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Network Security
Trish Miller
Objectives
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Types of Attacks
Attacks on the OSI & TCP/IP Model
Attack Methods
Prevention
Switch Vulnerabilities and Hacking
Cisco Routers
Interesting links
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Types of Attacks
• Physical Access
Attacks
– Wiretapping
– Server Hacking
– Vandalism
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• Dialog Attacks
– Eavesdropping
– Impersonation
– Message Alteration
Types of Attacks (Cont.)
• Penetration Attacks
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Scanning (Probing)
Break-in
Denial of Service
Malware
• Viruses
• Worms
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• Social Engineering
– Opening Attachments
– Password Theft
– Information Theft
Risk Analysis of the Attack
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What is the cost if the attack succeeds?
What is the probability of occurrence?
What is the severity of the threat?
What is the countermeasure cost?
What is the value to protect the system
Determine if the countermeasure should be
implemented.
• Finally determine its priority.
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OSI & TCP/IP Related
Attacks
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OSI Model Related Attacks
• Application layer:
– Attacks on web
– Attacks are typically
virus
• Presentation:
– Cracking of encrypted
transmissions by short
encryption key
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• Session
– Password theft
– Unauthorized Access
with Root permission
• Transport & Network:
– Forged TCP/IP
addresses
– DoS Attacks
OSI Model Related Attacks
• Data Link &
Physical
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Network Sniffers
Wire Taps
Trojan Horses
Malicious code
Attacks Related to TCP Packet
• Port Number
– Applications are identified by their Port
numbers
– Well-known ports (0-1023)
• HTTP=80, Telnet=23, FTP=21 for supervision,
20 for data transfer, SMTP=25
– Allows applications to be accessed by the
root user
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Attacks Related to TCP Packet
• IP address spoofing
– Change the source IP address
– To conceal identity of the attacker
– To have the victim think the packet comes
from a trusted host
– LAND attack
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Attacks Related to TCP Packet
• Port Number
– Registered ports (1024-49152) for any
application
– Not all operating systems uses these port
ranges, although all use well-known ports
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Attack Methods
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Attack Methods
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Host Scanning
Network Scanning
Port Scanning
Fingerprinting
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Attack Methods (Cont.)
• Host Scanning
– Ping range of IP addresses or use
alternative scanning messages
– Identifies victims
– Types of Host scanning
• Ping Scanning
• TCP SYN/ACK attacks
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Attack Methods (Cont.)
• Network Scanning
– Discovery of the network infrastructure
(switches, routers, subnets, etc.)
– Tracert and applications similar identifies all
routers along the route to a destination host
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Attack Methods (Cont.)
• Port Scanning
– Once a host is identified, scan all ports to find
out if it is a server and what type it is
– Two types:
• Server Port Scanning
– TCP
– UDP
• Client Port Scanning
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– NetBIOS
– Ports 135 – 139 used for NetBIOS ports used for file
and print services.
– GRC.com a free website that scan your pc for open
ports.
Attack Methods (Cont.)
• Fingerprinting
– Discovers the host operating system and
applications as well as the version
• Active (sends)
• Passive (listen)
– Nmap does all major scanning methods
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Attack Methods (Cont.)
• Denial-of-Service (DoS) Attacks
– Attacks on availability
– SYN flooding attacks overload a host or
network with connection attempts
– Stopping DoS attacks is very hard.
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Attack Methods (Cont.)
• The Break-In
– Password guessing
– Take advantage of unpatched vulnerabilities
– Session hijacking
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After the Compromise
• Download rootkit via TFTP
• Delete audit log files
• Create backdoor account or Trojan
backdoor programs
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After the Compromise (Cont.)
• Weaken security
• Access to steal information, do
damage
• Install malicious software (RAT, DoS
zombie, spam relay, etc.)
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Prevention
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Preventions
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Stealth Scanning
Access Control
Firewalls
Proxy Servers
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IPsec
Security Policies
DMZ
Host Security
Stealth Scanning
• Noisiness of Attacks
• Exposure of the Attacker’s IP Address
• Reduce the rate of Attack below the IDS
Threshold
• Scan Selective Ports
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Access Control
• The goal of access control is to prevent
attackers from gaining access, and stops them if
they do.
• The best way to accomplish this is by:
– Determine who needs access to the resources
located on the server.
– Decide the access permissions for each resource.
– Implement specific access control policies for each
resource.
– Record mission critical resources.
– Harden the server against attacks.
– Disable invalid accounts and establish policies
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Firewalls
• Firewalls are designed to
protect you from outside
attempts to access your
computer, either for the
purpose of
eavesdropping on your
activities, stealing data,
sabotage, or using your
machine as a means to
launch an attack on a
third party.
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Firewalls (Cont.)
• Hardware
– Provides a strong
degree of protection
from the outside world.
– Can be effective with
little or no setup
– Can protect multiple
systems
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• Software
– Better suite to protect
against Trojans and
worms.
– Allows you to
configure the ports you
wish to monitor. It
gives you more fine
control.
– Protects a single
system.
