Lecture 15 Overview

Kinds of Malicious Codes

• Virus: a program that attaches copies of itself into other programs. – Propagates and performs some

unwanted function– Viruses are not programs– Definition from RFC 1135: A virus is a piece of code

that inserts itself into a host [program], including operating systems, to propagate. It cannot run independently. It requires that its host program be run to activate it.

2CS 450/650 Lecture 15: Malicious Codes

Kinds of Malicious Code• Worm: a program that propagates copies of

itself through the network. – Independent program. – May carry other code, including

programs and viruses. – Definition from RFC 1135: A worm is a program that

can run independently, will consume the resources of its host [machine] from within in order to maintain itself and can propagate a complete working version of itself on to other machines.

3CS 450/650 Lecture 15: Malicious Codes

Kinds of Malicious Code

• Rabbit/Bacteria: make copies of themselves to overwhelm a computer system's resources– Denying the user access to the resources

• Logic/Time Bomb: programmed threats that lie dormant for an extended period of time until they are triggered– When triggered, malicious code is executed

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Kinds of Malicious Code• Trojan Horse: secret, undocumented routine

embedded within a useful program – Execution of the program results in execution of

secret code• Trapdoor: secret, undocumented entry point

into a program, used to grant access without normal methods of access authentication

• Dropper: Not a virus or infected file– When executed, it installs a virus into memory, on

to the disk, or into a file5CS 450/650 Lecture 15: Malicious Codes

Virus Lifecycle

• Dormant phase: the virus is idle– not all viruses have this stage

• Propagation phase: the virus places an identical copy of itself into other programs of into certain system areas

• Triggering phase: the virus is activated to perform the function for which it was created

• Execution phase: the function is performed– The function may be harmless or damaging

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Virus Types

• Parasitic virus: – Attaches itself to a file and replicates when the

infected program is executed– most common form

• Memory resident virus: – lodged in main memory as part of a resident

system program– Virus may infect every program that executes

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Virus Types

• Boot Sector Viruses:– Infects the boot record and spreads when system

is booted– Gains control of machine before the virus

detection tools– Very hard to notice

• Macro Virus:– virus is part of the macro associated with a

document8CS 450/650 Lecture 15: Malicious Codes

Virus Types

• Stealth virus: – A form of virus explicitly designed to hide from

detection by antivirus software

• Polymorphic virus: – A virus that mutates with every infection making

detection by the “signature” of the virus difficult

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How Viruses Append

10

Original

program

virus

Original

program

virus

Virus appended to program

+ =

CS 450/650 Lecture 15: Malicious Codes

Original

program

Virus-1

Virus-2

Virus surrounding a program

Original

program

Virus-1

Virus-2

Virus-3Virus-4

Virus integrated into program

How Viruses Gain Control

• Virus V has to be invoked instead of target T– V overwrites T– V changes pointers from T to V

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Virus Signatures

• Storage pattern– Code always located on a specific address– Increased file size

• Execution pattern

• Transmission pattern

• Polymorphic Viruses

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Antivirus Approaches

• Detection: – determine infection and locate the virus

• Identification: – identify the specific virus

• Removal: – remove the virus from all infected systems, so the

disease cannot spread further

• Recovery: – restore the system to its original state

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Preventing Virus Infection

• Prevention:– Good source of software installed – Isolated testing phase– Use virus detectors

• Limit damage:– Make bootable diskette– Make and retain backup copies important

resources

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Worm• Self-replicating (like virus)• Objective: system penetration (intruder)• Phases: dormant, propagation, triggering, and

execution • Propagation:– Searches for other systems to infect

• e.g., host tables

– Establishes connection with remote system– Copies itself to remote system– Execute

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Lecture 16

Targeted Malware

CS 450/650

Fundamentals of Integrated Computer Security

Slides are modified from Csilla Farkas and Brandon Phillips

Targeted Malicious Code

• Trapdoor– undocumented entry point to a module

– forget to remove them– intentionally leave them in the program for testing– intentionally leave them in the program for

maintenance of the finished program, or– intentionally leave them in the program as a

covert means of access to the component after it becomes an accepted part of a production system

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Targeted Malicious Code

• Salami Attack– a series of many minor actions that together

results in a larger action that would be difficult or illegal to perform at once

– Ex. Interest computation

• rootkit – A program or coordinated set of programs

designed to gain control over a computer system or network of computing systems

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Targeted Malicious Code

• Privilege Escalation– a means for malicious code to be launched by a

user with lower privileges but run with higher privileges

• Interface illusion – a spoofing attack in which all or part of a web

page is false

• Keystroke Logging

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Targeted Malicious Code

• Man-in-the-Middle Attacks

• Timing Attacks– attempts to compromise a cryptosystem by

analyzing the time taken to execute cryptographic algorithms

• Covert Channels– programs that leak information– Ex. Hide data in output

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Covert Channel - Trojan Horse

John

Spy

Only John

is permitted

to access

the document

MS Word

Document

Spy’s

Document

copy

TH

installcopy

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Covert Channel• Two active agents

– Sender (has access to unauthorized information)• e.g., Trojan Horse in MS Word

– Receiver (reads sent information)• e.g., program creating the copy

• Encoding schema– How the information is sent

• e.g., – File F exists 0– File F is does not exist 1

• Synchronization– e.g., when to check for existence of F

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Storage Covert Channels

• Based on properties of resources– pass information by using presence or absence of

objects in storage

• Examples:– File locks– Delete/create file– Memory allocation

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File Lock Covert Channel

24

File Existence Channel Used to Signal 100

25

Timing Covert Channel

• Time is the factor – how fast– pass information using the speed at which things

happen

• Examples:– Processing time– Transmission time

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Covert Timing Channel

27

Covert Channel Detection and Removal

• Identification:– Shared resources– Program code correctness– Information flow analysis

• Removal:– Total removal – may not be possible– Reduce bandwidth

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Controls Against Program Threats

• Prevent Threats during software development– Modularity• security analysts must be able to understand each

component as an independent unit and be assured of its limited effect on other components

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Controls Against Program Threats

• Prevent Threats during software development– Encapsulation• hide a component's implementation details • minimize interfaces to reduce covert channels

– Information hiding • a component as a kind of black box • components will have limited effect on other

components

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Controls Against Program Threats

• Peer Reviews– Hazard Analysis• set of systematic techniques to expose potentially

hazardous system states

– Testing • unit testing, integration testing, function testing,

performance testing, acceptance testing, installation testing, regression testing

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Controls Against Program Threats

• Good Design– Using a philosophy of fault tolerance– Have a consistent policy for handling failures– Capture the design rationale and history– Use design patterns

• Prediction– predict the risks involved in building and using the

system

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Controls Against Program Threats

• Static Analysis– Use tools and techniques to examine characteristics

of design and code to see if the characteristics warn of possible faults

• Configuration Management– control changes during development and

maintenance• Analysis of Mistakes• Proofs of Program Correctness– Can we prove that there are no security holes?

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Operating System Controls on Use of Programs

• Trusted Software– code has been rigorously developed and analyzed• Functional correctness• Enforcement of integrity• Limited privilege• Appropriate confidence level

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Operating System Controls on Use of Programs

• Mutual Suspicion– assume other program is not trustworthy

• Confinement – limit resources that program can access

• Access Log – list who access computer objects, when, and for

how long

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Administrative Controls

• Standards of Program Development• Standards of design• Standards of documentation, language, and coding

style• Standards of programming• Standards of testing• Standards of configuration management• Security Audits

• Separation of Duties

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