Firewalls and application gateways Intrusion Detection Systems Honeypots
PA197 Secure Network Design Network Defense Mechanisms
Eva Hladká, Luděk Matýska Faculty of Informatics 26 April 2023
Eva Hladká, Luděk Matýska
PA197 Secure Network Design Network Defense Mechanisms
Firewalls and application gateways Intrusion Detection Systems Honeypots
Firewalls and application gateways
• Firewalls
• Packet Filters
9 Stateful Firewalls
• Application gateways
• Personal firewalls
Intrusion Detection Systems o IDS for Mobile Networks
Honeypots
Eva Hladká, Luděk Matýska
PA197 Secure Network Design Network Defense Mechanisms
Firewalls and application gateways Intrusion Detection Systems Honeypots
Firewalls Packet Filters Stateful Firewalls Application gateways Personal firewalls
Concept of inside and outside of a network
• different trust levels
o different security levels
• access control is on the boundary (perimeter) Firewall as the boundary keep
• makes decisions to allow or deny passage of packets according to a specified policy
• demilitarized zone (DMZ) o reference monitor
o unbypassable, tamperproof, analyzable (logs)
• defines security perimeter
• access control/security imposed
• exposure limit
• partitions the network (security domains)
Eva Hladká, Luděk Matýska
PA197 Secure Network Design Network Defense Mechanisms
Firewalls and application gateways Intrusion Detection Systems Honeypots
Firewalls Packet Filters Stateful Firewalls Application gateways Personal firewalls
• Firewall enforces a policy
• administrative boundaries
what kind of data to block/pass?
• Philosophies
• default: allow or deny?
• inbound or outbound traffic
• symmetric or asymmetric (same/different rules for in/out bound traffic)
• Rules
• generation: manual versus automatic (learning)
• simple or complex rules?
Eva Hladká, Luděk Matýska
PA197 Secure Network Design Network Defense Mechanisms
Firewalls and application gateways Intrusion Detection Systems Honeypots
Firewalls Packet Filters Stateful Firewalls Application gateways Personal firewalls
• Design goals
• all traffic between "inside" (network behind the firewa "outside" network must go through the firewall
• only authorized traffic is allowed to pass
• security/access policy
• firewall itself is tamperproof
• use of trusted system
• secure operating system
II) and
Eva Hladká, Luděk Matýska
PA197 Secure Network Design Network Defense Mechanisms
Firewalls and application gateways Intrusion Detection Systems Honeypots
Firewalls Packet Filters Stateful Firewalls Application gateways Personal firewalls
General techniques 9 service control
• what can be accessed
• user control
• who can use a particular service
• behaviour control
• how the service is used
• direction control
• inbound and outbound traffic treated differently
Eva Hladká, Luděk Matýska
PA197 Secure Network Design Network Defense Mechanisms
Firewalls and application gateways Intrusion Detection Systems Honeypots
Firewalls Packet Filters Stateful Firewalls Application gateways Personal firewalls
9 Packet filters
• first generation operate at the IP layer
• Stateful inspection
• second generation
o also called circuit-level firewalls
• operate at the transport layer
• Application layer
• third generation
• also called application gateway
• higher layers, it can "understand" the traffic
• NAT
• only partially belongs here
• hides internal network
• protects against network reconnaissance
Eva Hladká, Luděk Matýska
PA197 Secure Network Design Network Defense Mechanisms
Firewalls and application gateways Intrusion Detection Systems Honeypots
Firewalls Packet Filters Stateful Firewalls Application gateways Personal firewalls
• Basic properties
• list of rules to apply
• IP addresses, ports, protocols, flags, interfaces
• usually using data from IP (or TCP) header
• not strictly layer 3 only
• Stateless
applies set of rules to each incoming packet
• forwards or discards it
• Uni-directional
• each direction is treated independently
• High throughput
Eva Hladká, Luděk Matýska
PA197 Secure Network Design Network Defense Mechanisms
Firewalls and application gateways Intrusion Detection Systems Honeypots
Firewalls Packet Filters Stateful Firewalls Application gateways Personal firewalls
• Tracks state information of connections
• maintains table of active connections
• passively monitors them
9 Context sensitive
• context established by preceding packets
• dynamic change of filtering rules
o Expensive setup, cheap processing
• inclusion of a session (TCP, UDP) into the table
• cheap processing of packets within a session
