CIT 380: Securing Computer Systems

1. CIT 380: Securing Computer Systems Malware CIT 380: Securing Computer Systems

2. Facebook • http://www.nku.edu/~frank/cit380/docs/facebook.htm CIT 380: Securing Computer Systems

3. Quarantine • http://www.nku.edu/~frank/cit380/docs/Quarantine.htm CIT 380: Securing Computer Systems

4. Morris Worm • First Internet Worm: November 1988 • Multi-architecture: Sun, VAX • Multi-vector • sendmail (debug backdoor) • fingerd (buffer overflow) • rsh (open .rhosts; password cracking) CIT 380: Securing Computer Systems

5. Morris Worm Spreading algorithm Local network topology: gateways, neighbors. Used users’ .rhosts, .forward files. Limited reinfection rate. Detection Avoidance Forged process listing as (sh). Removed created files quickly after use. CIT 380: Securing Computer Systems

6. Morris Worm Resource Requirements Disk Space. C compiler and linker. Network connection to parent computer. Problems Didn’t limit re-infections. Saturated CPU, network resources. CIT 380: Securing Computer Systems

7. Malware Self-Protection Anti-debugging Detect/disable debuggers when used to analyze code. Attack anti-malware tools Disable anti-malware tools upon infection. Kill processes or destroy/modify signatures. API checksums Avoid having UNIX/Win32 API calls in code. Store checksums of API names and search for match. CIT 380: Securing Computer Systems

8. Malware Self-Protection Code obfuscation Use unusual tricks and unused code to avoid dissassembly and prevent quick analysis of purpose. Self-modifying code. CIT 380: Securing Computer Systems

9. Self-Protection Compression Code looks almost random; size is smaller. Use unusual executable packers to avoid analysis. Data encryption Encrypt strings, hostnames, IP addresses to avoid detection. CIT 380: Securing Computer Systems

10. Self-Protection Embedding Use multiple levels of executable packers like UPX. Scanners have to understand and have time to parse and decompress each file format. CIT 380: Securing Computer Systems

11. Self-Protection Entry-Point Obscuring Changing initial code or entry point easy to notice. Alter program code to gain control randomly. Host morphing Alter host file during infection to prevent removal. CIT 380: Securing Computer Systems

12. Self-Protection: Encryption Encrypt all code except small decryptor. • Note that copy protected files will have similar decryptors to prevent analysis too. • Often uses multiple decryptors. • Change encryption key dynamically. Random Decryption Algorithm (RDA) • Choose random key for encryption. • Brute force search for key to decrypt. • Slows VMs/debuggers used for analysis. CIT 380: Securing Computer Systems

13. Self-Protection: Polymorphism Alter malware code with each infection. • Cannot be detected by signature scanning. • May alter decryptor only or entire code. • Insert junk instructions that do nothing. • Fragment and rearrange order of code. • Alternate sets of instructions for the same task. • Ex: SUB -1 instead of ADD 1 • Randomize names in macro viruses. CIT 380: Securing Computer Systems

14. Case Study: Zmist http://en.wikipedia.org/wiki/Zmist EPO, encrypted, polymorphic virus. Code integration Decompiles PE files to smallest elements. Inserts virus randomly into existing code. Rebuilds executable. Polymorphic decryptor Inserted as random fragments linked by JMPs. Randomizes self with ETG engine. CIT 380: Securing Computer Systems

15. Payloads Accidentally destructive. Replication damages data or exhausts system resources due to malware bugs. Ex: Morris Worm reinfected hosts, using all CPU. Nondestructive. Displays message, graphics, sound, or open CD door. Ex: Christma worm on IBM network in 1987. Destructive. Triggers randomly or on some event or machine type. Deletes files or overwrites data. Hardware destroyers: overwrite BIOS. CIT 380: Securing Computer Systems

16. Payloads Denial of Service Sometimes accidental due to high network use. Launch DDOS attack with all infected systems. Data Theft Phishing scams and spyware. Encryptors (ransomware) Encrypts user data. Ex: One_Half encrypts disk; enables access while running. Ex: AIDS Info: encrypts disk and holds for ransom. Spam Use network of infected systems to launder spam email. Ex: Sobig worm. CIT 380: Securing Computer Systems

17. Malware Interactions What happens when a virus infects a worm? Typically both propagate. May use each other’s self-protection techniques. What if anti-virus software removes a virus? Likely leaves unknown virus/worm alone. Partial removal can mutate the malware into a new form. CIT 380: Securing Computer Systems

