Introduction to Network Security
© N. Ganesan, Ph.D.
Acknowledgement
What is a Firewall?*
• A firewall, in general, isolates two
networks from one another to enforce
security
• A network in this case may consist of one
or more computers
• The firewall inspects each individual
“packet” of data as it arrives at either
side of the firewall — inbound or
outbound and determines whether the
data packet should be allowed to pass
Types of Firewall
• Hardware based
• Software based
Hardware Firewalls
• CISCO
• Dlink
• Linksys
Software Firewalls
• Zone Alarm Pro
General Firewall Features
• Port Control, Network Address Translation,
Application Monitoring (Program Control)
and Packet Filtering.
• Additional features: Data encryption, hiding
presence, reporting/logging, e-mail virus
protection, pop-up ad blocking, cookie
digestion, spy ware protection, laptop
protection.
• Note that different features may be available
in hardware and software firewalls
Do Firewalls Prevent Viruses and
Trojans?*
• NO!! A firewall can only prevent a virus or
Trojan from accessing the internet while on
your machine.
• 95% of all viruses and Trojans are received
via e-mail, through file sharing (like Kazaa or
Gnucleus) or through direct download of a
malicious program.
• Firewalls can't prevent this - only a good antivirus software program can.
Firewall Protection for Viruses and
Trojans*
• However, once installed on your PC, many
viruses and Trojans "call home" using the
internet to the hacker that designed it.
• This lets the hacker activate the Trojan and
he/she can now use your PC for his/her own
purposes.
• A firewall can block the call home and can
alert you if there is suspicious behavior
taking place on your system.
Some Hardware Firewall Features*
• Offers IP security and internet key
exchange network encryption.
• Integrated firewall functions.
• Network address translation.
• Encrypted SNMP management traffic.
Some Software Firewalls
• Zone Alarm
• Microsoft
• Mcafee
• Norton
Basic Types
• Network Layer
• Application Layer
Network Layer
• Makes decision based on the source,
destination addresses, and ports in
individual IP packets.
• Based on routers.
• Has the ability to perform static and
dynamic packet filtering and stateful
inspection.
Static & Dynamic Filtering
• Static Packet Filtering looks at minimal
information in the packets to allow or
block traffic between specific service
ports. Offers little protection.
• Dynamic Packet Filtering maintains a
connection table in order to monitor
requests and replies.
Stateful inspection
• Compares certain key parts of the
packet to a database of trusted
information. Incoming information is
compared to outgoing information
characteristics. Information is allowed
through only If comparison yields a
reasonable match.
Application Layer
• They are generally, hosts running proxy
servers which perform logging and
auditing of traffic through the network.
• Logging and access control are done
through software components.
Proxy Services
• Application that mediates traffic
between a protected network and the
internet.
• Able to understand the application
protocol being utilized and implement
protocol specific security.
• App. Protocols include: FTP, HTTP,
Telnet etc.
Port Scans
• When hackers remotely spy on your
computers to see what software and
services they have.
• Port scans are common but with a
properly configured and maintained
firewall you can restrict access.
DMZ
• Demilitarized zone
• Neither part of the internal network nor
part of the Internet
• Never offer attackers more to work with
than is absolutely necessary
Firewall Scenario
• Microsoft Internet Security and
Acceleration (ISA) Server as a Dedicated
Server
Network Configuration
Local Area Network
• Single Computer
• Small Office Network
– Less than 250 Clients
– IP Network Protocol
– Demand Dial Connectivity
• Larger Organization
– Array of ISA Server
ISA Server
Internet
Opening Ports
Software
• Firewall Windows
– Zone Alarm
– Winroute
– Trojan Trap - Trojan Horse
• Firewall Linux
– Iptables
• Firewall Mac
– Netbarrier
Implementing Firewall –
An Example
• Using Winroute as a software router for
a small LAN.
• Using Trojan Trap as protection against
active code attack.
• Software installation.
• Firewall configuration.
• Test and scan.
Firewall software comparison
Winroute
• Routing using NAT(Network Address
Translation)
• Packet filtering
• Port mapping
• Anti-spoofing
• VPN support
• DNS, DHCP
• Remote adminstration
Configuration and Rule Sets
•
Setup Winroute for LAN
• Winroute-PC should at least have 2
NICs
• Check that all IP addresses are pingable
• Validate NAT on the Winroute-PC
• Deactivate NAT on the NIC connected
to internal LAN
Setup Winroute for LAN
• No gateway configured on your local
interface of the Winroute-PC
• Configure forwarding options
• On each internal PC configure the
default gateway
• On each internal PC configure the DNS
server
Scan and Test
• http://scan.sygatetech.com/
• http://www.csnc.ch/onlinetests/
• http://grc.com/
• http://hackerwhacker.com/
Trojan Trap
• Resources protection – restrict access to
system resources by unknown
application
• Application control
• Content filtering
• IP ports monitoring
Hardware Firewall
•
•
•
•
•
What is it?
