lecture 12. web application security

8/8/2019 Lecture 12. Web Application Security

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Web Application SecurityWeb Application SecurityInternet technologyInternet technology -- IT00803IT00803


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OverviewOverview

What is Security?What is Security?

5 (+ or5 (+ or -- 2) Aspects of Security2) Aspects of Security

Fundamental TechnologiesFundamental Technologies Secure Client/Server InteractionSecure Client/Server Interaction

Securing the ClientSecuring the Client

Securing the ServerSecuring the Server

Securing Web ApplicationsSecuring Web Applications


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What is Security?What is Security?

The definition of security, as it applies, to theThe definition of security, as it applies, to the

Web, is often too narrow.Web, is often too narrow.

An SSLAn SSL--enabled Web application?enabled Web application?

A properly patched and firewalled server?A properly patched and firewalled server?

Service availabilityService availability

Managing riskManaging risk

Traditional risk analysisTraditional risk analysis Best practicesBest practices

Compliance with legal obligationsCompliance with legal obligations

CopyrightsCopyrights

Privacy lawsPrivacy laws


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5 (5 ( 2 ) Aspects of Security2 ) Aspects of Security

Confidentiality

Integrity Availability


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Availability

Non-Repudiation Authorization

Confidentiality

Integrity

Authentication


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Non-Repudiation Authorization

Confidentiality

Integrity

Authentication

Privacy

Availability


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ConfidentialityConfidentiality

Information exchanged between theInformation exchanged between theclient and service provider cannot beclient and service provider cannot beread by an unauthorized party.read by an unauthorized party.

Encryption is the fundamentalEncryption is the fundamentaltechnology for ensuring confidentialitytechnology for ensuring confidentiality

Messages in transitMessages in transit

Messages in storageMessages in storage Confidentiality vs. PrivacyConfidentiality vs. Privacy

Confidentiality: Obligation ofConfidentiality: Obligation ofproviderprovidertotorestrict access.restrict access.

Privacy:Privacy: individualindividualright to control access.right to control access.


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IntegrityIntegrity

The assurance that data & information cannot beThe assurance that data & information cannot be

altered.altered.

Accidental corruptionAccidental corruption

Willful alterationWillful alteration Here, we discuss integrity in terms ofHere, we discuss integrity in terms ofdata integritydata integrity

Data has not been altered during transmissionData has not been altered during transmission

In CIA model,In CIA model, source integritysource integrity= authentication= authentication

Primary technologies/techniques to ensure integrity:Primary technologies/techniques to ensure integrity:

Digital signaturesDigital signatures

Hash algorithmsHash algorithms

ChecksumsChecksums


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AvailabilityAvailability

Authorized clients have timely andAuthorized clients have timely and

reliable access to resources.reliable access to resources.

Proper availability depends onProper availability depends onapplicationapplication

Myth of the NinesMyth of the Nines

How reliable is 99.9% availability?How reliable is 99.9% availability?

Relevant technologies/techniquesRelevant technologies/techniques

High availability protocolsHigh availability protocols

RedundancyRedundancy

S stem desi n without sin le oint of failureS stem desi n without sin le oint of failure


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AuthenticationAuthentication

Is the client (person or machine) reallyIs the client (person or machine) reallywho they claim to be?who they claim to be?

The most secure authentication schemesThe most secure authentication schemesuse 3 factors:use 3 factors:

Something youSomething you knowknow e.g., passworde.g., password

Something youSomething you havehave e.g., key/tokene.g., key/token

Something youSomething you areare e.g., fingerprinte.g., fingerprint

TechnologiesTechnologies

Login/password combinationLogin/password combination

Public Key InfrastructurePublic Key Infrastructure

BiometricsBiometrics


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AuthorizationAuthorization

Allowing access only to those resourcesAllowing access only to those resourcesto which the client has been grantedto which the client has been grantedpermission.permission.

Granting authorization may depend on:Granting authorization may depend on:

IdentityIdentity

Client characteristic (e.g., age, domain)Client characteristic (e.g., age, domain)

Access control list (ACL) is still theAccess control list (ACL) is still theprimary technology.primary technology.

