Operating Systems: Internals and Design Principles, 6/E William Stallings - Chapter 14: Computer Security Threats

Computer Security Concepts

Threats, Attacks, and Assets

Intruders

Malicious Software Overview

Viruses, Worms, and Bots

Rootkits

 

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Chapter 14 Computer Security ThreatsDave BremerOtago Polytechnic, N.Z. ©2008, Prentice HallOperating Systems: Internals and Design Principles, 6/E William StallingsRoadmapComputer Security ConceptsThreats, Attacks, and AssetsIntrudersMalicious Software OverviewViruses, Worms, and BotsRootkitsSecurity definitionThe NIST Computer Security Handbook defines computer security as:The protection afforded to an automated information system in order to attain the applicable objectives of preserving the integrity, availability and confidentiality of information system resourcesComputer Security TriadThree key objectives are at the heart of computer securityConfidentialityIntegrityAvailabilityAdditional ConceptsTwo further concepts are often added to the core of computer securityAuthenticityAccountabilityRoadmapComputer Security ConceptsThreats, Attacks, and AssetsIntrudersMalicious Software OverviewViruses, Worms, and BotsRootkitsThreatsRFC 2828, describes four kinds of threat consequences Unauthorised DisclosureDeceptionDisruptionUsurptionAttacks resulting in Unauthorised DisclosureUnauthorised Disclosure is a threat to confidentiality. Attacks include:Exposure (deliberate or through error) InterceptionInferenceIntrusion Attacks resulting in DeceptionDeception is a threat to either system integrity or data integrity.Attacks include:MasqueradeFalsificationRepudiationAttacks resulting in DisruptionDisruption is a threat to availability or system integrity.Attacks include:IncapacitationCorruptionObstruction Attacks resulting in usurpationUsurpation is a threat to system integrity. Attacks include:MisappropriationMisuseAssetsThe assets of a computer system can be categorized as hardware, software, data, communication lines and networks.Scope of System SecurityAssets in Relation to the CIA TriadRoadmapComputer Security ConceptsThreats, Attacks, and AssetsIntrudersMalicious Software OverviewViruses, Worms, and BotsRootkitsIntrudersThree main classes of intruders:Masquerader, Typically an outsiderMisfeasorOften an insider and legitimate userClandestine userIntruder Behavior: HackersIntruder Behavior: Criminal EnterpriseIntruder Behavior: Internal ThreatRoadmapComputer Security ConceptsThreats, Attacks, and AssetsIntrudersMalicious Software OverviewViruses, Worms, and BotsRootkitsMalwareGeneral term for any Malicious softWareSoftware designed to cause damage Or use up the resources of a target computer. Some malware is parasiticContained within other softwareSome malware is self-replicating, others require some other means to propogate.BackdoorTrapdoorSecret entry pointUseful for programmers debuggingBut allows unscrupulous programmers to gain unauthorized access.Logic BombExplodes when certain conditions are metPresence or absence of certain filesParticular day of the weekParticular user running applicationTrojan HorseUseful program that contains hidden code that when invoked performs some unwanted or harmful functionCan be used to accomplish functions indirectly that an unauthorized user could not accomplish directlyUser may set file permission so everyone has accessMobile CodeTransmitted from remote system to local systemExecuted on local system without the user’s explicit instructionCommon example is cross-site scripting attacksMultiple-Threat MalwareMultipartite virus infects in multiple waysBlended attack uses multiple methodsEx: Nimda has worm, virus, and mobile code characteristicsRoadmapComputer Security ConceptsThreats, Attacks, and AssetsIntrudersMalicious Software OverviewViruses, Worms, and BotsRootkitsParts of VirusSoftware that “infects” other software by modifying themModification includes An infection mechanismTriggerPayloadVirus StagesDuring its lifetime, a typical virus goes through the following four phases:Dormant phasePropagation phaseTriggering phaseExecution phase29Virus StructureMay be prepended, postpended, or embedded in an executableWhen the executable runs, it first executes the virus, then calls the original code of the programSimple VirusCompression VirusVirus ClassificationThere is no simple or universally agreed upon classification scheme for viruses, It is possible to classify a virus by a number of means includingBy targetBy Concealment strategyby TargetBoot sector infectorFile infectorMacro virusby Concealment StrategyEncrypted virusRandom encryption key encrypts remainder of virusStealth virusHides itself from detection of antivirus softwarePolymorphic virusMutates with every infectionMetamorphic virusMutates with every infectionRewrites itself completely after every iterationMacro VirusesPlatform independentMost infect Microsoft Word documentsInfect documents, not executable portions of codeEasily spreadFile system access controls are of limited use in preventing spread36E-Mail VirusesMay make use of MS Word macro’sIf someone opens the attachment itAccesses the local address book and sends copies of itself to contactsMay perform local damageWormsReplicates itselfUse network connections to spread form system to systemEmail virus has elements of being a worm (self replicating)But normally requires some intervention to run, so classed as a virus rather than worm38Worm PropogationElectronic mail facilityA worm mails a copy of itself to other systemsRemote execution capabilityA worm executes a copy of itself on another systemRemote log-in capabilityA worm logs on to a remote system as a user and then uses commands to copy itself from one system to the otherWorm Propagation ModelBotsFrom RobotAlso called Zombie or droneProgram secretly takes of another Internet-attached computerLaunch attacks that are difficult to trace to bot’s creatorCollection of bots is a botnetRoadmapComputer Security ConceptsThreats, Attacks, and AssetsIntrudersMalicious Software OverviewViruses, Worms, and BotsRootkitsRootkitSet of programs installed on a system to maintain administrator (or root) access to that systemHides its existenceAttacker has complete control of the system.Rootkit classificationRootkits can be classified based on whether they can survive a reboot and execution mode.PersistentMemory basedUser modeKernel modeRootkit installationOften as a trojanCommonly attached to pirated softwareInstalled manually after a hacker has gained root accessSystem Call Table Modification by RootkitPrograms operating at the user level interact with the kernel through system calls.Thus, system calls are a primary target of kernel-level rootkits to achieve concealment.Changing SyscallsThree techniques that can be used to change system calls: Modify the system call table Modify system call table targetsRedirect the system call tableKnark rootkit modifying syscall table

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