What it does.
An example.
Firewall use.
What it protects you from.
Hardware Firewall (Cont.)
•
What is it?

It is just a software firewall running on a dedicated
piece of hardware or specialized device.
Basically, it is a barrier to keep destructive forces
away from your property.
You can use a firewall to protect your home
network and family from offensive Web sites and
potential hackers.


Hardware Firewall (Cont.)
• What it does !
 It is a hardware device that filters the
information coming through the Internet
connection into your private network or
computer system.
 An incoming packet of information is flagged by
the filters, it is not allowed through.
Hardware Firewall (Cont.)
• An example !
Hardware Firewall (Cont.)
• Firewalls use:
 Firewalls use one or more of three methods to control
traffic flowing in and out of the network:
– Packet filtering
– Proxy service
– State-full inspection
Hardware Firewall (Cont.)
• Packet filtering - Packets are analyzed against a set of
filters.
• Proxy service - Information from the Internet is
retrieved by the firewall and then sent to the requesting
system and vice versa.
• State-full inspection – It compares certain key parts
of the packet to a database of trusted information.
Information traveling from inside to the outside is
monitored for specific defining characteristics, then
incoming information is compared to these
characteristics.
Hardware Firewall (Cont.)
• What it protects you from:
–
–
–
–
–
–
–



Remote logins
Application backdoors
SMTP session hijacking
E-mail Addresses
Spam
Denial of service
E-mail bombs
E-mail sent 1000’s of times till mailbox is full
Macros
Viruses
Software Firewall
• What it is?
– Also called Application Level Firewalls
– It is firewall that operate at the Application
Layer of the OSI
– They filter packets at the network layer
– It Operating between the Datalink Layer and
the Network Layer
– It monitor the communication type (TCP,
UDP, ICMP, etc.) as well as the origination of
the packet, destination port of the packet, and
application (program) the packet is coming
from or headed to.
Software Firewall (Cont.)
• How does software firewall works ?
Software Firewall (Cont.)
• Benefit of using application firewalls:
–
–
–
–
–
–
allow direct connection between client and host
ability to report to intrusion detection software
equipped with a certain level of logic
Make intelligent decisions
configured to check for a known Vulnerability
large amount of logging
Software Firewall (Cont.)
• Benefit of application firewalls (Cont.)
 easier to track when a potential vulnerability happens
 protect against new vulnerabilities before they are found
and exploited
 ability to "understand" applications specific information
structure
 Incoming or outgoing packets cannot access services for
which there is no proxy
Software Firewall (Cont.)
• Disadvantage of Firewall:
 slow down network access dramatically
 more susceptible to distributed denial of service (DDOS)
attacks.
 not transparent to end users
 require manual configuration of each client computer
Top Picks Personal Firewalls
• Norton Personal Firewall
• ZoneAlarm Free/Plus/Pro
Conclusion
Web References
•
•
•
•
•
•
•
firewall.com
firewall-net.com
firewallguide.com
msdn.microsoft.com
winroute.com
tinysoftware.com
sunsite.unc.edu
Benefits of Firewall-Summary
• Prevent intrusion
• Choke point for security audit
• Reduce attacks by hackers
• Hide network behind a single IP
address
• Part of total network security policy
References
http:// www.howstuffworks.com
http://www.microsoft.com
http://www.securityfocus.com
http://grace.com/us-firewalls.htm
http://www.kerio.com/us/supp_kpf_manual.
html
http://www.broadbandreports.com/faq/secur
ity/2.5.1.
http://www.firewall-software.com
Hacking
© N. Ganesan, Ph.D.
IP Spoofing
• IP spoofing is when an attacker captures the
routing packets to redirect a file or transmission to
a different destination.
• The technique is also effective in disguising an
attacker's identity.
• Protocols that deal with inter-computer
communication are most susceptible to
spoofing,e.g., ICMP, IGMP and UDP.
• Solution is securing transmission packets and
establishing screening policies, point to point
encryption, configuring network to reject packets
that claim to originate from a local address.