So, whats the difference betweenSo, whats the difference betweenauthenticationauthentication && authorization?authorization?


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NonNon--Repudiation (Auditing)Repudiation (Auditing)

Preventing both the sender & receiver ofPreventing both the sender & receiver of

information from denying theirinformation from denying their

involvement in an exchange.involvement in an exchange.

SenderSenderreceives proof ofreceives proof ofdeliverydelivery..

RecipientRecipient receives proof ofreceives proof oforiginorigin..

NonNon--repudiation encompasses:repudiation encompasses:

Approval & sending (origin)Approval & sending (origin)

SubmissionSubmission

TransportTransport

Receipt & Knowledge (delivery)Receipt & Knowledge (delivery)


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PrivacyPrivacy

The clients expectation that their dataThe clients expectation that their datawill be released only to those parties thatwill be released only to those parties thattheytheyauthorize.authorize.

Common view of privacy invasionsCommon view of privacy invasions CookiesCookies

SpywareSpyware

Privacy expectations vary acrossPrivacy expectations vary acrosssocieties and industries.societies and industries.

HighHigh: Europe, health care (HIPAA Privacy: Europe, health care (HIPAA PrivacyRule)Rule)

LowLow: North America in general: North America in general


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FundamentalFundamental

TechnologiesTechnologies


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Introduction to EncryptionIntroduction to Encryption

A mathematical process for transforming a plain textA mathematical process for transforming a plain textmessage intomessage into cipher text.cipher text.

AA ciphercipheris an algorithm for encrypting or decrypting ais an algorithm for encrypting or decrypting amessage.message.

lassical ciphersClassical ciphers substitution & transpositionsubstitution & transposition

Modern ciphersModern ciphers mathematical transformationsmathematical transformations

Symmetric vs. asymmetricSymmetric vs. asymmetric

Block vs. streamBlock vs. stream

A cipher is said to be strong if it cannot be broken by aA cipher is said to be strong if it cannot be broken by abrutebrute--force attackforce attack(i.e., trying all possible keys)(i.e., trying all possible keys)


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Symmetric Key AlgorithmsSymmetric Key Algorithms

The sender/receiver use the same key toThe sender/receiver use the same key toencrypt/decrypt a message.encrypt/decrypt a message.

ExamplesExamples: AES, Blowfish, DES, Triple: AES, Blowfish, DES, Triple--DESDES

Not all algorithms are created alike.Not all algorithms are created alike. Secrecy of the keySecrecy of the key

Key lengthKey length

Inversion of the encryption algorithmInversion of the encryption algorithm

Known parts of the plaintext.Known parts of the plaintext.

BiggestBiggest advantageadvantage: speed: speed

BiggestBiggest disadvantagesdisadvantages: key exchange, storage: key exchange, storage


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How DES WorksHow DES Works

5656--bit key length (64bit key length (64 8 parity bits)8 parity bits)

Actual # of keys (humanActual # of keys (human--entered) = 96entered) = 9688

No longer considered a strong algorithm.No longer considered a strong algorithm.

TripleTriple--DES produces effective length of 168 bitsDES produces effective length of 168 bits

Source: Web Engineering, Kappel et. al.


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Public Key AlgorithmsPublic Key Algorithms

Sender and receiver employ different keysSender and receiver employ different keys

for encrypting/decrypting a message.for encrypting/decrypting a message.

Each person/entity has a publicEach person/entity has a public--priv

ate keypriv

ate keypairpair

Private key mustPrivate key must neverneverbe revealed!be revealed!

ExamplesExamples

DiffieDiffie--HellmanHellman originally proposed in 1975.originally proposed in 1975.

RSARSA

Most commonly used for encryption andMost commonly used for encryption and

digitalsignaturesdigitalsignatures..


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How Public Key AlgorithmsHow Public Key Algorithms

WorkWork

Source: Web Security, Privacy & Commerce. Garfinkel.