18. Malware Interactions Competition and Parasitism Malware may remove competing malware. May exploit backdoors/RCI left by previous malware. May infect competing malware, hijacking its propagation. CIT 380: Securing Computer Systems

19. Theory of Malicious Code Theorem 1: It is undecidable whether an arbitrary program contains a computer virus. Proof: Define virus v as TM program that copies v to other parts of the tape, while not overwriting any part of v. Reduce to Halting Problem: T’ running code V’ reproduces V iff running T on V halts. Theorem 2: It is undecidable whether an arbitrary program contains malicious logic. CIT 380: Securing Computer Systems

20. Detecting Malware Signature-based • Look for known patterns in malicious code. • Defeated by polymorphic viruses. Smart scanning • Skips junk instructions inserted by poly engines. • Skips whitespace/case changes in macro viruses. CIT 380: Securing Computer Systems

21. Detecting Malware Decryption • Brute-forces simple XOR-based encryption. • Checks decrypted text against small virus sig to decide whether has plaintext or not. CIT 380: Securing Computer Systems

22. Detecting Malware Code Emulation • Execute potential malware on VM. • Scan VM memory after certain # iterations. • Watch instructions for decryptor profile. Code Optimization. • Optimize away junk instructions and odd techniques used by polymorphic viruses. CIT 380: Securing Computer Systems

23. Detecting Malware Heuristics • Code execution starts in last section. • Suspicious code redirection. • Suspicious section ACLs or size. • Suspicious library routine imports. • Hard-coded pointers into OS kernel. Neural Network Heuristics • IBM researchers trained neural net to recognize difficult polymorphic viruses. • Released in Symantec antivirus. CIT 380: Securing Computer Systems

24. Detecting Malware Behavior-based • Watch for known actions from malicious code. • Network access signature of worm. • Unexpected use of dangerous system calls. CIT 380: Securing Computer Systems

25. Detecting Malware Integrity Checking • Host-based Intrusion Detection System. • Record MAC, size, dates, ACL of files. • Periodically check for changes. • ex: Tripwire, AIDE, Osiris CIT 380: Securing Computer Systems

26. Defenses: Data vs. Code Separate data and instructions • Virus treats program as data • Writes self to file. • Virus treats program as instructions • Virus executes when program is run. • Solution: Treat all programs as data until trusted authority marks as executable. • Development difficult when compilers can’t produce executable code. CIT 380: Securing Computer Systems

27. Defenses: Information Flow Limit Information Flow • Virus executes with user’s identity. • Soln: Limit information flow between users. • Set flow distance to be one for users A, B, C. • A creates virus (fd=0), B executes it (fd=1). • C cannot execute B’s infected program (fd=2). • Indirect virus spread limited. • How can we track information flow? CIT 380: Securing Computer Systems

28. Defenses: Least Privilege Limit programs to least privilege needed example: SELinux Mail virus example • Virus arrives via email. • Virus exploits bug in email client to execute. • Virus saves self to file in Startup folder. • Virus infects Office documents. How least privilege would stop • Mail application cannot create virus binaries. • Mail application cannot write to Startup folder. • Mail application cannot write to Office documents. CIT 380: Securing Computer Systems

29. Defenses: Sandboxes Execute code in protected sandbox or VM. Virtual Browser Appliance Linux guest running Firefox under VMWare. Infections can only attack VM, not real host. Reset VM to initial state if infected. CIT 380: Securing Computer Systems

30. Defenses: Anomaly Detection Validate program actions with policy Limit access to system calls. Example: systrace. Check statistical characteristics. Programmer style. Compare source code with object. Statistics of write frequencies, program executions. CIT 380: Securing Computer Systems

31. Defenses: Counter-worms Worm that removes other worms from net. Nachi/Welchia • Multi-vector W32 worm • Nachi.A removes W32/Blaster worm • Nachi.B removes W32/MyDoom worm • Installed MSRPC DCOM patch to prevent future infections from Blaster. • Removes self after 2004. Side-effects • Infected Diebold ATMs • Worm traffic DOSed Internet, esp Microsoft. CIT 380: Securing Computer Systems