FTP Attacks
One of the most common FTP attacks is a buffer
overflow caused by a malformed command.
A successful attack could either drop the attacker in
a command shell or cause a denial of service.
Failure to apply the frequently released system
upgrades and patches is the most common cause of
FTP vulnerabilities.
FTP exploits are also useful in password guessing ,
FTP bounce attacks, and mining information (such
as the machine's registry).
Unix Finger Exploits
The Unix OS finger utility was used as an efficient
way to share user information in the early days of
the Internet.
To an attacker, the Finger utility can yield valuable
information, including user names, logons and
contact information.
It also provides a pretty good indication of users'
activities like how many times they are logged on.
The personal information it reveals can provide an
attacker with enough of a framework to trick
legitimate users into revealing passwords and
access codes.
Flooding and Broadcasting
An attacker can significantly reduce the processing
capacity of a network by sending more information
requests than it can handle-a classic denial of
service.
Sending a large amount of requests to a single port
is Flooding. When the requests are sent to all
network stations, it's called broadcasting.
 Attackers will often use flood attacks to gain access
to a system for use against other networks in
distributed denial-of-service (DDoS) campaigns.
DDoS attacks are harder to stop because they come
from multiple IP addresses simultaneously. The
only solution is to trace the packets back to their
source and shutdown the transmitting networks.
Fragmented Packet Attacks
Internet messages transmitted via TCP/IP can be
divided into packets in such a way that only the
first packet contains the TCP segment header
information.
Some firewalls will allow the processing of
subsequent packets that do not contain the same
source address information as the first packet,
which can cause any type of system to crash.
Fragmented packets can also create a flood-like
situation because they are stored in the Kernel. The
server will crash if the kernel memory absorbs too
many fragmented packets.
Solution : Firewall Filters
Email Exploits
E-mail exploits come in five forms: mail floods,
command manipulations, transport-level attacks,
malicious code insertion and social engineering.
Mail-flood attacks occur when so much mail is sent
to a target that communication programs destabilize
and crash the system.
Command-manipulation attacks can cause a system
to crash by subverting the mail transfer agent with a
buffer overflow caused by entering a malformed
command.
Email Exploits (Contd…)
Transport-level attacks exploit the SMTP. An
attacker can cause a temporary error condition in
the target system by overloading an SMTP buffer
with more data than it can handle.
Malicious content is often propagated through email systems. Some viruses and worms will be
carried into a system appearing as a legitimate
attachment
Social engineering e-mails are an attacker's attempt
to trick a legitimate user into revealing sensitive
information or executing a task. E.g., posing as a
network administrator to get your password for
Password Attacks
The most common password attacks are guessing,
brute force, cracking and sniffing.
Password guessing involves entering common
passwords either manually or through programmed
scripts.
Brute-force logon attacks follow the same basic logic
as password guessing, but are faster and more
powerful.
Password cracking is a method for defeating the
protection of encrypted passwords stored in a
system's admin files.
Because an attacker needs a significant level of
access to launch this kind of attack, the best defense
Selective Program Insertions
A selective program insertion is when an attacker
places a destructive program—a virus, worm or
Trojan horse--on a target system.
Some network administrators are augmenting their
malware defenses with alternative technologies
such as behavior blockers, which stop suspicious
code based on behavior patterns, not signatures.
A time bomb, sometimes called a logic bomb, is an
inserted program that executes its malicious
payload on a predetermined time or date.
Port Scanning and Polling
Through port scanning and polling, an attacker can
observe the functions and defenses of various
system ports.
For example, scanning could be used to determine
whether default SNMP community strings are open
to the public, meaning information can be extracted
for use in a remote command attack.
TCP/IP Sequence Stealing & Packet
Interception
TCP/IP sequence stealing is the capturing of
sequence numbers, which can be used to
make an attacker's packets appear legitimate.
A successful TCP/IP attack could allow an
attacker to intercept transactions between
two organizations, providing an opportunity
for a man-in-the-middle attack.
In some versions of Secured Shell Service
Daemon (SSHD), only the public key is used
for authentication. If an attacker learns the
public key, he could create and insert forged
packets.
Observations and Suggestions
Various firms
Install firewall, but never upgrade them.
Do massive Website improvements without
making parallel security improvements.
The best way to safeguard a website from
attack is to approach security as the ongoing
challenge rather than a one time effort.
Port Scanning Using PortQry
• What is port scanning?