Firewalls
• Can Prevent
– Discovery
• Network
• Traceroute
– Penetration
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Synflood
Garbage
UDP Ping
TCP Ping
Ping of Death
Proxy
• A proxy server is a buffer between your
network and the outside world.
• Use an anonymous Proxy to prevent
attacks.
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IPSec
• Provides various security services for traffic at
the IP layer
• These security services include
– Authentication
– Integrity
– Confidentiality
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IPsec overview - how IPsec helps
Problem
How IPsec
helps
Details
Unauthorized
system access
Authentication,
tamperproofing
Defense in depth by isolating
trusted from untrusted
systems
Targeted
attacks of highvalue servers
Authentication,
tamperproofing
Locking down servers with
IPsec. Examples: HR
servers, Outlook® Web
Access (OWA), DC
replication
Eavesdropping
Authentication,
confidentiality
Defense in depth against
password or information
gathering by untrusted
systems
Government
guideline
compliance
Authentication,
confidentiality
Example: “All
communications between
financial servers must be
encrypted.”
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DMZ Image
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Host Security
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Hardening Servers
Cisco IOS
Upgrades and Patches
Unnecessary Services
Network Monitoring tools
Switch Vulnerabilities and
Hacking
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CDP Protocol
• Used to locate IP address, version, and
model.
• Mass amounts of packets being sent can
fake a crash
• Used to troubleshoot network, but should
be disabled.
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ARP Poisoning
• Give users data by poisoning ARP cache
of end node.
• MAC address used to determine
destination. Device driver does not check.
• User can forge ARP datagram for man in
the middle attack.
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SNMP
• SNMP manages the network.
• Authentication is weak. Public and
Private community keys are clear text.
• Uses UDP protocol which is prone to
spoofing.
• Enable SNMPv3 without backwards
compatibility.
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Spanning Tree Attacks
• Standard STP takes 30-45 seconds to
deal with a failure or Root bridge
change.
• Purpose: Spanning Tree Attack reviews
the traffic on the backbone.
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Spanning Tree Attacks
• Only devices affected by the failure
notice the change
• The attacker can create DoS condition
on the network by sending BPDUs
from the attacker.
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Spanning Tree Attacks (Cont.)
• STEP 1: MAC flood the access switch
• STEP 2: Advertise as a priority zero
bridge.
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SpanningTree
TreeAttacks
Attacks (Cont.)
(Cont.)
Spanning
• STEP 3: The attacker becomes the
Root bridge!
– Spanning Tree recalculates.
– The backbone from the original network is
now the backbone from the attacking host
to the other switches on the network.
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STP Attack Prevention
• Disabling STP can introduce
another attack.
• BPDU Guard
– Disables ports using portfast upon
detection of a BPDU message on
the port.
– Enabled on any ports running
portfast
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STP Attack Prevention
• Root Guard
– Prevents any ports that can become the
root bridge due to their BPDU
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CSM and CSM-S
• Cisco Content Switching Modules
• Cisco Content Switching Module with
SSL
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CDM
• Cisco Secure Desktop
– 3 major vulnerabilities
• Maintains information after an Internet
browsing session. This occurs after an SSL
VPN session ends.
• Evades the system via the system policies
preventing logoff, this will allow a VPN
connection to be activated.
• Allow local users to elevate their privileges.
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• Prevention
– Cisco has software to address the
vulnerabilities.
– There are workarounds available to mitigate
the effects of some of these vulnerabilities.
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Cisco Routers
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Cisco Routers
• Two potential issues with Cisco
Routers
– Problems with certain IOS software
– SNMP
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• Devices running Cisco IOS versions
12.0S, 12.2, 12.3 or 12.4
– Problem with the software
– Confidential information can be leaked out
– Software updates on the CISCO site can fix
this problem
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•Virtual Private Networks
Virtual connection 1
Virtual Connection 2
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•Virtual Private Networks
Error
Connection
Information leak
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• Cisco uBR10012 series devices automatically
enable SNMP read/write access
• Since there are no access restrictions on this
community string , attackers can exploit this to
gain complete control of the device
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CISCO
Router
Attacking
Computer
By sending an SNMP set request with a spoofed source IP address
the attacker will be able to get the Victim router to send him its
configuration file.
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CISCO
Router
With this information, the remote computer will be able to
have complete control over this router
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Attacking
Computer
• Fixes- Software updates available on
the CICSO site that will fix the
Read/Write problem
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Links
• http://sectools.org/tools2.html
• http://insecure.org/sploits/l0phtcrack.lanma
n.problems.html
• http://www.grc.com/intro.htm
• http://www.riskythinking.com
• http://www.hidemyass.com/
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References
• http://www.bmighty.com/network/showArticle.jhtml;jsessi
onid=2YYDWJHHX3FL2QSNDLPSKHSCJUNN2JVN?ar
ticleID=202401432&pgno=2
• http://www.juniper.net/security/auto/vulnerabilities/vuln19
998.html
• http://www.blackhat.com/presentations/bh-usa-02/bh-us02-convery-switches.pdf
• http://www.askapache.com/security/hacking-vlanTrishswitched-networks.html
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