Firewalls

1. SchwerpunktseminarSystemtechnik erstellt von Jörg Raiber Firewalls

2. Content • Introduction • Dangers • Attacks • The Firewall (general) • Firewall Techniques • Firewall Concepts • Computer Crime (statistics)

3. introduction • IT Security within the last 40 years • at the beginning security was controlled spatially (access to data processing center) and administrative (administrator, operator, user). • in the middle of the 70th the connection of data terminals determines the spatially insularity. • the development of the Home-PC shook the protective wall. • the fast development of networking till today‘s WWW was cause for security system „Firewall“.

4. The Internet – trigger of the danger • wherever we are, we are confronted with the internet. • more and more people are connected to the internet . • these days, companys and organisations have to connect to the internet and are attacked frequently. • we are not alone on the data highway and there is always the risk of incursion out of the net.

5. dangers: incursions • incursions • most frequent attack • allows the invader to use a computer system as if he is the legal user. • possibilities of access: • Social Engineering • guessing of username and password • special methodes without knowledge of username und password.

6. dangers: denial-of-service-attacks • denial-of-service attacks • aim: persons or groups should be embrassed to use their computers or special services. • means: overload of a running service • e.g.: flooding a werserver with requests • first significant attack was the „Morris Worm“. • 1999 e-mail-worm Melissa over MS-Outlook • feb. 2000 attack against Yahoo!, CNN, Amazon, eBay; recently W32.Blaster and Sobig.F • distributed denial-of-service-attack • distributed attack over serveral computers

7. dangers: information theft • attacker wants to get data. • attacker is able to steal data without breaking into the machine (redirection of target address). • active theft: • simulation of a valid computer or user. • passive theft: • tapping a network and waiting for interesting data.

8. attacks: scanning • scanning of ip-addresses • query the active ip-addresses of a network by means of the „ping“ instruction. • allows to determine the internal network structure. • scanning of users • finding out users by using „finger“ command. • scanning of services • attacker scans serveral ports to find out which services are running.

9. password-snooping andip-masquerade • password-snooping • listening of username and password • e.g. there is a risk to use ftp or telnet, because username and password are transmitted in plain text. • ip-masquerade • adopting a foreign ip-adress, which is valid inside the network to protect. • the characteristic of tcp/ip that erveryone is able to adopt every ip-address increases this risk.

10. hopping • hopping means the scipping from one remote host to another host inside the network to protect. • aim: using the possibilities of the remote host which are refused by direct connection. example

11. hopping: example Quelle: [Pohl01]

12. ip-spoofing • the attacker sends packets with wrong source address. • the faked address is valid into the network to protect. • acknowledgement is not sent to attacker. why this? • attacker is able to absorb the acknowledgement packets • attacker is not interested in acknowledgement (denial-of-service-attack) • attacker wants to injure others.

13. ICMP-attacks • ICMP is a component of TCP/IP • is a service for interchanging error and information messages inside the network. • messages: • echo request (ping) • echo response (response to ping) • fragmentation needed (smaller packets, please) • destination unreachable • redirect … • faked commands may manipulate.

14. The Firewall (general) • the firewall connects the unsafe network with the network to protect. • serveral components are scanning the communication data for: • communication type (FTP, telnet, HTTP, …) • communication participant • communication content (JavaScript, ActiveX, etc.) • limitates the communication according to the security policy.

15. Positioning the firewall • Almost, the firewall is installed at this point where the sensitive network is connected to the unsafe network (like the internet) • The result is, that whole traffic between the networks runs across the firewall.

16. General purposes of firewalls • Access control (network) • Which systems are allowed to communicate? • Access control (user) • Who is allowed to communicate? • Access control (data) • Which data can be sent? • Admission control • Which protocols and which services at which time? • Isolationg of services • Perpetuation of evidence and analysis • Alerting • Hiding of the internal network structure

17. Firewall-Techniques: Packet filter (1) • A packet filter routes IP-packets between the internal and the external network. • In addition to the normal routing-function, the packet-filter has to decide if he should transfer the packets, or not. • With this in mind there are specified packet filter roules which should help to decide. • Based on parsed packet headers the packet filter decides to transfer or block incoming packets.

