Lecture 19 - Network Security

Transcription

1 Lecture 19 - Network Security CMPSC Spring 2012 Introduction Computer and Network Security Professor Jaeger

2 Exploiting the network... The Internet is extremely vulnerable to attack it is a huge open system... which adheres to the end-to-end principle smart end-points, dumb network Can you think of any large-scale attacks that would be enabled by this setup? 2

3 Malware Malware - software that exhibits malicious behavior (typically manifest on user system) virus - self-replicating code, typically transferring by shared media, filesystems, , etc. worm - self propagating program that travels over the network The behaviors are as wide ranging as imagination backdoor - hidden entry point into system that allows quick access to elevated privileges rootkit - system replacement that hides adversary behavior key logger - program that monitors, records, and potentially transmits keyboard input to adversary trojan - malicious software disguised as legitimate program 3

4 Worms A worm is a self-propagating program. As relevant to this discussion 1. Exploits some vulnerability on a target host 2. (often) embeds itself into a host 3. Searches for other vulnerable hosts 4. Goto (1) Q: Why do we care? 4

5 The Danger What makes worms so dangerous is that infection grows at an exponential rate A simple model: s (search) is the time it takes to find vulnerable host i (infect) is the time is take to infect a host Assume that t=0 is the worm outbreak, the number of hosts at t=j is 2 (j/(s+i)) For example, if (s+i = 1), how many hosts are compromised at time t=32? 5

6 The result 5,000,000,000 4,500,000,000 4,000,000,000 3,500,000,000 3,000,000,000 2,500,000,000 2,000,000,000 1,500,000,000 point of criticality 1,000,000, ,000,

7 The Morris Worm Robert Morris, a 23 year old doctoral student from Cornell Wrote a small (99 line) program November 3rd, 1988 Simply disabled the Internet How it did it Reads /etc/password, they tries the obvious choices and dictionary, /usr/dict words Used local /etc/hosts.equiv,.rhosts,.forward to identify hosts that are related Tries cracked passwords at related hosts (if necessary) Uses whatever services are available to compromise other hosts Scanned local interfaces for network information Covered its tracks (set is own process name to sh, prevented accurate cores, re-forked itself) 7

8 Code Red Anatomy of a worm: Maiffret (good reading) Exploited a Microsoft IIS web-server vulnerability A vanilla buffer overflow (allows adversary to run code) Scans for vulnerabilities over random IP addresses Sometimes would deface the served website July 16th, outbreak CRv1- contained bad randomness (fixed IPs searched) CRv2 - fixed the randomness, added DDOS of Turned itself off and on (on 1st and 16th of month) August 4 - Code Red II Different code base, same exploit Added local scanning (biased randomness to local IPs) Killed itself in October of

9 Worms and infection The effectiveness of a worm is determined by how good it is at identifying vulnerable machines Morris used local information at the host Code Red used what? Multi-vector worms use lots of ways to infect E.g., network, DFS partitions, , drive by downloads Another worm, Nimda did this Lots of scanning strategies Signpost scanning (using local information, e.g., Morris) Random IP - good, but waste a lot of time scanning dark or unreachable addresses (e.g., Code Red) Local scanning - biased randomness Permutation scanning - instance is given part of IP space 9

10 Other scanning strategies Hit-list scanning Setup - use low and slow scanning to determine which hosts are vulnerable (i.e., create a hit list) Start the worm, passing the list of vulnerable hosts, reduce/ device the list at each host Gets past the slow start part, gets right into the exponential Essentially removes the window to stop worm 5,000,000,000 4,500,000,000 4,000,000,000 3,500,000,000 3,000,000,000 2,500,000,000 2,000,000,000 1,500,000,000 1,000,000, ,000,

11 Other scanning strategies The doomsday worm: a flash worm Create a hit list of all vulnerable hosts Staniford et al. argue this is feasible Would contain a 48MB list Do the infect and split approach Use a zero-day vulnerability 11

12 Worms: Defense Strategies (Auto) patch your systems: most, if not all, large worm outbreaks have exploited known vulnerabilities (with patches) Heterogeneity: use more than one vendor for your networks Shield (Ross): provides filtering for known vulnerabilities, such that they are protected immediately (analog to virus scanning) Shield Network Traffic Network Interface Operating System Filtering: look for unnecessary or unusual communication patterns, then drop them on the floor This is the dominant method, getting sophisticated (Arbor Networks) 12

13 Advanced Methods Quarantine - how do stop it once it is out? Internet Quarantine: Requirements for Containing Self- Propagating Code. David Moore, Colleen Shannon, Geoffrey M. Voelker, Stefan Savage Assume you have a LAN/WAN environment We have already talked about how to prevent Q1: How do you recognize a worm? Q2: How do you stop a worm? Much work in this area... number of new addresses contacted number of incomplete IP handshakes number of connections to new local hosts (COI?) 13

