EE579T/6GD #1 Summer 2003 © , Richard A. Stanley EE579T Network Security 6: Firewalls and Trusted Networks Prof. Richard A. Stanley

EE579T/6GD #2 Summer 2003 © , Richard A. Stanley Overview of Today’s Class Review last week’s lesson Security in the news Firewalls Trusted networks

EE579T/6GD #3 Summer 2003 © , Richard A. Stanley Summary TCP/IP was not intended as a secure protocol; as a result, it has vulnerabilities that can be exploited There are many ways to get access to info There are many types of attacks that can be mounted over network connections in order to gain unauthorized access to resources Never forget, the best access is hands-on

EE579T/6GD #4 Summer 2003 © , Richard A. Stanley Interesting Security Facts The average number of formidable Internet- based attacks currently are twice as likely to affect power utilities in the United States than financial firms Overall number of these attacks is growing “very rapidly” Data shows steady increase in attacks against electronic infrastructure Source: Securities Industry News

EE579T/6GD #5 Summer 2003 © , Richard A. Stanley More Statistics Most threats still from inside the firm Outside attacks still dominated by hackers Government or group sponsored attacks on the rise “...for the first time, empirical evidence has led to profiles of attacks that appear to be sponsored by governments or other organizations...” [Tim Belcher, CEO, Riptech] Source: Securities Industry News

EE579T/6GD #6 Summer 2003 © , Richard A. Stanley And more... Origin of attacks: –USA 30% –South Korea 9% –China 8% Based on number of Internet users, Israel leads the list as a source of attacks Beware jumping to conclusions--an attack from Country X may just be using their servers as a jumping-off point Source: Securities Industry News

EE579T/6GD #7 Summer 2003 © , Richard A. Stanley Outline Firewall Design Principles –Firewall Characteristics –Types of Firewalls –Firewall Configurations Trusted Systems –Data Access Control –The Concept of Trusted systems –Trojan Horse Defense

EE579T/6GD #8 Summer 2003 © , Richard A. Stanley Firewall is to Network as User privilege is to Operating system

EE579T/6GD #9 Summer 2003 © , Richard A. Stanley What Is a Firewall? A router with attitude? A device to implement an access control policy? A physical device? A logical device? The preferred solution for network protection?

EE579T/6GD #10 Summer 2003 © , Richard A. Stanley Firewalls Effective means of protection a local system or network of systems from network-based security threats while affording access to the outside world via WAN`s or the Internet Despite common opinion, not a panacea or an “out-of-the-box” security solution

EE579T/6GD #11 Summer 2003 © , Richard A. Stanley Where Does This Term Come From? Firewall means a fire separation of noncombustible construction that subdivides a building or separates adjoining buildings to resist the spread of fire that has a fire-resistance rating as prescribed in the Building Code and that has structural stability to remain intact under fire conditions for the required fire-rated time. Source: The Ontario Fire Code, §

EE579T/6GD #12 Summer 2003 © , Richard A. Stanley Firewall Design Principles Information systems undergo a steady evolution (from small LAN`s to Internet connectivity) Strong security features for all workstations and servers not established

EE579T/6GD #13 Summer 2003 © , Richard A. Stanley Firewall Design Principles The firewall is inserted between the premises network and the Internet or another external network Aims: –Establish a controlled link –Protect the premises network from Internet- based or “outside” attacks –Provide a single choke point (good or bad?)

EE579T/6GD #14 Summer 2003 © , Richard A. Stanley Firewall Characteristics Design goals: –All traffic from inside to outside must pass through the firewall (physically blocking all access to the local network except via the firewall) –Only authorized traffic (defined by the local security policy) will be allowed to pass

EE579T/6GD #15 Summer 2003 © , Richard A. Stanley Firewall Characteristics Design goals: –The firewall itself is immune to penetration (use of trusted system with a secure operating system) –Although this is a noble goal, it is virtually impossible to achieve!