o UDP and ICMP problems
9 not truly stateful protocols
• end of session only through timeout
Eva Hladká, Luděk Matýska
PA197 Secure Network Design Network Defense Mechanisms
Firewalls and application gateways Intrusion Detection Systems Honeypots
Firewalls Packet Filters Stateful Firewalls Application gateways Personal firewalls
• Linux application to configure Linux kernel firewall
• Different modules:
o iptables for IPv4
• ip6tables for IPv6
• arptables for ARP
• ebtables for Ethernet frames
Gradually replaced by nftables
o Features:
• packet filtering
• connection tracking (stateful)
• NAT
q rate limiting
• logging
Eva Hladká, Luděk Matýska
PA197 Secure Network Design Network Defense Mechanisms
Firewalls and application gateways Intrusion Detection Systems Honeypots
Firewalls Packet Filters Stateful Firewalls Application gateways Personal firewalls
Project to provide packet filtering and classification for Linux
• Linux kernel engine: a virtual machine optimized for network packet inspection controlled through a bytecode; also atomic rule replacement API
• user space utility: translates rules into bytecode
• Command line tool: nft
o Examples of simple rules
• Drop TCP traffic for port 22
• nft add rule filter forward tcp dport 22 drop
• nft add rule filter2 input tcp dport { telnet, http, https } accept
Eva Hladká, Luděk Matýska
PA197 Secure Network Design Network Defense Mechanisms
Firewalls and application gateways Intrusion Detection Systems Honeypots
Firewalls Packet Filters Stateful Firewalls Application gateways Personal firewalls
table firewall { chain incoming { type filter hook input priority 0;
# accept established and related connections
ct state etsablished, related accept
# accept loopback interface traffic
iifname lo accept
# accept icmp
icmp type echo-request accept
# open sshd (22) and httpd (80) tcp ports
tcp dport {ssh, http} accept
# reject everything else
drop
}
i_
Eva Hladká, Luděk Matýska
PA197 Secure Network Design Network Defense Mechanisms
Firewalls and application gateways Intrusion Detection Systems Honeypots
Firewalls Packet Filters Stateful Firewalls Application gateways Personal firewalls
• Proxy (application gateway)
• the firewalls serves/looks as a proxy
• all traffic goes through it (relay at the application layer)
• decisions customized to the application
• application context
• examples: e-mail or web filter
• Deep packet inspection
• beyond stateful inspection
• deep knowledge of application payload
• Challenges
• performance (induced latency)
• complexity
breaks end-to-end principle—secure connections
Eva Hladká, Luděk Matýska
PA197 Secure Network Design Network Defense Mechanisms
• The original idea of secure perimeter is becoming obsolete
• too many intentional holes in firewalls
• VPNs, VLAN extensions encrypted traffic
• Insiders' threats
• 60-80% attacks go from inside the network
• The "demilitarized zone" pushed to a single machine
• each machine protected independently
• highly adaptive (to full programs)
• excellent context
• performance impact
Eva Hladká, Luděk Matýska
PA197 Secure Network Design Network Defense Mechanisms
Firewalls and application gateways Intrusion Detection Systems Honeypots
Firewalls Packet Filters Stateful Firewalls Application gateways Personal firewalls
An environment with machines/systems deliberately exposed to the external network
Allows to provide service to external subjects Also behind the firewall
• all traffic between DMZ and internal network as well as between DMZ and external network goes through the firewall
Single firewall solution
• three lines from a firewall
• to the external world
• to the internal network
• to the DMZ
Two firewalls solution
• the first firewall stands between the DMZ and the external world
• the second firewall stands between the DMZ and internal network
Eva Hladká, Luděk Matýska
PA197 Secure Network Design Network Defense Mechanisms
• Bugs and errors
• software bugs and misconfigurations occur
• Perimeter redefinition
• WiFi and mobile devices
• external partners with need to access internal network
• BYOD policy
• Perimeter extension through VPN
• weak control of the other side
• Insider threats
• majority of attacks from inside
• weakening the perimeter does not help
• social engineering, phishing, allowed services exploits
Eva Hladká, Luděk Matýska
PA197 Secure Network Design Network Defense Mechanisms
Firewalls and application gateways Intrusion Detection Systems Honeypots
• We should accept that no protection is perfect
• the attacker will get in!