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Digital SignaturesDigital Signatures

Rely on public key algorithms andRely on public key algorithms and hashhashfunctionsfunctions to provide:to provide:

IntegrityIntegrity

NonNon--repudiationrepudiationAuthenticationAuthentication

A hash function (e.g., MD5, SHAA hash function (e.g., MD5, SHA--1) creates a1) creates asmallsmall message digestmessage digest, or fingerprint, of the, or fingerprint, of the

much larger original message.much larger original message. By signing the digest with a private key, itBy signing the digest with a private key, it

becomes virtually impossible to alter a messagebecomes virtually impossible to alter a messagewithout detection.without detection.


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Digital Certificates & PKIDigital Certificates & PKI

In reality, public key encryption is viableIn reality, public key encryption is viableprovided we can trust the integrity of theprovided we can trust the integrity of thepublic key itself.public key itself.

Public Key Infrastructures provide thisPublic Key Infrastructures provide thisintegrity throughintegrity through delegated trustdelegated trust..

X.509 Digital CertificatesX.509 Digital Certificates binds public keys tobinds public keys toidentity of the private key holderidentity of the private key holder

PGP and GPGPGP and GPG A Certification Authority (CA) digitally signsA Certification Authority (CA) digitally signs

issued certificates to vouch for the integrityissued certificates to vouch for the integrityof the certificate.of the certificate.


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The Limits of CryptographyThe Limits of Cryptography

Encryption is but one of the tools necessaryEncryption is but one of the tools necessary

for Web security.for Web security.

Encryption alone doesnt solve all securityEncryption alone doesnt solve all security

problems.problems.

Unencrypted documentsUnencrypted documents

Stolen keysStolen keys

DenialDenial--ofof--service attacksservice attacks Traffic analysisTraffic analysis

Compromised encryption programsCompromised encryption programs

Human errorsHuman errors


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Secure Client/ServerSecure Client/Server

InteractionInteraction


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Secure vs. NonSecure vs. Non--secure Appssecure Apps

So, why arent the secure apps adopted?So, why arent the secure apps adopted? Security vs. convenience.Security vs. convenience.

Average user is unaware of them.Average user is unaware of them.

Costs outweigh benefits.Costs outweigh benefits.

PurposePurpose NonNon--securesecure SecureSecure

WebbrowsingWebbrowsing HTTPHTTP HTTPS (SSL)HTTPS (SSL)

File TransferFile Transfer FTPFTP SFTP, SCPSFTP, SCP

RemoteRemote

Access (UNIX)Access (UNIX)

TelnetTelnet SSHSSH


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Secure Sockets Layer (SSL)Secure Sockets Layer (SSL)

Originally released by Netscape (1996), allowing for:Originally released by Netscape (1996), allowing for:

Authentication of the server & client (dig. sig.)Authentication of the server & client (dig. sig.)

Confidentiality (encryption)Confidentiality (encryption)

Integrity (message authentication codes)Integrity (message authentication codes) SSLs features have made it popularSSLs features have made it popular

Separation of dutiesSeparation of duties

EfficiencyEfficiency

CertificateCertificate--based authenticationbased authentication

Protocol agnostic (doesnt require TCP/IP)Protocol agnostic (doesnt require TCP/IP)

Protection against certain attacksProtection against certain attacks


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SSL Handshake, Step by StepSSL Handshake, Step by Step

1.1. Client sends HTTPS request, includingClient sends HTTPS request, includinginfo about its cryptographic settings.info about its cryptographic settings.

2.2. Server replies with its encryptionServer replies with its encryptionsettings and its certificate.settings and its certificate.

3.3. Client verifies validity of certificate.Client verifies validity of certificate. Is issuing CA trusted?Is issuing CA trusted?

Verify signature with CAs public key.Verify signature with CAs public key.

Verify validity period.Verify validity period.

Verify domain name.Verify domain name.

Verify certificate is not on revocation list.Verify certificate is not on revocation list.


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SSL Handshake, Step by StepSSL Handshake, Step by Step --22

4.4. Client generates a preClient generates a pre--master secret,master secret,encrypts it using servers public key, andencrypts it using servers public key, and

sends to server.sends to server.

5.5. Client & server generate a master secretClient & server generate a master secretbased on the prebased on the pre--master secret.master secret.

6.6. Using master secret, both client & serverUsing master secret, both client & servergenerate agenerate a symmetric keysymmetric keyfor thefor the sessionsession..