18. Firewall-Techniques : Packet filter (2) • Selection is based on serveral information: • source address • target address • ports • ICMP-message-type • packetsize • Packet filter analyzes headers of Data-link-layer, Network-layer and Transport-layer of TCP/IP protocol stack. • The Application-layer is not parsed, which means limited possibilities of security.

19. Example packet filter

20. Filter roules • We are discerning between positive and negative roules: • positive: • It must explicitly be determined what should be allowd. All what is not determined is automatical forbidden. • negative: • Firstly, everything is allowed. With special entries we have to determine what should be forbidden. • Positive roules should be preferred, because forgotten prohibitions causes no risks.

21. Example-scenario • implemented rule:

22. ipchains (Linux) • With ipchains generated rules: ipchains –P input DENY ipchains –P output DENY ipchains –P forward DENY ipchains –A input –i eth0 –s 192.168.10.0/24 –d 172.16.51.50 –j ACCEPT ipchains –A input –i eth1 –s 172.16.51.50 –d 192.168.10.0/24 –j ACCEPT ipchains –A input –l –j DENY ipchains –A output –i eth1 –s 192.168.10.0/24 –d 172.16.51.50 –j ACCEPT ipchains –A output -i eth0 –s 172.16.51.50 –d 192.168.10.0/24 –j ACCEPT ipchains –A output –l –j DENY ipchains –A forward –b –s 172.16.51.50 –d 192.168.10.0/24 –j ACCEPT ipchains –A forward –l –j DENY

23. Application gateway with proxies (1) • Single-homed Application Gateway • one network interface only. • packets come and go across the same interface. • it consists the possibility to bypass the gateway. unsafe network sensitivenetwork

24. Application gateway with proxies (2) • Dual-homed Application Gateway • computer system with two network interfaces. • packets come thru the one and go thru the other interface. • gateway has total control of packets because there is no possibility to bypass him. unsafe network sensitivenetwork

25. Application gateway with proxies (3) • gateway decouples network logically and physikally. • gateway is ables to analyze the application layer. • configured as „dual-homed“, the gateway is the only computer system which is reachable from outside. Therefore he is extra worth to be protected. • this gateway is also named „Bastion“. • normally there are running one or servaral proxy services which manage communication substitutionally and transparently. • the proxies are able to estimate client requests for deciding, which requests they will leave out of consideration and which requests they will transfer.

26. Scheme application gateway

27. SMTP proxy • takes over e-mails on port 25 and after validation, he puts them down into a specific directory on the gateway. • a SMTP daemon checks incoming mail periodically and disposes the mail transfer agent (MTA) to forward it to the addressees. • MTA can not directly be addressed out of the unsafe network. • a common MTA is sendmail

28. Telnet proxy • is responsible for telnet communication • connection establishment happens over port 23 of the gateway. • user must identify and authenticate with specification of destination. • depending on user data special rights can be assigned or detracted. • after identification and authentication, the proxy establishes the connection with destination.

29. FTP proxy • is responsible for FTP connection • connection establishment happens over port 21 of the gateway. • user must identify and authenticate. • the FTP proxy disponses of some filter rules like: • command-filter ( cd: yes, del: no ) • data-filter ( *.jpg: yes, *.exe: no )

30. HTTP proxy • is responsible for HTTP connection. • connection establishment happens over port 80. • user-authentication is possible • disponses of some filters like: • command-filter ( FTP?, SMTP? ) • data-filter ( e.g. defined URLs only ) • „content security“ ( applet-filter, malware-filter)

31. Network Address Translation (NAT) • is a method to turn private (internal) IP addresses to public (external) IP addresses. • at sending the NAT router modifies source address into a valid external address; at receiving he retransforms it into a valid internal address.

