csce 815 network security lecture 22 intrusions april 10, 2003

CSCE 815 Network Security CSCE 815 Network Security Lecture 22 Lecture 22CSCE 815 Network Security CSCE 815 Network Security Lecture 22 Lecture 22

IntrusionsIntrusions

April 10, 2003

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Protocol ReviewProtocol Review

IP internet protocol – routing packets through networkIP internet protocol – routing packets through network

TCP – connection oriented transportTCP – connection oriented transport

UDP – UDP –

ARP – address resolution protocol ***ARP – address resolution protocol ***

ICMP – internet control message protocol ***over IPICMP – internet control message protocol ***over IP

DHCP - DHCP -

Application layer – FTP, HTTP, SMTP, SNMP, SSHApplication layer – FTP, HTTP, SMTP, SNMP, SSH

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Buffer Overflow commentsBuffer Overflow comments

GDBGDB

gcc –g gcc –g

breakpointsbreakpoints

single stepsingle step

info [frame, regs, …]info [frame, regs, …]

print [format] variableprint [format] variable

Linux vs CYGWINLinux vs CYGWIN

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IP Spoofing AttacksIP Spoofing Attacks

Spoofing means fraudulently authenticating one Spoofing means fraudulently authenticating one machine as anothermachine as another

Fraudulent send IP packet to A with Fraudulent send IP packet to A with

source IP address field=“IP address of B”source IP address field=“IP address of B”

Raw sockets - Raw sockets -

Blind Spoofing: TCP handshake guessing sequence Blind Spoofing: TCP handshake guessing sequence numbersnumbers

““Exploit code for IP Smart Spoofing ”Exploit code for IP Smart Spoofing ”

http://www.mail-archive.com/bugtraq@securityfocushttp://www.mail-archive.com/bugtraq@securityfocus. . com/msg09855.htmlcom/msg09855.html

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Raw Socket CreationRaw Socket Creation

Reference Stevens “Unix Network Programming” Ch 25Reference Stevens “Unix Network Programming” Ch 25#include <socket.h>

int sockfd;

1.1. Create the raw socketCreate the raw socketsockfd = socket(AF_INET, SOCK_RAW, protocol)

2.2. The IP_HDRINCL socket option can be setThe IP_HDRINCL socket option can be setint on = 1;

setsocketopt(sockfd, IPPRTO_IP, IP_HDRINCL, &on sizeof(on))

3.3. Bind(sockfd, &addr, sizeof(addr))Bind(sockfd, &addr, sizeof(addr))

4.4. Sendto(sockfd, sendbuf, len,0, dstAddr, dstAddrLen)Sendto(sockfd, sendbuf, len,0, dstAddr, dstAddrLen)

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Preventing IP Spoofing AttacksPreventing IP Spoofing Attacks

Preventing IP spoofingPreventing IP spoofing

have your routers reject packets with local have your routers reject packets with local addresses from the outsideaddresses from the outside

also have them reject internal packets claiming to also have them reject internal packets claiming to originate from the outsideoriginate from the outside

authenticate packets from insideauthenticate packets from inside

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ARP SpoofingARP Spoofing

Address resolution Protocol (ARP)Address resolution Protocol (ARP)

IP address IP address hardware(ethernet) address mapping hardware(ethernet) address mapping

send ARP packet “who has IP address and what is send ARP packet “who has IP address and what is your hardware address?”your hardware address?”

ARP cache – table of recent responsesARP cache – table of recent responses


1.1. Assume IP address “a” of trusted hostAssume IP address “a” of trusted host

2.2. Respond to ARP packets for address “a”Respond to ARP packets for address “a”

3.3. Sending false hardware address (I.e. the fraud’s Sending false hardware address (I.e. the fraud’s address)address)

Solution: make ARP cache static (manual updates!?!)Solution: make ARP cache static (manual updates!?!)

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Address resolution Protocol (ARP)Address resolution Protocol (ARP)

IP address IP address hardware(ethernet) address mapping hardware(ethernet) address mapping

send ARP packet “who has IP address and what is send ARP packet “who has IP address and what is your hardware address?”your hardware address?”

ARP cache – table of recent responsesARP cache – table of recent responses


1.1. Assume IP address “a” of trusted hostAssume IP address “a” of trusted host

2.2. Respond to ARP packets for address “a”Respond to ARP packets for address “a”

3.3. Sending false hardware address (I.e. the fraud’s Sending false hardware address (I.e. the fraud’s address)address)

Solution: make ARP cache static (manual updates!?!)Solution: make ARP cache static (manual updates!?!)

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DNS SpoofingDNS Spoofing

Domain Name System (DNS)Domain Name System (DNS) hierarchical name servers map FQDN IP address UDP packet sent with name to name server

Chinese dissidents SpoofingChinese dissidents Spoofing

http://www.dit-inc.us/hj-09-02.htmlhttp://www.dit-inc.us/hj-09-02.html

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Web SpoofingWeb Spoofing

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Email SpoofingEmail Spoofing

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Security MythSecurity Myth

““The only secure computer is the one that is turned off The only secure computer is the one that is turned off and unplugged”and unplugged”

Once connected to internet it becomes a targetOnce connected to internet it becomes a target

So shutdown all unnecessary services.So shutdown all unnecessary services.