7.7. Client informs server that future messagesClient informs server that future messageswill be encrypted; sends encryptedwill be encrypted; sends encrypted

messages acknowledging completion.messages acknowledging completion.

8.8. Server does the same.Server does the same.


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Authentication MethodsAuthentication Methods

Were all familiar with login/password.Were all familiar with login/password.

Best practice: use SSLBest practice: use SSL--secured connections.secured connections.

Also wise to store hashed or encrypted passwordsAlso wise to store hashed or encrypted passwordson server.on server.

Digital CertificatesDigital Certificates

Can be used for email or web browsing.Can be used for email or web browsing.

Average user does not possess one.Average user does not possess one.

SingleSingle--sign onsign on

Example systems: Kerberos, Microsoft PassportExample systems: Kerberos, Microsoft Passport

Upon initial signUpon initial sign--on, clients receive a token.on, clients receive a token.

Can be used across an organization or enterprise.Can be used across an organization or enterprise.


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Authorization & Access ControlsAuthorization & Access Controls

Authorization policies specify what resourcesAuthorization policies specify what resourcesauthenticated users may access.authenticated users may access.

For files,For files, access control listsaccess control lists (ACL) are the most(ACL) are the mostpopular mechanism.popular mechanism.

Explicitly ALLOW orDENY accessExplicitly ALLOW orDENY access

OS or Web server level (e.g., .htaccess files inOS or Web server level (e.g., .htaccess files inApache)Apache)

Individual, group, role, or everyone.Individual, group, role, or everyone.

Domain, user characteristics, time of day, etc.Domain, user characteristics, time of day, etc. For greater security, evaluation points (page, gateway)For greater security, evaluation points (page, gateway)

are separated from the decision point. (application)are separated from the decision point. (application)


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Securing the ClientSecuring the Client


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OverviewOverview

What you can control, as a serviceWhat you can control, as a serviceprovider:provider:

SSLSSL--enabled connectionsenabled connections

Preserving PrivacyPreserving Privacy

Sandboxes & Code signingSandboxes & Code signing

What you cant controlWhat you cant control

Desktop securityDesktop securityAntiAnti--virus applicationsvirus applications

FirewallsFirewalls

Intrusion detectionIntrusion detection

Phishing and web spoofingPhishing and web spoofing


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Preserving PrivacyPreserving Privacy

Platform for Privacy Preferences (P3P)Platform for Privacy Preferences (P3P)

W3C standard for privacy policies (2002).W3C standard for privacy policies (2002).

Supported by major browsers.Supported by major browsers.

An XMLAn XML--based standard for publishing privacybased standard for publishing privacypolicies.policies.

Allows privacy agents (e.g., Privacy Bird) toAllows privacy agents (e.g., Privacy Bird) to

evaluate a websites privacy policy for you.evaluate a websites privacy policy for you.

Relies on goodRelies on good--faith of websites.faith of websites.

MotivationMotivation

Help users gain more control over disclosure ofHelp users gain more control over disclosure of

personal information.personal information.

Help organizations gain customers trust.Help organizations gain customers trust.


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Sandboxing & Code SigningSandboxing & Code Signing

SandboxSandbox: restricted environment for: restricted environment fordownloaded code (e.g., a Java applet).downloaded code (e.g., a Java applet).

E.g., Cannot access file system.E.g., Cannot access file system.

Restricts both malicious and trusted.Restricts both malicious and trusted.

If more functionality is requiredIf more functionality is required

User adjust security policy (highly unlikely)User adjust security policy (highly unlikely)

Service provider digitally signs code.Service provider digitally signs code. Both Java and ActiveX rely on codeBoth Java and ActiveX rely on code

signing.signing.

Signed code isSigned code ispotentiallypotentiallytrusted code.trusted code.

Unsigned or untrusted code is rejected.Unsigned or untrusted code is rejected.


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Securing the DesktopSecuring the Desktop

Threats enter the system at the mostThreats enter the system at the mostvulnerable points.vulnerable points.