14 Botnet Story 14

15 Botnets A botnet is a network of software robots (bots) run on zombie machines which run are controlled by command and control networks IRCbots - command and control over IRC Bot herder - owner/controller of network "scrumping" - stealing resources from a computer Surprising Factoid: the IRC server is exposed. 15

16 Statistics (controversial) The actual number of bots, the size of the botnets and the activity is highly controversial. As of 2005/6: hundreds of thousands of bots 1/4 of hosts are now part of bot-nets Growing fast (many more bots) Assertion: botnets are getting smaller(?!?) 16

17 What are botnets being used for? piracy mining attacks hosting Activities we have seen Stealing CD Keys: 50 botnets PRIVMSG #atta :BGR $getcdkeys BGR ,000 PRIVMSG #atta :Microsoft Windows Product ID bots/net CD Key: ( ). BGR PRIVMSG #atta :[CDKEYS]: Search completed. Clients/servers spread around the world Reading a user's clipboard: B][[email protected] PRIVMSG ##chem## :~getclip Ch3m [email protected] PRIVMSG ##chem## :- [Clipboard Data]- Ch3m [email protected] PRIVMSG ##chem## :If You think the refs screwed the seahawks over put your name down!!! Different geographic concentrations DDoS someone: [email protected] PRIVMSG #t3rr0r0fc1a :!pflood s7n 2K503827!s7s@ PRIVMSG #t3rr0r0fc1a :\002Packets\002 \002D\002one \002;\002>\n s7n 2K503827!s7s@ PRIVMSG #t3rr0r0fc1a flooding...\n Set up a web-server (presumably for phishing): [DeXTeR]!alexo@l broadband.actcom.net.il PRIVMSG [Del]29466 :.http 7564 c:\\ [Del][email protected] PRIVMSG _[DeXTeR] :[HTTPD]: Server listening on IP: :7564, Directory: c:\\. 17

18 IRC one-to-many or many-to-many chat (for BBS) Client/server -- TCP Port 6667 Used to report on 1991 Soviet coup attempt Channels (sometimes password protected) are used to communicate between parties. Invisible mode (no list, not known) Invite only (must be invited to participate) Server Server Server Server Server 18

19 IRC botnets An army of compromised hosts ( bots ) coordinated via a command and control center (C&C). The perpetrator is usually called a botmaster. IRC Server Find and infect more machines! Bots (Zombies) A botnet is comparable to compulsory military service for windows boxes -- Bjorn Stromberg 19

20 Typical (IRC) infection cycle optional Bots usually require some form of authentication from their botmaster 20

21 Infection Worms, Trojan horses, backdoors Note: the software on these systems is updated Bot theft: bot controllers penetrate/"steal" bots. 21

22 Not only for launching attacks... Some botmasters pay very close attention to their bots hence covert infiltration is important In many cases, Botmasters inspect their bots fairly regularly, and isolate certain bots ( cherry picking ) #HINDI-FILMZ :#1 294x [698M] [Movie] Dil Bechara Pyar Ka Mara DvD-RiP [ Full / AVI / 2001 ] #HINDI-FILMZ :#2 126x [141K] [English Subtitles] Dil Bechara Pyar Ka Mara #HINDI-FILMZ :** 2 packs ** 3 of 3 slots open, Record: 45.3KB/s #HINDI-FILMZ :** Bandwidth Usage ** Current: 0.0KB/s, Record: 304.5KB/s #HINDI-FILMZ :** To request a file type: /"/msg [HF]-[Street-Hunk]-30 xdcc send #x/" ** #HINDI-FILMZ :** -= #Hindi-Filmz=- ** #HINDI-FILMZ :** I M 100% Desi!! ** #HINDI-FILMZ :Total Offered: MB Total Transferred: GB That s a lot of movies served! ( ~ 300) 22

23 Measuring botnet size Two main categories Indirect methods: inferring botnet size by exploiting the side-effects of botnet activity (e.g., DNS requests) Direct methods: exploiting internal information from monitoring botnet activity 23

24 How many bots? Approach: infiltration templates based on collected honeynet data, e.g., observing compromised hosts that are identified within the channel How many? 1.1 million distinct user IDs used 425 thousand distinct IP addresses Issues: NAT/DHCP? Cloaked IP address (SOCKS proxies?) Botnet membership overlap 24

25 Botnet size, what does it mean? Infection Footprint: the total number of infected bots throughout a botnet s lifetime Relevance: how wide spread the botnet infection Effective Botnet Size: the number of bots simultaneously connected to the command and control channel Relevance: the botnet capacity to execute botmaster commands (e.g., flood attacks) An Example: While a botnet appeared to have a footprint of 45,000 bots, the number of online bots (i.e. its effective size) was < 3,000 25

26 Take away Internet malware is used to gain control of hosts Lots of them potentially Worms: self-propagating malware Lifecycle Find, Infect, Propagate Zero-day Botnets Network of zombies under command and control Used for a variety of malicious purposes Key concern: botnet size 26