9 Intrusion Detection Systems
• monitor network activity
• look for sign of intrusion/intrusion attempts
• detect and then react
• Where to monitor
• Network IDS
• like an application gateway
• Host IDS
• like a personal firewall
Eva Hladká, Luděk Matýska
PA197 Secure Network Design Network Defense Mechanisms
Firewalls and application gateways Intrusion Detection Systems Honeypots
<* Monitors network for malicious or suspicious events
• network tap
• span port
• software in promiscuous mode (tcpdump)
• deployed across the (local area) network
• Advantages
• low cost
• transparent to users (and adversary)
• isolation
• visibility across network
• recognizes gradual attack
• Problems
• encryption
o evasion techniques
• not able to detect "normal" modes
Eva Hladká, Luděk Matýska
PA197 Secure Network Design Network Defense Mechanisms
Firewalls and application gateways Intrusion Detection Systems Honeypots
• IDS raises an alert if an anomaly is found
• Accuracy is of critical importance
o Correct modes:
• True positive
• a true attack is correctly recognized
• True negative
• an anomaly is correctly detected as "no attack"
• Incorrect modes
• False positive
• reports an attack that does not exist
• False negative
• attack goes unrecognized (no alert)
Eva Hladká, Luděk Matýska
PA197 Secure Network Design Network Defense Mechanisms
Firewalls and application gateways Intrusion Detection Systems Honeypots
• Looking for anomalies
9 unexpected behaviour taken as evidence of intrusion
• needs a model of "normal" behaviour
• thresholds/statistical modeling/Markov-based (state)
• statistical anomaly-based <* Used metrics
• traffic extent, connection attempts, payload byte distribution, flows
selected features should characterize expected behaviour
• Advantages
• broad coverage (learning; able to detect previously unknown attacks)
• not easy to evade
• Disadvantages
• need training, false positives (alerts), legitimate changes in behaviour
Eva Hladká, Luděk Matýska
PA197 Secure Network Design Network Defense Mechanisms
Firewalls and application gateways Intrusion Detection Systems Honeypots
• Direct search for known bad behaviour
• Signature-based
• rule-based detection
• signatures; states, pattern-matching
• activity patterns matching known attack or policy violation
Database of signatures
• Advantages
• lower false positive rate
• could include specific alerts
• Disadvantages
• narrow (only known attacks)
• evasion prone
• need constant updates (external source)
Eva Hladká, Luděk Matýska
PA197 Secure Network Design Network Defense Mechanisms
Firewalls and application gateways Intrusion Detection Systems Honeypots	IDS for Mobile Networks
Snort	
• Widely used open source NIDS
• signature based
• Features
• protocol analysis
• content searching/matching
9 Attack detection
• buffer overflows
• stealth port scans
• CGI attacks
• SMB probes
• OS fingerprinting etc.
» Available at http: //www. snort. org
Eva Hladká, Luděk Matýska PA197 Secure Network Design Network Defense Mechanisms
Firewalls and application gateways Intrusion Detection Systems Honeypots
• Use case will be provided based on the following articles:
• Y. Zhang, W. Lee, Y-A. Huang (2003): Intrusion Detection techniques for Mobile Wireless Networks.
• P.M. Mafra, J.S. Fraga, A.O. Santin (2014): Algorithms for a distributed IDS in MANETs. J. Comp. Syst. Sciences,
VOI 80(1), pp. 554-570.
Eva Hladká, Luděk Matýska
PA197 Secure Network Design Network Defense Mechanisms
Firewalls and application gateways Intrusion Detection Systems Honeypots
• Using deception as a defense
• diverting attack to a secure site
• consuming attacker's resources
o forcing them to reveal their techniques/goal
<* Pretends to be the attacker's target
• Allows to study vulnerabilities and what adversary does after gaining control
• Hig/Low interaction honeypots
Eva Hladká, Luděk Matýska
PA197 Secure Network Design Network Defense Mechanisms
Firewalls and application gateways Intrusion Detection Systems Honeypots
• Real (full) systems and services
• Allow full compromise of the target system
• Mostly virtual systems
9 easily to replace/manage
a Challenges
• maintenance, scaling
• risk of further attacks (originating from honeypot)
• intrusion detection (e.g. dynamic taint analysis)
• Output
• attack footprint (registers, memory, applications, . ..)
Eva Hladká, Luděk Matýska PA197 Secure Network Design Network Defense Mechanisms
Firewalls and application gateways Intrusion Detection Systems Honeypots
• Just emulate aspects of real system
• limited interaction
• statistics collection
• Advantages
• simplicity, maintenance
• easy installation
• low risk (no attack originating from honeypot) o Outputs similar to high interaction honeypots
Eva Hladká, Luděk Matýska
PA197 Secure Network Design Network Defense Mechanisms
Firewalls and application gateways Intrusion Detection Systems Honeypots
9 Definition of a perimeter and internal and external network o Putting firewall at the perimeter
• able to detect and stop open attacks
• weak against current perimeter diffusion
• majority of attacks from inside
• Continuous monitoring through IDS
• could reveal attacks regardless of origin
• adaptable to new threats
• improper setup could be dangers (e.g. too many false positives)
• Next lecture: More extensive traffic monitoring
Eva Hladká, Luděk Matýska
PA197 Secure Network Design Network Defense Mechanisms