Email/websitesEmail/websites

User curiosityUser curiosity Measures the average user is asked to take:Measures the average user is asked to take:

Patch operating systemPatch operating system

Install, enable, and update virus protectionInstall, enable, and update virus protection

Install, enable, and update firewallInstall, enable, and update firewall

Beware of adware and spyware.Beware of adware and spyware.

Ongoing debateOngoing debate: automation vs. education: automation vs. education


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Phishing & Web SpoofingPhishing & Web Spoofing

Because SSL makes intercepted messages virtuallyBecause SSL makes intercepted messages virtuallyimpossible to break, determined attackers go after theimpossible to break, determined attackers go after theendpoints.endpoints.

Steal data from server/clientSteal data from server/client

Dupe clients into volunteering dataDupe clients into volunteering data

Email and website look legitimateEmail and website look legitimate

Convincing URLsConvincing URLs

Financial company websites are among the greatest atFinancial company websites are among the greatest at

risk.risk. Business based on trust.Business based on trust.

Highest potential payoff for attacker.Highest potential payoff for attacker.


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AntiAnti--Phishing MechanismPhishing Mechanism


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Securing the ServerSecuring the Server


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Physical SecurityPhysical Security

The majority of attacks originateThe majority of attacks originate internallyinternally..

As with Web access, physical accessAs with Web access, physical access

should be kept to the minimum requiredshould be kept to the minimum required

((least privilegeleast privilege).).

Though physical security needs varyThough physical security needs vary

dramatically, every organization should:dramatically, every organization should:

Have a physical security planHave a physical security plan Have a disaster security planHave a disaster security plan

Have a (data) backup plan, includingHave a (data) backup plan, including

verification.verification.

Contingency plans for loss of service, staff.Contingency plans for loss of service, staff.


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Backing up DataBacking up Data

You cant predict the next emergency, soYou cant predict the next emergency, so

making regular backups is vital.making regular backups is vital.

Means of backup will depend on budget,Means of backup will depend on budget,

value of data, amount of datavalue of data, amount of data

CD backupsCD backups

Tape backupsTape backups

RAIDRAID

Back up anything unique to your system.Back up anything unique to your system.

Performing the backup is notPerforming the backup is not

enoughdoes the backup actually work???enoughdoes the backup actually work???


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Secure OperationSecure Operation

The longer a computer is run, the lessThe longer a computer is run, the lesssecure it becomes.secure it becomes.

As a system administrator, be sure to:As a system administrator, be sure to:

Patch your systemPatch your system Keep informed of known vulnerabilitiesKeep informed of known vulnerabilities

Keep and rotate logsKeep and rotate logs

Turn off unnecessary servicesTurn off unnecessary services

Of course, backupsOf course, backups

Utilize security toolsUtilize security tools TripwireTripwire intrusion & change detectionintrusion & change detection

KSAKSA snapshot & network scanningsnapshot & network scanning


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More on Access ControlsMore on Access Controls

3 Ways to restrict access3 Ways to restrict access Hidden URLsHidden URLs

HostHost--Based restrictionsBased restrictions

IdentityIdentity--Based restrictionsBased restrictions

An example .htaccess file in Apache:An example .htaccess file in Apache:AuthUserFile /home/jgrady/htpasswd/.htpasswdAuthUserFile /home/jgrady/htpasswd/.htpasswd

AuthName Admin SectionAuthName Admin Section

AuthType BasicAuthType Basic

order deny,alloworder deny,allow

deny from alldeny from all

allow from 71.240.12allow from 71.240.12

require user homeworkrequire user homework


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Securing WebSecuring Web

ApplicationsApplications


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Securing Web AppsSecuring Web Apps -- OverviewOverview

CGI, scripting languages, and server modules notCGI, scripting languages, and server modules notonly extend functionality, but also risk.only extend functionality, but also risk.

Keys to writing secure codeKeys to writing secure code

Design carefully

Design carefully

Have someone else look at your designHave someone else look at your design

Code and test iterativelyCode and test iteratively

Validate all userValidate all user--provided valuesprovided values manymanybugsbugs

arise because of unexpected input.arise because of unexpected input. Check arguments to OS functions and returnCheck arguments to OS functions and return

codes.codes.