32. Fast Worms Slammer Worm Characteristics • Attacked MS SQL servers. • Worm is single 404-byte UDP packet. • Random-scan (PRNG bugs limited.) • Limited by network bandwidth, not latency. • Observed scan rate of 26,000 hosts/second. CIT 380: Securing Computer Systems

33. Fast Worms • Infected 90% of vulnerable hosts in 10 min. • Too fast for humans to react. • Shutdown 13,000 Bank of America ATMs due to compromising db servers, heavy traffic. CIT 380: Securing Computer Systems

34. Profitable Malware Sobig • W32 worm using email/network share vectors. • Contains upgrade mechanism • Worm checked sites every few minutes. • When site valid, downloaded code. • Later variants could update upgrade server list. • Downloaded payload from upgrade mechanism • Key logger. • Wingate proxy server (for spam proxying.) CIT 380: Securing Computer Systems

35. Profitable Malware Trojans Backdoor.Lala transfers authentication cookies for eBay, PayPal, etc. to maker. PWSteal.Bancos automates phishing by displaying fake web pages when browser goes to certain bank sites. Spyware and Adware More than ever using Trojan techniques. Win32/Bube virus exploits IE flaw and acts as a virus infecting IE, then downloads adware. CIT 380: Securing Computer Systems

36. Mobile Malware 2004: Cabir virus infecting Symbian OS mobile phones using Bluetooth appeared in June. 2005: Commwarrior-A worm spreads to Symbian series 60 phones via phone’s MMS. CIT 380: Securing Computer Systems

37. Mobile Malware Around a 1000 pieces of mobile malware exist. For Blackberries and Palm Pilots too. Expect more as smart phones become common. CIT 380: Securing Computer Systems

38. Offline Impact Davis-Besse nuclear power plant Slammer infected Plant Process Computer and Safety Parameter Display System (Jan 2003.) Analog backups unaffected. Infected contractor’s network, then moved through T1 line that bypassed plant firewall. Seattle 911 system Slammer disabled computer systems. Dispatchers reverted to manual systems. 2003 Blackout Blaster infected First Energy systems. CIT 380: Securing Computer Systems

39. Modern Malware is Stealthy: rootkit techniques common. Targeted: targets smaller banks and countries, leverages current events: • January: Storm Worm appears via email with subject “230 dead as storm batters Europe.” • February: Miami Dolphins Stadium site hacked before superbowl so that it would infect browsers with trojan that grabbed WoW data. Blended: combine trojan, virus, worm features. Web-based: use web for delivery and update. Profit-driven: the goal is to make money. CIT 380: Securing Computer Systems

40. References • Ross Anderson, Security Engineering, Wiley, 2001. • Matt Bishop, Computer Security: Art and Science, Addison-Wesley, 2003. • William Cheswick, Steven Bellovin, and Avriel Rubin, Firewalls and Internet Security, 2nd edition, 2003. • Fred Cohen, http://www.all.net/books/virus/part1.html, 1984. • Simson Garfinkel, Gene Spafford, and Alan Schartz, Practical UNIX and Internet Security, 3rd edition, O’Reilly & Associates, 2003. • Alexander Gostev, “Malware Evolution: January - March 2005,” http://www.viruslist.com/en/analysis?pubid=162454316, April 18 2005. • Elias Levy, “Crossover: Online Pests Plaguing the Offline World,” IEEE Security & Privacy, 2003. • Stuart McClure, Joel Scambray, George Kurtz, Hacking Exposed, 5th edition, McGraw-Hill, 2003. • Hilarie Orman, “The Morris Worm: A Fifteen-Year Perspective,” IEEE Security & Privacy, 2003 • Cyrus Peikari and Anton Chuvakin, Security Warrior, O’Reilly & Associates, 2003. • Ed Skoudis, Counter Hack Reloaded, Prentice Hall, 2006. • Ed Skoudis and Lenny Zeltser, Malware: Fighting Malicious Code, Prentice Hall, 2003. • Staniford, Stuart, Paxson, Vern, and Weaver, Nicholas, ‘How to 0wn the Internet in Your Spare Time,” Proceedings of the 11th USENIX Security Symposium, 2002 • Peter Szor, The Art of Computer Virus Research and Defense, Addison-Wesley, 2005. • Trend Micro, “1H2007 Threat Roundup,” http://us.trendmicro.com/imperia/md/content/us/pdf/threats/securitylibrary/1h_2007_threat_roundup_final_jul2007.pdf, 2007. CIT 380: Securing Computer Systems