EE579T/6GD #16 Summer 2003 © , Richard A. Stanley Firewall Characteristics - 1 Service control –Determines the types of external services that can be accessed, inbound or outbound Direction control –Determines the direction in which particular service requests are allowed to flow

EE579T/6GD #17 Summer 2003 © , Richard A. Stanley Firewall Characteristics - 2 User control –Controls access to a service according to which user is attempting to access it Behavior control –Controls how particular services can be used (e.g. filter )

EE579T/6GD #18 Summer 2003 © , Richard A. Stanley Types of Firewalls Three common types of Firewalls: –Packet-filtering routers –Application-level gateways –Circuit-level gateways

EE579T/6GD #19 Summer 2003 © , Richard A. Stanley Types of Firewalls Packet-filtering Router

EE579T/6GD #20 Summer 2003 © , Richard A. Stanley Packet-Filtering Firewall Applies a set of rules to each incoming IP packet and then forwards or discards the packet Filters packets going in both directions The packet filter is typically set up as a list of rules based on matches to fields in the IP or TCP header Two default policies (discard or forward)

EE579T/6GD #21 Summer 2003 © , Richard A. Stanley Packet Filtering Firewall Advantages: –Simplicity –Transparency to users –High speed Disadvantages: –Difficult to set up packet filter rules –Lack of authentication

EE579T/6GD #22 Summer 2003 © , Richard A. Stanley Packet Filtering Firewall Possible attacks and appropriate countermeasures –IP address spoofing –Source routing attacks –Tiny fragment attacks

EE579T/6GD #23 Summer 2003 © , Richard A. Stanley Types of Firewalls Application-level Gateway

EE579T/6GD #24 Summer 2003 © , Richard A. Stanley Application-level Gateway Also called proxy server Acts as a relay of application-level traffic

EE579T/6GD #25 Summer 2003 © , Richard A. Stanley Application-level Gateway Advantages: –Higher security than packet filters –Only need to scrutinize a few allowable applications –Easy to log and audit all incoming traffic Disadvantages: –Additional processing overhead on each connection (gateway as splice point) –Speed

EE579T/6GD #26 Summer 2003 © , Richard A. Stanley Types of Firewalls Circuit-level Gateway

EE579T/6GD #27 Summer 2003 © , Richard A. Stanley Circuit-level Gateway Stand-alone system, or Specialized function performed by an application-level gateway Sets up two TCP connections The gateway typically relays TCP segments from one connection to the other without examining the contents

EE579T/6GD #28 Summer 2003 © , Richard A. Stanley Circuit-level Gateway Security function consists of determining which connections will be allowed Typically used where the system administrator trusts the internal users An example is the SOCKS package

EE579T/6GD #29 Summer 2003 © , Richard A. Stanley Types of Firewalls Bastion Host –Sometimes called a DMZ –A system identified by the firewall administrator as a critical strong point in the network´s security –The bastion host serves as a platform for an application-level or circuit-level gateway

EE579T/6GD #30 Summer 2003 © , Richard A. Stanley Firewall Configurations In addition to using simple configuration of a single system (single packet filtering router or single gateway), more complex configurations are possible Three common configurations

EE579T/6GD #31 Summer 2003 © , Richard A. Stanley Firewall Configurations Screened host firewall system (single- homed bastion host)

EE579T/6GD #32 Summer 2003 © , Richard A. Stanley Screened Host Firewall Firewall consists of two systems: –A packet-filtering router –A bastion host Configuration for the packet-filtering router: –Only packets from and to the bastion host are allowed to pass through the router The bastion host performs authentication and proxy functions

EE579T/6GD #33 Summer 2003 © , Richard A. Stanley Screened Host Firewall Greater security than single configurations : –Implements both packet-level and application- level filtering (allowing for flexibility in defining security policy) –An intruder must generally penetrate two separate systems (but if outside router compromised, what then?) Affords flexibility in providing direct Internet access (public information server, e.g. Web server)

EE579T/6GD #34 Summer 2003 © , Richard A. Stanley Firewall Configurations Screened host firewall system (dual-homed bastion host)

EE579T/6GD #35 Summer 2003 © , Richard A. Stanley Dual-homed Bastion Host Even if the packet-filtering router is completely compromised –Traffic between the Internet and other hosts on the private network has to flow through the bastion host –Provides two layers of security

EE579T/6GD #36 Summer 2003 © , Richard A. Stanley Firewall Configurations Screened-subnet firewall system

EE579T/6GD #37 Summer 2003 © , Richard A. Stanley Screened-Subnet Firewall Most secure configuration of the three Two packet-filtering routers are used –One between bastion host and external network –One between bastion host and internal network Creates an isolated sub-network