Write to a dedicated log file.Write to a dedicated log file.

Reuse (trusted) code.Reuse (trusted) code.


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CrossCross--Side Scripting (XSS)Side Scripting (XSS)

An attack that exploits vulnerabilities inAn attack that exploits vulnerabilities indynamically Web pagesdynamically Web pages ---- lack of validationlack of validation

ExampleExample: Simple check using alert( );: Simple check using alert( );

alert(Whoops);alert(Whoops);

If the above works, then its possible for anIf the above works, then its possible for an

attacker to grab cookiesvia a remote script.attacker to grab cookiesvia a remote script.

In PHP, simply passing the above throughIn PHP, simply passing the above throughfilter_input( ) would prevent the XSS.filter_input( ) would prevent the XSS.

Additionally, validating the response is aAdditionally, validating the response is a

good idea.good idea.


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SQL InjectionsSQL Injections

Passing code into an application that was notPassing code into an application that was not

intended by the developerintended by the developer

Takes advantage of poor input validation &Takes advantage of poor input validation &

other improper codingother improper coding

May also exploit overMay also exploit over--privileged databaseprivileged database

accounts, gaining unauthorized access to dataaccounts, gaining unauthorized access to data

and OS resourcesand OS resources ExampleExample: Type OR = into password field.: Type OR = into password field.

Scarier exampleScarier example::

'exec master..xp_cmdshell 'net'exec master..xp_cmdshell 'netuseruser hacker1 nopassword /ADD'hacker1 nopassword /ADD'----


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Securing PHPSecuring PHP -- ConfigurationConfiguration

The php.ini file gives you control over PHPsThe php.ini file gives you control over PHPsbehavior.behavior.

Some best practicesSome best practices D

o not install the standalone binary in the cgiD

o not install the standalone binary in the cgi--bin;bin;install it outside the web servers hierarchy.install it outside the web servers hierarchy.

Install only those modules that are absolutelyInstall only those modules that are absolutelyneeded.needed.

Set display_errors = off; log_errors=on;Set display_errors = off; log_errors=on;

Set register_globals=off;Set register_globals=off; Look for any files named or titled phpinfo*,Look for any files named or titled phpinfo*,

and remove themand remove them there is no need tothere is no need toadvertise this information.advertise this information.


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Securing Your PHP CodeSecuring Your PHP Code

Again, validate input, especially whenAgain, validate input, especially when

Building SQL strings.Building SQL strings.

Running file commands.Running file commands.

Running system commands.Running system commands.

Check user credentials on each page.Check user credentials on each page.

Protect session IDs by usingProtect session IDs by using

session_regenerate_id( )session_regenerate_id( ) function.function.

PHP website suggests hiding your code byPHP website suggests hiding your code by

making it look like some other file type (e.g.,making it look like some other file type (e.g.,

.html).html)

Security by obscurity is weak.Security by obscurity is weak.


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Threats to AvailabilityThreats to Availability

An attacker does not have to steal data toAn attacker does not have to steal data tocause economic loss.cause economic loss.

DenialDenial--ofof--serviceservice

Preventing a web server from servingPreventing a web server from servingrequests.requests.

Attacks can be on CPU, memory, or disk.Attacks can be on CPU, memory, or disk.

Can also the result of accidents orCan also the result of accidents ornegligence.negligence.

Buffer overflowsBuffer overflows Caused by making erroneous assumptionsCaused by making erroneous assumptions

about the length of user input.about the length of user input.

User input is larger than preUser input is larger than pre--allocatedallocatedmemormemor


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Final ThoughtsFinal Thoughts

Like testing & documentation, security isLike testing & documentation, security isthe responsibility ofthe responsibility ofall team membersall team members.. Multiple minds find more potential risks.Multiple minds find more potential risks.

Blurring of the boundaries betweenBlurring of the boundaries betweenapplication and platform.application and platform.

If nothing else, rememberIf nothing else, remember Backup frequently!Backup frequently!

Validate user input!Validate user input! Keep yourOS and security software upKeep yourOS and security software up--toto--

datedate

Use the concept of least privilegeUse the concept of least privilege


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lecture 12. web application security

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