Viruses and Related Threats

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Summary have considered:

various malicious programs trapdoor, logic bomb, trojan horse, zombie viruses worms countermeasures distributed denial of service attacks

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Viruses and Related Threats Viruses

Computer viruses have got a lot of publicity One of a family of malicious software

Malicious software is software that is intentionally included or inserted in a system for a harmful purpose

Effects usually obvious They have figured in news reports, fiction, movies

often exaggerated getting more attention than deserve

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Viruses and Related Threats Malicious Programs

Dependent program They Need host programs They cannot exist independent of some actual application E.g.: Viruses, Logic bomb, Backdoor

Independent program They can be scheduled and run by the OS E.g.: Worm, Zombie

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Viruses and Related Threats

Taxonomy of Malicious Programs

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Viruses and Related Threats Backdoor or Trapdoor

A secret entry point in a program It allows those who know access bypassing usual security

procedures It have been commonly used by developers A threat when left in production programs allowing

exploited by attackers It is very hard to block in O/S It requires good s/w development & update

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Viruses and Related Threats Logic Bomb

One of oldest types of malicious software Code embedded in legitimate program It is activated when specified conditions met

Example presence/absence of some file particular date/time particular user

When triggered typically damage system E.g., modify/delete files/disks, halt machine, etc

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Viruses and Related Threats Trojan Horse

A program (or some part of a program) with hiddenside-effects

Trojan horse is usually attractive to run E.g., freeware game, s/w upgrade, etc

when runs, it performs some additional tasks allows attacker to indirectly gain access they do not have directly

E.g., destroy/modify data, …

It often used to propagate a virus/worm or install a backdoor

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Viruses and Related Threats Zombie

A program which secretly takes over another networkedcomputer

Then, the attacker uses the zombies to indirectly launchattacks (to the target host) => Zombies often used to launch distributed denial of service

(DDoS) attacks

Zombie exploits known flaws in network systems

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Viruses and Related Threats The Nature of Viruses

Viruses: a piece of self-replicating code attached to someother code Cf. biological virus

Both (biological/computer virus) carry a payload and propagate itself Payload contains code to make copies of itself as well as code to

perform some covert task

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Viruses and Related Threats Virus phases:

Dormant – waiting on trigger event Propagation – replicating to programs/disks Triggering – activated by event to execute payload Execution – performing the functions in the payload

Detailed phases usually depend on machine/OS specific exploiting features/weaknesses

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Viruses and Related Threats

program V :={go to main :

1234567; subroutine infect-executable :=

{loop:file:=get-random-executable-file;if( first-line-of-file = 1234567 ) then goto loop else prepend V to file;}subroutine do-damage := {whatever damage is to be done}subroutine trigger-pulled := {return true if some condition holds}

main : main-program :={infect-executable;if trigger-pulled then do-damage;goto next;}

next;}

- A simple virus- This virus is easily detectedbecause an infected version of aprogram is longer than thecorresponding uninfected one

• Virus Structure

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Viruses and Related Threats

program CV :={go to main :

01234567; subroutine infect-executable := {loop:

file:=get-random-executable-file;if( first-line-of-file = 1234567 ) then goto loop(1) compress file;(2) prepend CV to file; }

main : main-program :={infect-executable;(3) uncompress rest-of-file;(4) run uncompressed file;goto next;}

next;}

- A Compression virus :A way to thwart a means ofdetecting a simple virus is tocompress the executable file so thatboth the infected and uninfectedversions are of identical length.

• Logic of Compression Virus

Running steps of compressed P1’ filethat contains the virus code.

1. For each uninfected file P2,the virus first compress P2 toproduce P2’.

2. The virus code is prepended to theP2’

3. P1’ is uncompressed to P14. P1 is executed

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Viruses and Related Threats

A Compression Virus

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Viruses and Related Threats Types of Viruses

We can classify on basis of how they attack Parasitic virus

it attaches itself to executable files and replicates. Memory-resident virus

Lodges in main memory as part of a resident system program. Boot sector virus

Infects a master boot record or boot record. Stealth virus

A form of virus explicitly designed to hide itself from detection by antivirus software.

Polymorphic virus A virus that mutates with every infection.

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Viruses and Related Threats Macro Virus

macro code can be attached to some data file which is interpreted by program using file E.g., Word/Excel macros Esp. using auto command & command macros

Macro code is now platform independent Macro virus is a major source of new viral infections There is blur distinction between data and program files Classic trade-off: "ease of use" vs "security” Successive release of Word provide increased protection,

and today macro virus is no longer dominant virus threat

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Viruses and Related Threats Email Virus

Email viruses are spread using email with attachmentcontaining a macro virus cf Melissa

They are triggered when user opens attachment, or worseeven when mail viewed by using scripting features in mailagent => hence propagate very quickly

Usually targeted at Microsoft Outlook mail agent & Word/Excel documents

We need better O/S & application security

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Viruses and Related Threats Worms

Originally, worms are self-replicating programs but not infecting ones.

