purpose of TCP is a transport service with guarantee of delivery • connection-oriented • packet header contains • source IP address, destination IP address • source port number, destination port number • sequence #, control bits, checksum, data • slower communication • but no packet loss

  27. TCP: transmission control protocol • control bits include: • SYN, ACK, RST, FIN, ... • building a connection: • source sends SYN • destination sends SYN/ACK • source sends ACK • terminating a connection: • source sends FIN/ACK • destination sends ACK • destination sends FIN/ACK • source sends ACK

  28. services • port numbers fall into three categories: • 0 through 1023 well-known • 1024 through 49151 registered • 49152 through 65535 dynamic / private • www.iana.org has responsibility for assigning well-known port numbers • well-known port numbers can only be used by root

  29. services • linux example: • less /etc/services

  30. mapping a network • ping sweeps • cracker sees what is out there? • traceroutes • cracker learns how to get there? • countermeasures

  31. ping sweeps • types of ping sweeps • icmp ping traditional echo request • echo port ping request to port 7 (echo) • fast ping icmp ping to multiple hosts • network sweep

  32. ping sweeps • countermeasures: • edit iptables and firewalls • no incoming / outgoing ICMP requests • limit ICMP requests to internal network only • drop ICMP at firewall • be sure echo port and chargen port are disabled • edit /etc/inetd.conf or /etc/xinetd.conf • consider disabling inetd or xinetd completely!

  33. fundamental network tools • netcat / nc • swiss army knife of network communication • invaluable to both • the system administrator • the cracker • nmap • basic tool for • ping sweeps • port scans

  34. ntop • ntop is a network traffic probe that shows network usage • similar to the UNIX top command • ntop is a daemon that monitors the network • ntop has a web interface

  35. traceroutes • once potential targets have been identified via ping sweeps, the cracker can augment information about the hosts using traceroute • often provides information regarding • location • ISP names and locations often visible • hardware • descriptive names for routers, switches, and hosts

  36. traceroutes • flavors • UNIX traceroute • command • traceroute <target> • sequence of UDP packets having increasing TTLs • Matt's traceroute • command • mtr <target> • sequence of ICMP packets having increasing TTLs

  37. traceroutes • countermeasures: • edit iptables and firewalls • drop ICMP request packets • drop UDP packets in traceroute range • 33,435 through 33,524 • do NOT use descriptive names for components within the network • function / role • vendor

  38. mapping a host • port scans • cracker sees what ports are open • OS fingerprinting • cracker determines underlying software • countermeasures

  39. port scans • what ports are open on the target host? • what daemon is listening on each open port? • what software? what version?

  40. port scans • tools • netcat • UDP scans • TCP scans • nmap • UDP scans • TCP scans • TCP stealth scans • strobe

  41. port scans • countermeasures: • klaxon • incorporated into /etc/inetd.conf or /etc/xinetd.conf • to listen on unused ports • scanlogd • monitors ports for sudden increase in activity • portsentry • monitors up to 64 ports • able to take action against an intruder! • tcp wrappers and/or iptables • psad • analysis of firewall logs

  42. port scans • identifying software listening on a given port is usually as simple as • telnet <target> <port> • software typically displays a banner announcing itself and its version number! • countermeasures: • remove / modify banner display • example: • in /etc/sendmail.cf • OsmtpGreetingMessage=$jUPS 2005;$b

  43. OS fingerprinting • OS fingerprinting • telnet is notorious for identifying • the operating system, the distribution, even the kernel • open ports often provide clues • smtp, ssh, and portmap => UNIX • netbios => Windows • /etc/issue, /etc/issue.net, and /etc/motd • often convey too much information

  44. OS fingerprinting • active OS fingerprinting • send sequence of special IP packets to target • catalog responses • compare with database of responses from various operating systems • software • queso • nmap • xprobe

  45. OS fingerprinting • countermeasures: • utilize a firewall in front of servers • operating system detected is that of firewall and not that of the server • disable ICMP packets at the firewall • negates xprobe • install IP Personality • only for Linux 2.4 kernels? • using iptables, can impersonate ANY operating system

  46. OS fingerprinting • passive OS fingerprinting • does not initiate any additional IP traffic • uses packet sniffing to gather information • software • siphon • pOf

  47. OS fingerprinting • countermeasures • can change some parameters of the operating system • cat /proc/sys/net/ipv4/ip_default_ttl • default value is 64 • echo 35 > /proc/sys/net/ipv4/ip_default_ttl • change to 35 • edit error messages masquerade as something else • apache httpd.conf

  48. network scanners • combine ping sweeps, traceroutes, port scans, and OS fingerprinting together and you have a • network scanner • ISS: Internet Security Scanner • first publicly available • NESSUS • the Cadillac of network scanners!

  49. network scanners • other network scanners • Nmap • SATAN: Security Administrator's Tool for Analyzing Networks • SANTA! • SAINT: Security Administrator's Integrated Network Tool • SARA: Security Auditor's Research Assistant • NSAT: Network Security Analysts Tool • text based! • raccess: Remote Access System • doesn't just check host; it exploits if possible!

  50. social engineering • ten common techniques of social engineering • impersonation • pretend to be some from inside the company to obtain passwords • usually coupled with research regarding IT personnel • sympathy • usually request access to hardware: server room or PC • usually coupled with dire consequences if unable to complete the task

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