• Using PortQry
(the Portqry.exe command-line utility)
What Is Port Scanning?
• Network
applications use
TCP/UDP ports
• Clients connect to
applications using
ports
• Port scanning is the
process of checking
whether a port is
open
TCP
389
UDP
135
Transport
ICMP
IP
Internet
Ethernet
Network
TCP and UDP in
TCP/IP protocol architecture
Port Numbers
• The Well Known Ports are those from 0
through 1023.
• The Registered Ports are those from 1024
through 49151.
• The Dynamic and/or Private Ports are those
from 49152 through 65535.
http://www.iana.org/assignments/port-numbers
ftp://ftp.isi.edu/in-notes/rfc1700.txt
Well-know TCP / UDP ports
TCP Port Number
Description
20
FTP (Data Channel)
21
FTP (Control Channel)
23
Telnet
80
HyperText Transfer Protocol (HTTP)
used for the World Wide Web
139
NetBIOS session service
UDP Port Number
Description
53
Domain Name System (DNS) Name
Queries
69
Trivial File Transfer Protocol (TFTP)
137
NetBIOS name service
138
NetBIOS datagram service
161
Simple Network Management Protocol
(SNMP)
Port Scanning for TCP
• TCP ports use
"three-way
handshake"
• Successful
handshake means
port is listening
• TCP Reset packet
means port is not
listening
• No response means
port is filtered
TCP
389
Transport
ICMP
IP
Internet
Ethernet
Network
Port Scanning for UDP
• UDP ports do not use
"three-way handshake"
• Send UDP packet to
port and wait for
response
• Most applications will
not respond to zerolength packets
• Formatted packet is
necessary to get a
response
• Most port scanners do
not scan UDP ports
UDP
135
Transport
ICMP
IP
Internet
Ethernet
Network
What Is Port Scanning used for?
Use port scanning
to:
• Test connectivity
• Test security
query ports
Port Scanner App
Firewall
TCP 25: SMTP
TCP 80: WWW
UDP 135: RPC EPM
UDP 389: LDAP
Server
Using PortQry
• PortQry is designed as an
application layer port scanner
• It checks whether TCP and UDP
ports are open, closed, or filtered
• It determines if UDP ports are open
using packets formatted for well
known services
Portqry is available for download on the Microsoft Web site at:
http://download.microsoft.com/download/win2000adserv/Utility/1.0
/NT5/EN-US/portqry.exe
PortQry Supports:
•
•
•
•
•
•
•
•
LDAP
RPC
DNS
SMTP
POP3
IMAP4
FTP
NetBIOS Name Service
LDAP
RPC
EPM
TCP
389
UDP
135
Application
Session
Transport
ICMP
IP
Internet
Ethernet
Network
Status of a TCP/IP port
• Listening
– A process is listening on the port on the computer you choose.
Portqry.exe received a response from the port.
• Not Listening
– No process is listening on the target port on the target system.
Portqry.exe received an Internet Control Message Protocol (ICMP)
"Destination Unreachable - Port Unreachable" message back from
the target UDP port. Or if the target port is a TCP port, Portqry
received a TCP acknowledgement packet with the Reset flag set.
• Filtered
– The port on the computer you chose is being filtered.
Portqry.exe did not receive a response from the port. A
process may or may not be listening on the port. By default,
TCP ports are queried three times and UDP ports are
queried once before a report indicates that the port is
filtered.
PortQry Usage
portqry -n server [-p protocol] [-e || -r || -o endpoint(s)] [-l logfile] [s] [-q]
Where:
-n [server] IP address or name of server to query
-p [protocol] TCP or UDP or BOTH (default is TCP)
-e [endpoint] single port to query (valid range: 1-65535)
-r [end point range] range of ports to query (start:end)
-o [end point order] range of ports to query in an order (x,y,z)
-l [logfile] name of log file to create
-s 'slow link delay' waits longer for UDP replies from remote systems
-q 'quiet' operation runs with no output
returns 0 if port is listening
returns 1 if port is not listening
returns 2 if port is listening or filtered
portqry -n myserver -p UDP -e 389
Returns LDAP base query information
UDP port 389 (unknown service): LISTENING or FILTERED
Sending LDAP query to UDP port 389...
