CSC 482/582: Computer Security Malware CSC 482/582: Computer Security

Topics Types of Malware Self-Protection Mechanisms. Payloads. Trojan Horses Viruses Worms Backdoors Rootkits Self-Protection Mechanisms. Payloads. Malware Interactions. Detecting Malware. Defending against Malware. The changing Malware environment. CSC 482/582: Computer Security

Types of Malware Trojan Horse Virus Worm Backdoors Tricks user into executing malicious code. Virus When run by user, 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 482/582: Computer Security

What about Spyware? Malware by any other name… Corporate malware. Presents legal issues for anti-malware software. CSC 482/582: Computer Security

Trojan Horse Attacker: Victim: cat >ls cp /bin/sh /tmp/.xxsh chmod u+s,o+x /tmp/.xxsh rm ./ls ls $* ^D Victim: ls Program with both an overt and covert effect Displays expected behavior when user executes. Covert effect (executed with user’s privileges) violates security policy. CSC 482/582: Computer Security

Virus Self-replicating code Virus Pseudocode: 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 482/582: Computer Security

Types of Viruses Boot Sector Executable Dynamic Library When system boots, code in boot sector executed. Propagate by altering boot disk creation. Uncommon today because of low use of boot floppies, but some Vista laptops shipped with one. Executable Infects executable programs (e.g., COM, EXE). Executes when infected program is run. Virus usually runs first, then runs original code. Dynamic Library Infected dynamicly linked libraries (DLLs.) Executed when any program uses infected DLL. CSC 482/582: Computer Security

Types of Viruses Device Driver Virtual Machine (.NET) Infects loadable device driver. Executes in kernel mode. Virtual Machine (.NET) Infects .NET MSIL binaries. Portable: compiled to native code by CLR. Archive Infectors Inserts Trojan horse into ZIP files. Uses social engineering techniques to get user to run. CSC 482/582: Computer Security

Types of Viruses 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 482/582: Computer Security

Infection Methods Overwriting Appending Prepending Overwrites program code with virus. Breaks infected program. Appending Append virus code to executable. Insert JMP at beginning of executable. Prepending Insert virus code at beginning of executable. Shift original code to follow virus. CSC 482/582: Computer Security

Infection Methods Parasitic Cavity Fractionated Cavity Inserts virus code at beginning of executable. Shifts beginning of program to end of file. Cavity Insert virus code into unused blocks of file. Insert JMP at beginning of executable. Fractionated Cavity Fragment virus; inject into multiple cavities. Loader reads fragments into continuous memory. CSC 482/582: Computer Security

Infection Methods Compressing Fragmenting Companion Compresses executable to make space. Inserts virus and decompression code. Fragmenting Dynamically fragment virus. Insert fragments by overwriting or shifting code. Fragments JMP/CALL each other. Companion Infects COM file of same name as EXE file. Infects alternate data stream of Win32 file. CSC 482/582: Computer Security

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 482/582: Computer Security

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 Sep 2001 Removed Code Red II and patched vulnerability. Slammer Jan 2003 SQL Server worm infected entire Internet <1 hr. Sobig Jun 2003 Spam zombie botnet; RCI. CSC 482/582: Computer Security

Worm Components Vector Propagation Engine Target Selection Scanning Engine Payload CSC 482/582: Computer Security

Vector Software to gain access to target host. Common vectors: Buffer overflow exploits. Network file sharing, both NFS/SMB and P2P. Social-engineering via email or IM. Weak passwords. Parasitism: target backdoors and worm flaws. CSC 482/582: Computer Security

Propagation Engine Transfers worm to host exploited by vector. Small worms like Slammer included in vector. Worm Propagation Methods: FTP HTTP SMB TFTP CSC 482/582: Computer Security

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 482/582: Computer Security

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 482/582: Computer Security

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 482/582: Computer Security

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 482/582: Computer Security

Morris Worm Spreading algorithm Detection Avoidance 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 482/582: Computer Security

Morris Worm Resource Requirements Problems Disk Space. C compiler and linker. Network connection to parent computer. Problems Didn’t limit re-infections. Saturated CPU, network resources. CSC 482/582: Computer Security

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. Code obfuscation Use unusual tricks and unused code to avoid dissassembly and prevent quick analysis of purpose. Self-modifying code. CSC 482/582: Computer Security

Self-Protection Compression Data encryption Embedding 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 Use multiple levels of executable packers like UPX. Scanners have to understand and have time to parse and decompress each file format. CSC 482/582: Computer Security

Self-Protection Entry-Point Obscuring Host morphing 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 482/582: Computer Security

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 482/582: Computer Security

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 482/582: Computer Security

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 482/582: Computer Security

Payloads Accidentally destructive. Nondestructive. 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 482/582: Computer Security

Payloads Denial of Service Data Theft Encryptors (ransomware) Spam 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. CSC 482/582: Computer Security

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. Competition and Parasitism Malware may remove competing malware. May exploit backdoors/RCI left by previous malware. May infect competing malware, hijacking its propagation. CSC 482/582: Computer Security

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. CSC 482/582: Computer Security

Detecting Malware Signature-based Smart scanning Decryption 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 482/582: Computer Security

Detecting Malware Code Emulation Code Optimization. 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 482/582: Computer Security

Detecting Malware Heuristics Neural Network 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 482/582: Computer Security

Detecting Malware Behavior-based Integrity Checking 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, Osiris CSC 482/582: Computer Security

Defences: 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. CSC 482/582: Computer Security

Defences: 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? CSC 482/582: Computer Security

Defences: 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. CSC 482/582: Computer Security

Defences: 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. CSC 482/582: Computer Security

Defences: 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. CSC 482/582: Computer Security

Defences: 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. http://www.securityfocus.com/news/7517 http://xforce.iss.net/xforce/alerts/id/150 CSC 482/582: Computer Security

Fast Worms Slammer Worm Characteristics 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. Shutdown 13,000 Bank of America ATMs due to compromising db servers, heavy traffic. http://www.securityfocus.com/news/7517 CSC 482/582: Computer Security

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.) CSC 482/582: Computer Security

Profitable Malware Trojans Spyware and Adware 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. CSC 482/582: Computer Security

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. Around a 1000 pieces of mobile malware exist. For Blackberries and Palm Pilots too. Expect more as smart phones become common. MMS=multimedia messaging system CSC 482/582: Computer Security

Offline Impact Davis-Besse nuclear power plant Seattle 911 system 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. CSC 482/582: Computer Security

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. CSC 482/582: Computer Security

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. CSC 482/582: Computer Security