Myth 2 “My firewall will stop the pesky crackers!”Myth 2 “My firewall will stop the pesky crackers!”

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The Players, Platforms and AttacksThe Players, Platforms and Attacks

The Players:The Players: The Black Hats Script kiddies The White Hats

Platforms of attackersPlatforms of attackers1. Windows2. Linux/NetBSD/FreeBSD3. OpenBSD billed as “the most secure OS freely available”

AttacksAttacks Denial of Service Viruses, Trojans, malicious scripts Web defacement

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Network Administrator ToolsNetwork Administrator Tools

Network Administration toolsNetwork Administration tools (MSDOS/Windows) ipconfig ifconfig netstat /etc/… not really tools as much as files /sbin/…

Find ethernet/IP addressesFind ethernet/IP addresses

More toolsMore tools http://newsforge.com/newsforge/02/12/12/0232235.shtml?tid

=23

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ARP Spoofing RevisitedARP Spoofing Revisited

Linux WorldLinux World

/sbin/sbin arp Iptables, ipchains, ipfwadm

Arp comand –print the tableArp comand –print the table

Ping somewhere then use arp to look at the table againPing somewhere then use arp to look at the table again

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What is a Firewall?What is a Firewall?

a a choke pointchoke point of control and monitoring of control and monitoring

interconnects networks with differing trustinterconnects networks with differing trust

imposes restrictions on network servicesimposes restrictions on network services only authorized traffic is allowed

auditing and controlling accessauditing and controlling access can implement alarms for abnormal behavior

is itself immune to penetrationis itself immune to penetration

provides provides perimeter defenceperimeter defence

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Firewall LimitationsFirewall Limitations

cannot protect from attacks bypassing itcannot protect from attacks bypassing it eg sneaker net, utility modems, trusted organisations,

trusted services (eg SSL/SSH)

cannot protect against internal threatscannot protect against internal threats eg disgruntled employee

cannot protect against transfer of all virus infected cannot protect against transfer of all virus infected programs or filesprograms or files because of huge range of O/S & file types

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Firewalls – Packet FiltersFirewalls – Packet Filters

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simplest of components simplest of components

foundation of any firewall system foundation of any firewall system

examine each IP packet (no context) and permit or deny examine each IP packet (no context) and permit or deny according to rules according to rules

hence restrict access to services (ports)hence restrict access to services (ports)

possible default policiespossible default policies that not expressly permitted is prohibited that not expressly prohibited is permitted

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Attacks on Packet FiltersAttacks on Packet Filters

IP address spoofingIP address spoofing fake source address to be trusted add filters on router to block

source routing attackssource routing attacks attacker sets a route other than default block source routed packets

tiny fragment attackstiny fragment attacks split header info over several tiny packets either discard or reassemble before check

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Firewalls with IPtables (Linux)Firewalls with IPtables (Linux)

IPtablesIPtables

IPchainsIPchains

NetfilterNetfilter

““10 minutes to an iptables-based Linux firewall”10 minutes to an iptables-based Linux firewall”by by Joshua DrakeJoshua Drake http://www.linuxworld.com/site-stories/2001/0920.ipchains.html

““Taming the Wild Netfilter”Taming the Wild Netfilter”September 01, 2001 by September 01, 2001 by David A. David A. BandelBandel http://www.linuxjournal.com/article.php?sid=4815

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[root@jd root]# /sbin/iptables -h[root@jd root]# /sbin/iptables -hiptables v1.2.1iptables v1.2.1Usage: iptables -[ADC] chain rule-specification [options]Usage: iptables -[ADC] chain rule-specification [options] iptables -[RI] chain rulenum rule-specification [options] iptables -[RI] chain rulenum rule-specification [options] iptables -D chain rulenum [options] iptables -D chain rulenum [options] iptables -[LFZ] [chain] [options] iptables -[LFZ] [chain] [options] iptables -[NX] chain iptables -[NX] chain iptables -E old-chain-name new-chain-name iptables -E old-chain-name new-chain-name iptables -P chain target [options] iptables -P chain target [options] iptables -h (print this help information) iptables -h (print this help information)

Commands:Commands:Either long or short options are allowed.Either long or short options are allowed. --append -A chain Append to chain --append -A chain Append to chain --delete -D chain Delete matching rule from chain --delete -D chain Delete matching rule from chain --delete -D chain rulenum --delete -D chain rulenum [...] [...]

