advanced network security – firewall implementation and

8/14/2019 Advanced Network Security Firewall Implementation And

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Advanced Network SecurityAdvanced Network Security

Firewall Implementation andFirewall Implementation and

DesignDesignTerm: January 2005

Dana Epp

[email protected]

http://silverstr.ufies.org/blog/

COMP 4706
mailto:[email protected]:[email protected]


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AgendaAgendaAgendaAgenda

Review from last classReview from last class Group STRIDE analysisGroup STRIDE analysis Building a firewall port matrixBuilding a firewall port matrix

Introduction to NMAPIntroduction to NMAP Hands on - Scanning ports with NMAPHands on - Scanning ports with NMAP Hands on Creating basic firewall rules onHands on Creating basic firewall rules on

LinuxLinux


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Learning OutcomesLearning OutcomesLearning OutcomesLearning Outcomes

Identify various types of firewalls and theirIdentify various types of firewalls and their

functions, including which firewalls operate atfunctions, including which firewalls operate atwhich OSI protocol layer, and the basicwhich OSI protocol layer, and the basic

variations of firewall architecturesvariations of firewall architectures

Describe risk mitigation techniques to varyingDescribe risk mitigation techniques to varying

threats with the use of different firewallthreats with the use of different firewall

architecturesarchitectures

Demonstrate the ability to design and deployDemonstrate the ability to design and deploy

policies on a firewallpolicies on a firewall

On successful completion of this course,On successful completion of this course,students will be able to:students will be able to:


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Basic Types of FirewallsBasic Types of FirewallsBasic Types of FirewallsBasic Types of Firewalls

Packet filtering firewallsPacket filtering firewalls

Stateful packet inspection firewallsStateful packet inspection firewalls

Application proxiesApplication proxies HybridsHybrids


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Packet filterPacket filterPacket filterPacket filter

Source IP addressSource IP address

Destination IP addressDestination IP addressTCP/UDP source portTCP/UDP source port

TCP/UDP destination portTCP/UDP destination port

A packet filter firewall is the simplesttype of firewall. Dealing with eachindividual packet, the firewall applies

its rule set to determine which packetto allow or disallow. The firewallexamines each packet based on thefollowing criteria:


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Packet Filter - ProsPacket Filter - ProsPacket Filter - ProsPacket Filter - Pros

They are fast because they operate on IP addresses andThey are fast because they operate on IP addresses and

TCP/UDP port numbers alone, ignoring the data contentsTCP/UDP port numbers alone, ignoring the data contents

(payload) of packets.(payload) of packets.

Due to the fact that packet payload is ignored, applicationDue to the fact that packet payload is ignored, application

independence exists.independence exists.

Least expensive of the three types of firewalls.Least expensive of the three types of firewalls.

Packet filtering rules are relatively easy to configure.Packet filtering rules are relatively easy to configure.

There are no configuration changes necessary to theThere are no configuration changes necessary to the

protected workstations.protected workstations.


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Packet filters - ConsPacket filters - ConsPacket filters - ConsPacket filters - Cons

Allow a direct connection between endpoints throughAllow a direct connection between endpoints throughthe firewall. This leaves the potential for athe firewall. This leaves the potential for avulnerability to be exploited.vulnerability to be exploited.

There is no screening of packet payload available. ItThere is no screening of packet payload available. Itis impossible to block users from visiting web sitesis impossible to block users from visiting web sites

deemed off limits, for example.deemed off limits, for example. Logging of network traffic includes only IP addressesLogging of network traffic includes only IP addresses

and TCP/UDP port numbers, no packet payloadand TCP/UDP port numbers, no packet payloadinformation is available.information is available.

Complex firewall policies are difficult to implementComplex firewall policies are difficult to implement

using filtering rules alone.using filtering rules alone.

There is a reliance on the IP address forThere is a reliance on the IP address forauthentication rather than user authentication.authentication rather than user authentication.

Dynamic IP addressing schemes such as DHCP mayDynamic IP addressing schemes such as DHCP maycomplicate filtering rules involving IP addresses.complicate filtering rules involving IP addresses.


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Stateful packet inspectionStateful packet inspectionStateful packet inspectionStateful packet inspection

Examines the contents of packetsrather than just filtering them; thatis, they consider their contents as

well as their addresses.

Stateful packet inspection firewallsalso take into account the state ofthe connections they handle so that,for example, a legitimate incomingpacket can be matched with the

outbound request for that packet and


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Stateful packet inspectionStateful packet inspection

- Pros- ProsStateful packet inspectionStateful packet inspection

- Pros- Pros Offers improved security over basic packetOffers improved security over basic packet

filters due to packet examination.filters due to packet examination.

Offers a degree of application independence,Offers a degree of application independence,based on level of stateful packet examination.based on level of stateful packet examination.

Better logging of activities over basic packetBetter logging of activities over basic packetfilters.filters.

Good performance.Good performance.

Configuration changes to the protectedConfiguration changes to the protected

workstations are unnecessary.workstations are unnecessary.