LDAP query response:
currentdate: 09/03/2001 05:42:40 (unadjusted GMT)
subschemaSubentry:
CN=Aggregate,CN=Schema,CN=Configuration,DC=eu,DC=reskit,DC=com
dsServiceName: CN=NTDS Settings,CN=RED-DC-11,CN=Servers,CN=NA-WARED,CN=Sites,CN=Configuration,DC=eu,DC=reskit,DC=com
namingContexts: DC=redmond,DC=eu,DC=reskit,DC=com
defaultNamingContext: DC=redmond,DC=eu,DC=reskit,DC=com
schemaNamingContext: CN=Schema,CN=Configuration,DC=eu,DC=reskit,DC=com
configurationNamingContext: CN=Configuration,DC=eu,DC=reskit,DC=com
rootDomainNamingContext: DC=eu,DC=reskit,DC=com
supportedControl: 1.2.840.113556.1.4.319
supportedLDAPVersion: 3
supportedLDAPPolicies: MaxPoolThreads
highestCommittedUSN: 4259431
supportedSASLMechanisms: GSSAPI
dnsHostName: myserver.eu.reskit.com
ldapServiceName: eu.reskit.com:myserver$@eu.RESKIT.COM
serverName:
CN=MYSERVER,CN=Servers,CN=Sites,CN=Configuration,DC=eu,DC=reskit,DC=com
supportedCapabilities: 1.2.840.113556.1.4.800
isSynchronized: TRUE
isGlobalCatalogReady: TRUE
======== End of LDAP query response ========
UDP port 389 is LISTENING
portqry -n myserver -p UDP -e 135
Dumps RPC EndPoint Mapper database
UDP port 135 (epmap service): LISTENING or FILTERED
Querying Endpoint Mapper Database...
Server's response:
UUID: 50abc2a4-574d-40b3-9d66-ee4fd5fba076
ncacn_ip_tcp:169.254.12.191[4144]
UUID: ecec0d70-a603-11d0-96b1-00a0c91ece30 NTDS Backup Interface
ncacn_np:\\\\MYSERVER[\\PIPE\\lsass]
UUID: e3514235-4b06-11d1-ab04-00c04fc2dcd2 MS NT Directory DRS Interface
ncacn_ip_tcp:169.254.12.191[1030]
UUID: e3514235-4b06-11d1-ab04-00c04fc2dcd2 MS NT Directory DRS Interface
ncadg_ip_udp:169.254.12.191[1032]
UUID: 12345678-1234-abcd-ef00-01234567cffb
ncacn_np:\\\\MYSERVER[\\PIPE\\lsass]
UUID: 12345678-1234-abcd-ef00-01234567cffb
ncacn_np:\\\\MYSERVER[\\PIPE\\POLICYAGENT]
Total endpoints found: 6
==== End of RPC Endpoint Mapper query response ====
UDP port 135 is LISTENING
portqry -n myserver -p UDP -e 53
• Verifies DNS query and response
operation
UDP port 53 (domain service): LISTENING or
FILTERED
Sending DNS query to UDP port 53...
UDP port 53 (domain service): LISTENING
portqry -n MyMailServer -p TCP -e 25
• Returns SMTP, POP3, IMAP4 status
messages
TCP port 25 (SMTP service): LISTENING
Data returned from the port:
220 MyMailServer.eu.reskit.com Microsoft ESMTP MAIL
Service, Version: 5.0.2195.2966 ready at Sun, 2 Sep 2001
23:24:30 -0700
portqry -n MyFtpServer -p TCP -e 21
• Returns FTP status message and tests
for anonymous account access
220 MyFtpServer Microsoft FTP Service (Version 5.0).
331 Anonymous access allowed, send identity (email name) as password.
portqry -n myserver -p UDP -e 137
• Verifies NetBIOS Name Service
functionality and returns MAC address
UDP port 137 (netbios-ns service): LISTENING or FILTERED
Attempting NETBIOS adapter status query to UDP port 137...
Server's response: MAC address 00c04f7946f0
UDP port: LISTENING
Query behavior configurable
using local service file
• Located in
%systemroot%/system32/drivers/etc/servic
e
• Resolves service name using this file
• Decides what type of query to send to
port using this file
References
• http://www.tlc.discovery.com/convergence/hacker
s/hackers.html
• http://www.tuxedo.org/~esr/faqs/hackerhowto.html
• http://www.iss.net/security_center/advice/Underg
round/Hacking/Methods/Technical/
• http://www.infosecuritymag.com/articles/march01
/features4_battle_plans.shtml
• http://www.nmrc.org/faqs/www/wsec09.html
• http://www.microsoft.com/. Tim Rains • Technical Lead •
Networking Team
• Q310099, "Description of the Portqry.exe CommandLine Utility"