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No incoming traffic (tcp connections)No incoming traffic (tcp connections) /sbin/iptables -A INPUT -p tcp --syn -j DROP

Accept incoming SSH (port 22) why?Accept incoming SSH (port 22) why? /sbin/iptables -A INPUT -p tcp --syn -s 192.168.1.110/32 --

destination-port 22 -j ACCEPT /sbin/iptables -A INPUT -p tcp --syn -j DROP

Add rule to allow a web server to the chainAdd rule to allow a web server to the chain /sbin/iptables -A INPUT -p tcp --syn -s 192.168.1.110/32 --

destination-port 22 -j ACCEPT /sbin/iptables -A INPUT -p tcp --syn --destination-port 80 -j

ACCEPT /sbin/iptables -A INPUT -p tcp --syn -j DROP

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Chroot JailsChroot Jails

References:References: http://librenix.com/ general purpose security/Linux site http://www.gsyc.inf.uc3m.es/~assman/jail/index.html

chroot environment: chroot environment:

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Chroot ImplementationChroot Implementation

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User-mode Linux User-mode Linux

UML (binding problem)UML (binding problem) http://user-mode-linux.sourceforge.net/

creates a virtual Machine creates a virtual Machine

allows you to run multiple instances of Linux on the allows you to run multiple instances of Linux on the same system at the same time same system at the same time

designed for a variety of purposes, such as kernel designed for a variety of purposes, such as kernel debugging, testing applications debugging, testing applications

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Firewalls – Stateful Packet FiltersFirewalls – Stateful Packet Filters

examine each IP packet in contextexamine each IP packet in context keeps tracks of client-server sessions checks each packet validly belongs to one

better able to detect bogus packets out of context better able to detect bogus packets out of context

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Firewalls - Application Level Gateway (or Proxy)Firewalls - Application Level Gateway (or Proxy)

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Firewalls - Application Level Gateway (or Proxy)Firewalls - Application Level Gateway (or Proxy)use an application specific gateway / proxy use an application specific gateway / proxy

has full access to protocol has full access to protocol user requests service from proxy proxy validates request as legal then actions request and returns result to user

need separate proxies for each service need separate proxies for each service some services naturally support proxying others are more problematic custom services generally not supported

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Firewalls - Circuit Level GatewayFirewalls - Circuit Level Gateway

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Firewalls - Circuit Level GatewayFirewalls - Circuit Level Gateway

relays two TCP connectionsrelays two TCP connections

imposes security by limiting which such connections imposes security by limiting which such connections are allowedare allowed

once created usually relays traffic without examining once created usually relays traffic without examining contentscontents

typically used when trust internal users by allowing typically used when trust internal users by allowing general outbound connectionsgeneral outbound connections

SOCKS commonly used for thisSOCKS commonly used for this

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Bastion HostBastion Host

highly secure host system highly secure host system

potentially exposed to "hostile" elements potentially exposed to "hostile" elements

hence is secured to withstand this hence is secured to withstand this

may support 2 or more net connectionsmay support 2 or more net connections

may be trusted to enforce trusted separation between may be trusted to enforce trusted separation between network connectionsnetwork connections

runs circuit / application level gateways runs circuit / application level gateways

or provides externally accessible services or provides externally accessible services

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Firewall ConfigurationsFirewall Configurations

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Access ControlAccess Control

given system has identified a user given system has identified a user

determine what resources they can accessdetermine what resources they can access

general model is that of access matrix withgeneral model is that of access matrix with subject - active entity (user, process) object - passive entity (file or resource) access right – way object can be accessed

can decompose bycan decompose by columns as access control lists rows as capability tickets

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Access Control MatrixAccess Control Matrix

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Trusted Computer SystemsTrusted Computer Systems

information security is increasingly important information security is increasingly important

have varying degrees of sensitivity of informationhave varying degrees of sensitivity of information cf military info classifications: confidential, secret etc

subjects (people or programs) have varying rights of access to subjects (people or programs) have varying rights of access to objects (information)objects (information)

want to consider ways of increasing confidence in systems to want to consider ways of increasing confidence in systems to enforce these rightsenforce these rights

known as multilevel securityknown as multilevel security subjects have maximum & current security level objects have a fixed security level classification

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Bell LaPadula (BLP) ModelBell LaPadula (BLP) Model

one of the most famous security modelsone of the most famous security models

implemented as mandatory policies on system implemented as mandatory policies on system

has two key policies: has two key policies:

no read upno read up (simple security property) (simple security property) a subject can only read/write an object if the current security level

of the subject dominates (>=) the classification of the object

no write downno write down (*-property) (*-property) a subject can only append/write to an object if the current security

level of the subject is dominated by (<=) the classification of the object

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Reference MonitorReference Monitor

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Evaluated Computer SystemsEvaluated Computer Systems

governments can evaluate IT systemsgovernments can evaluate IT systems

against a range of standards:against a range of standards: TCSEC, IPSEC and now Common Criteria

define a number of “levels” of evaluation with define a number of “levels” of evaluation with increasingly stringent checkingincreasingly stringent checking

have published lists of evaluated productshave published lists of evaluated products though aimed at government/defense use can be useful in industry also

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SummarySummary

have considered:have considered: firewalls types of firewalls configurations access control trusted systems

csce 815 network security lecture 22 intrusions april 10, 2003

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