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Stateful packet inspectionStateful packet inspection

- Cons- ConsStateful packet inspectionStateful packet inspection

- Cons- Cons Allow a direct connection betweenAllow a direct connection between

endpoints through the firewall. This leavesendpoints through the firewall. This leaves

the potential for a vulnerability to bethe potential for a vulnerability to be

exploited.exploited. No hiding of your private systems.No hiding of your private systems.

Setting up stateful packet examinationSetting up stateful packet examination

rules is more complicated.rules is more complicated.

Only supported protocols at theOnly supported protocols at theapplication layer.application layer.

No user authentication.No user authentication.


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Application proxiesApplication proxiesApplication proxiesApplication proxies

An application proxy is a programrunning on the firewall that emulatesboth ends of a network connection.

One can think of it as a sort of"translator" in-between the twocomputers communicating.


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Application proxies - ProsApplication proxies - ProsApplication proxies - ProsApplication proxies - Pros

Firewall does not let end pointsFirewall does not let end pointscommunicate directly with one another.communicate directly with one another.Thus a vulnerability in a protocol whichThus a vulnerability in a protocol whichcould slip by a packet filter or statefulcould slip by a packet filter or stateful

packet inspection firewall could bepacket inspection firewall could beovercome by the proxy program.overcome by the proxy program. Has the best content filtering capability.Has the best content filtering capability. Can hide private systems.Can hide private systems.

Robust user authentication.Robust user authentication. Offers the best logging of activities.Offers the best logging of activities. Policy rules are usually easier thanPolicy rules are usually easier than

packet filtering rules.packet filtering rules.


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Application proxies - ConsApplication proxies - ConsApplication proxies - ConsApplication proxies - Cons

Performance problems; much slower than the otherPerformance problems; much slower than the other

twotwo

Must have a proxy for every protocol. Failure to have aMust have a proxy for every protocol. Failure to have a

proxy may prevent a protocol from being handledproxy may prevent a protocol from being handled

correctly by the firewall.correctly by the firewall. TCP is the preferred transport. UDP may not beTCP is the preferred transport. UDP may not be

supported.supported.

Limited transparency, clients may need to be modified.Limited transparency, clients may need to be modified.

Setting up the proxy server in a browser, for example.Setting up the proxy server in a browser, for example.

No protection from all protocol weaknesses.No protection from all protocol weaknesses.


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OSI Open SystemOSI Open System

InterconnectInterconnectOSI Open SystemOSI Open System

InterconnectInterconnect


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TCP/IP ProtocolTCP/IP Protocol

ArchitectureArchitectureTCP/IP ProtocolTCP/IP Protocol

ArchitectureArchitecture


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Three way TCP handshakeThree way TCP handshakeThree way TCP handshakeThree way TCP handshake


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Common Ports andCommon Ports and

ServicesServicesCommon Ports andCommon Ports and

ServicesServices Windows: %windirWindows: %windir

%\System32\drivers\etc\services%\System32\drivers\etc\services Linux:Linux:

/etc/services/etc/services Examples:Examples:

SMTP = port 25SMTP = port 25

HTTP = port 80HTTP = port 80POP3 = port 110POP3 = port 110PPTP = port 1723PPTP = port 1723


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The STRIDE Threat ModelThe STRIDE Threat ModelThe STRIDE Threat ModelThe STRIDE Threat Model

Spoofing identitySpoofing identity Attacker obtains something that enables authenticationAttacker obtains something that enables authentication

Tampering with dataTampering with data Unauthorized change made to stored or in-transit informationUnauthorized change made to stored or in-transit information

RepudiationRepudiation Performing an illegal operation in a system that lacks the ability toPerforming an illegal operation in a system that lacks the ability to

trace such operationstrace such operations Information disclosureInformation disclosure

Exposing critical information to unauthorized individualsExposing critical information to unauthorized individuals

Denial of Service (DoS)Denial of Service (DoS) Denies service to othersDenies service to others

Elevation of privilegesElevation of privileges

Attacker exploits a weakness to gain greater privileges on a systemAttacker exploits a weakness to gain greater privileges on a systemthan were intendedthan were intended


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Ranking and PrioritizingRanking and Prioritizing

ThreatsThreatsRanking and PrioritizingRanking and Prioritizing

ThreatsThreats

Chance of attack occurringChance of attack occurring 1 = high1 = high 10 = low10 = low

How much effort/cost/time is needed toHow much effort/cost/time is needed tolaunch the attack?launch the attack?