Typically, spread over a network E.g., Morris Internet Worm in 1988, which led to creation of CER

Ts Worms propagate by using users’ distributed privileges or

by exploiting system vulnerabilities Recently, worms are widely used by hackers to create zo

mbie PC's, subsequently used for further attacks, esp. DoS (Denial-of-Services) attack.

Major issue is lack of security of permanently connected systems, esp. PC's

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Viruses and Related Threats It exhibits the same characteristics as a computer virus The propagation phase performs the following functions :

Search for other systems to infect by examining host tables Establish a connection with a remote system. Copy itself to the remote system and cause the copy to be run.

It may also disguise its presence by naming itself as a system process or using some other name that may not be noticed by a system operator.

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Viruses and Related Threats Morris Worm

best known classic worm released by Robert Morris in 1988 targeted Unix systems using several propagation techniques

simple password cracking of local pw file exploit bug in finger daemon exploit debug trapdoor in sendmail daemon

if any attack succeeds then replicated self

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Viruses and Related Threats Recent Worm

Attacks new spate of attacks from mid-2001 Code Red - used MS IIS bug

probes random IPs for systems running IIS had trigger time for denial-of-service attack 2nd wave infected 360000 servers in 14 hours

Code Red 2 - installed backdoor Nimda - multiple infection mechanisms SQL Slammer - attacked MS SQL server Sobig.f - attacked open proxy servers Mydoom - mass email worm + backdoor

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Viruses and Related Threats State of Worm Technology

multiplatform multiexploit ultrafast spreading polymorphic metamorphic transport vehicles zero-day exploit

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Virus Countermeasures Best countermeasure is prevention However, in general not possible Hence, we need to do one or more of:

Detection - of viruses in infected system Identification - of specific infecting virus Removal - restoring system to clean state

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Virus Countermeasures Anti-Virus Approaches

first-generation scanner uses virus signature to identify virus or change in length of programs

second-generation uses heuristic rules to spot viral infection or uses crypto hash of program to spot changes

third-generation memory-resident programs identify virus by actions

fourth-generation packages with a variety of antivirus techniques eg scanning & activity traps, access-controls

arms race continues

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Virus Countermeasures Advanced Anti-Virus Techniques

Generic decryption It use CPU simulator to check program signature & behavior befo

re actually running it It start the simulator to simulate the file execution Note that all polymorphic virus should decrypt itself to activate. By periodically scanning the memory, decrypted virus code can be detected.

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Virus Countermeasures Digital Immune System

It is a comprehensive approach to virus protection developed by IBM

The objective of this system is to provide rapid response time so that viruses can be stamped out almost as soon as they are introduced

It uses general purpose emulation & virus detection Any virus entering org is captured, analyzed, detection/shielding c

reated for it, removed

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Virus Countermeasures

Digital Immune SystemDigital Immune System

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Virus Countermeasures Behavior-Blocking Software

integrated with host O/S monitors program behavior in real-time

E.g., file access, disk format, executable modifications, system settings changes, network access

For possibly malicious actions, if detected can block, terminate, or seek OK

B-B s/w has advantage over scanners But, malicious code runs before detection

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Distributed Denial of Service Attacks(DDoS)

Denial of Service (DoS) attacks An attempt to make a computer resource unavailable to its intended u

sers. Typically, the targets are high-profile web servers where the attack is

aiming to cause the hosted web pages to be unavailable on the Internet.

Distributed Denial of Service (DDoS) attacks Attacks form a significant security threat where it makes networked

systems unavailable by flooding with useless traffic It uses large numbers of “zombies” It is one of growing sophistication of attacks Defense technologies are struggling to cope

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Distributed Denial of Service Attacks(DDoS)

Distributed Denial of Service Attacks (Distributed Denial of Service Attacks (DDoSDDoS))

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Distributed Denial of Service Attacks(DDoS)

Constructing the DDoS Attack Network We must infect large number of zombies Requirements.:1. Software to implement the DDoS attack2. An unpatched vulnerability on many systems3. A scanning strategy to find vulnerable systems

random, hit-list, topological, local subnet

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Distributed Denial of Service Attacks(DDoS)

DDoS Countermeasures Three broad lines of defense:

1. Attack prevention & preemption (before)2. Attack detection & filtering (during)3. Attack source traceback & identification (after)

There are huge range of attack possibilities Hence, DDos contermeasures must evolve with the threat