32. Network Address Translation (2) • source-NAT (SNAT) = modifies the source address • destination-NAT (DNAT) = modifies the destination address • NAT router has to memorize the assigned addresses and keeps them in special tables. • port and address translation (PAT) translates also the ports NAT PAT external internal

33. Network Address Translation (3) • field of application: • internetconnection of multiple computers with only one public IP address. • scimping on IP addresses (shortness) • protective function (only „NAT machine“ is visible) • security features: • control of outgoing traffic • all traffic goes thru NAT router. • control of incoming traffic • only incoming connections allowed which are initiated by the router. • internal network structure is hidden.

34. firewall concepts (1) • exclusive use of packet filter: • allows and denys connection by checking source and destination address (MAC and IP). • limitatation of protocols (TCP, UDP, …) • limitation of ports and services • definition of timeslots • inadvisable for coupling sensitive network and internet. • exertion inside the intranet advisable.

35. firewall concepts (2) • exclusive use of application gateways: • allows and denys connection by checking source IP address and destination IP address. • admission control on user level • limitation of protocols • limitation of services • definition of timeslots • limitation of commands, user data and files (application layer) • perpetuation of evidence and recording possible (logfile) • alerting of security management possible • … • inadvisable for coupling sensitive network and internet. • exertion inside the intranet advisable.

36. firewall concepts (3) • combination of packet filter and und single-homed AG • two variations: • packet filter before AG (A) • packet filter behind AG (B) • A: • can be configured so that communication out of the unsave network works across the gateway only. • from the unsave network, only the gateway is visible. • the gateway adduces the most important security services. • caution: if an invader gets access to the gateway he may be capable to get access to all systems in the network.

37. firewall concepts (4) • B: • can be configured so that communication out of the sensitive network works across the gateway only. • from the sensitive network, only the gateway is visible. • the gateway adduces the most important security services. • the application gateway must be extra resistant against attacks. • inadvisable for coupling sensitive network and internet. • might be used for separation of sensitive organisation departments inside the intranet.

38. firewall concepts (5) • combination of packet filter and dual-homed AG • is characterized by series connection of packet filter and application gateway. • there are two variations of logical arrangement. • there is no way to bypass the application gateway. Both components contributes for security. • variation C is to prefer.

39. firewall concepts (6) • screened subnet and single-homed AG • screened subnet: • is an isolated decoupled subnet between sensitive and unsave network. • is already equipped with two packet filters. • is also described as De-Militarised-Zone (DMZ) . • computer systems inside the screened subnet are protected from both sides.

40. firewall concepts (7) • the two packet filters are adducing the most important security services. • the appication gateway allocates additional security services. • inadvisable for coupling sensitive network and internet. • might be used for separation of sensitive organisation departments inside the intranet.

41. firewall concepts (8) • screened subnet and dual-homed AG • is also called High-Level-Secirity-Firewall. • series connection of two packet filtersand one application gateway. • both components are monitoringcommunication. • No possibility to bypass theapplication gateway.

42. firewall concepts (9) • quality characteristic of High-Level-Security-Firewall: • simple rules • mutual protection • packet filter protects application gateway • nested security • serveral hindrances: packet filter  AG  packet filter • various operating systems • particular components can be managed from serveral operation systems. • multiple option of analysis • all layers of TCP/IP can be inspected. • is suitable for coupling sensitive network and internet.

43. final decision of firewall concept • an important measure before making a decision is to specify requirement of protection. • Matrix (basis: BSI)

44. computer crime – facts and numbers • contains all criminal acts which contains features of electronic data processing (EDP). • in addition to it, computer crime contains criminal acts where is used IT for planning, preparation and execution. • to this form of crime the BKA creates an update yearly.

45. quantum of computer crime • number of cases: • 6.507.394 criminal acts, 57.490 (0,88%) computer crime. regression of 27,5 percents. • committers: • 78,1% male • not german: 16,2 % • 31% under 21 years old • financial demage: • ca. 85 Mio. €

46. trend of computer crime • apart from computer sabotage and software piracy there is an regression of computer crime. • this also results from use of personal firewalls.

47. synoptical table of criminal acts

48. Thank you for attention!