What is the cost/damage if it occurs?What is the cost/damage if it occurs? 1 = little1 = little 10 = massive10 = massive

RISK = Damage / ChanceRISK = Damage / Chance Goal is to reduce riskGoal is to reduce risk Do high risk items firstDo high risk items first


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How to Respond toHow to Respond to

ThreatsThreatsHow to Respond toHow to Respond to

ThreatsThreats

1.1. Do nothing.Do nothing.

2.2. Inform the user of the threat.Inform the user of the threat.

3.3. Remove the problem.Remove the problem.4.4. Fix the problem.Fix the problem.


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Defense in DepthDefense in DepthDefense in DepthDefense in Depth

Assume external systems are insecureAssume external systems are insecure Were secure, we have a firewall *ugh*Were secure, we have a firewall *ugh*

Assume your system(s) is the last thingAssume your system(s) is the last thingstandingstanding Plan on failurePlan on failure

More layers of security means more work toMore layers of security means more work tocompromise a targetcompromise a targetThreat risk goes down as threat difficulty goes upThreat risk goes down as threat difficulty goes up

Never depend on security through obscurityNever depend on security through obscurity


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Group STRIDEGroup STRIDE

AnalysisAnalysisGroup STRIDEGroup STRIDE

AnalysisAnalysis


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Building a firewall portBuilding a firewall port

matrixmatrixBuilding a firewall portBuilding a firewall port

matrixmatrix Determine trust zonesDetermine trust zones

Determine ports that need openingDetermine ports that need opening

Determine packet type (tcp/udp)Determine packet type (tcp/udp) Determines direction of packet flowDetermines direction of packet flow

Determine any limitations you canDetermine any limitations you can

set on src/dstset on src/dst


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LUNCLUNCHHLUNCLUNC

HH


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Introduction to NMAPIntroduction to NMAPIntroduction to NMAPIntroduction to NMAP

Can scan networks to find active (online) hostsCan scan networks to find active (online) hosts

Can scan hosts to find open portsCan scan hosts to find open ports

Can send crafted packets to fingerprint theCan send crafted packets to fingerprint the

operating systemoperating system

Can be used defensively to identifyCan be used defensively to identify

weaknesses that need to be corrected, orweaknesses that need to be corrected, or

offensively by an attacker to probe foroffensively by an attacker to probe forvulnerabilities to exploit.vulnerabilities to exploit.


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Interesting NMAP optionsInteresting NMAP optionsInteresting NMAP optionsInteresting NMAP options

-v = Verbose logging-v = Verbose logging

-O = OS fingerprinting-O = OS fingerprinting

-sS = SYN stealth scan-sS = SYN stealth scan

-P0 = Scan without ping probes-P0 = Scan without ping probes

nmap v O sS your.host.comnmap v O sS your.host.com


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Introduction to iptablesIntroduction to iptablesIntroduction to iptablesIntroduction to iptables

33rdrd generation firewall on Linuxgeneration firewall on Linux

Supports basic packet filtering asSupports basic packet filtering as

well as connection state trackingwell as connection state tracking

For our needs for this course, weFor our needs for this course, we

will use simple/basic packetwill use simple/basic packetfilteringfiltering


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Introduction to iptablesIntroduction to iptablesIntroduction to iptablesIntroduction to iptables# Sample firewall incomplete do not use. For discussion only

IPTABLES=/sbin/iptablesANY=0.0.0.0/0

ETHIP=10.10.1.1

ADMINNOC=10.10.1.250

# Flush chains

$IPTABLES --flush

# Set default policies$IPTABLES -P INPUT ACCEPT

$IPTABLES -P OUTPUT ACCEPT

$IPTABLES -P FORWARD ACCEPT

# Allow SSH from admin NOC

$IPTABLES -A INPUT -p tcp -s $ADMINNOC --sport 1024:65534 --dport 22 -j ACCEPT

$IPTABLES -A OUTPUT -p tcp -d $ADMINNOC -sport 22 --dport 1024:65534 -j ACCEPT

# Allow Web access

$IPTABLES -A INPUT -p tcp --dport 80 -j ACCEPT

# Allows secure web access

$IPTABLES -A INPUT -p tcp --dport 443 -j ACCEPT

$IPTABLES -A INPUT -j DROP


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Dropping vs RejectingDropping vs Rejecting

PacketsPacketsDropping vs RejectingDropping vs Rejecting

PacketsPackets Rejecting packets COULD resource starveRejecting packets COULD resource starve

your systemyour system

Dropping packets could cause networkDropping packets could cause networkdiagnostic hell for the other end if youdiagnostic hell for the other end if youdont respond nicelydont respond nicely

Danas Law: It is better to DROP packetsDanas Law: It is better to DROP packetsand buy your favorite network admin aand buy your favorite network admin abeer than to REJECT and have alarms gobeer than to REJECT and have alarms gooff at 2 in the morning during a DoS,off at 2 in the morning during a DoS,waking you up.waking you up.


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Hands onHands onLABLABHands onHands onLABLAB


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Good readingGood readingGood readingGood reading

IPTables Packet Filtering HOWTOIPTables Packet Filtering HOWTOhttp://netfilter.org/documentation/HOWTO/packet-filtering-HOWTO.htmlhttp://netfilter.org/documentation/HOWTO/packet-filtering-HOWTO.html

Building Internet FirewallsBuilding Internet Firewalls

ISBN:1-56592-124-0ISBN:1-56592-124-0

Linux FirewallsLinux FirewallsISBN: 0-7357-0900-9ISBN: 0-7357-0900-9

Threat ModelingThreat Modeling

ISBN: 0-7356-1991-3ISBN: 0-7356-1991-3


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Any Questions?Any Questions?

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