EE579T/6GD #38 Summer 2003 © , Richard A. Stanley Screened-Subnet Firewall Advantages: –Three levels of defense to thwart intruders –Outside router advertises only the existence of the screened subnet to the Internet (internal network is invisible to the Internet) –Inside router advertises only the existence of the screened subnet to the internal network (systems on the inside network cannot construct direct routes to the Internet)

EE579T/6GD #39 Summer 2003 © , Richard A. Stanley Firewalls Useful to enforce security policy at the network edges Popularly believed to provide “hardened” security as they come out of the box If not properly configured, can introduce more problems than they solve Come in both hardware and software flavors, but all have software inside

EE579T/6GD #40 Summer 2003 © , Richard A. Stanley Trusted Systems One way to enhance the ability of a system to defend against intruders and malicious programs is to implement trusted system technology Be careful whom you trust!

EE579T/6GD #41 Summer 2003 © , Richard A. Stanley Data Access Control Through the user access control procedure (log on), user is identified to the system Associated with each user, there is a profile that specifies permissible operations and file accesses The operating system can enforce rules based on the user profile –This is why Win9x cannot be used here

EE579T/6GD #42 Summer 2003 © , Richard A. Stanley Data Access Control General models of access control: –Access matrix –Access control list –Capability list We saw all these in Computer Security, in the implementation of security models like Bell-LaPadula

EE579T/6GD #43 Summer 2003 © , Richard A. Stanley Data Access Control Access Matrix

EE579T/6GD #44 Summer 2003 © , Richard A. Stanley Data Access Control Access Matrix: Basic elements of the model –Subject: An entity capable of accessing objects, the concept of subject equates with that of process –Object: Anything to which access is controlled (e.g. files, programs) –Access right: The way in which an object is accessed by a subject (e.g. read, write, execute)

EE579T/6GD #45 Summer 2003 © , Richard A. Stanley Data Access Control Access Control List: Decomposition of the matrix by columns

EE579T/6GD #46 Summer 2003 © , Richard A. Stanley Data Access Control Access Control List –An access control list lists users and their permitted access right –The list may contain a default or public entry –This is how Unix handles security, and is the only mechanism available in Unix Everything in Unix looks like a text file All files have 9-bit permissions in the inode pointer

EE579T/6GD #47 Summer 2003 © , Richard A. Stanley Data Access Control Capability list: Decomposition of the matrix by rows

EE579T/6GD #48 Summer 2003 © , Richard A. Stanley Data Access Control Capability list –A capability ticket specifies authorized objects and operations for a user –Each user has a number of tickets

EE579T/6GD #49 Summer 2003 © , Richard A. Stanley Trusted Systems Concept Trusted Systems –Protect data and resources on the basis of levels of security (e.g. military) –Users can be granted clearances to access certain categories of data –Trusted systems need not discern levels of permissions; they can operate “system high” cf. Telephone systems

EE579T/6GD #50 Summer 2003 © , Richard A. Stanley Security Levels Multilevel security: multiple categories or levels of data Multilevel secure system must enforce: –No read up: A subject can only read an object of lower or equal security level (BLP Simple Security Property) –No write down: A subject can only write into an object of greater or equal security level (BLP *-Property) –May enforce discretionary security (BLP DS property) Security levels may be linear or latticed

EE579T/6GD #51 Summer 2003 © , Richard A. Stanley Trusted Systems Implementation Reference Monitor provides multilevel security for a data processing system –Reference Monitor is a concept, not a thing

EE579T/6GD #52 Summer 2003 © , Richard A. Stanley Reference Monitor Up Close and Personal

EE579T/6GD #53 Summer 2003 © , Richard A. Stanley Reference Monitor Controlling element in the security kernel of a computer that regulates access of subjects to objects on basis of security parameters The monitor has access to a file (security kernel database) The monitor enforces the security rules (no read up, no write down)

EE579T/6GD #54 Summer 2003 © , Richard A. Stanley Reference Monitor Properties Complete mediation: Security rules are enforced on every access Isolation: Reference monitor and database protected from unauthorized modification Verifiability: reference monitor’s correctness must be mathematically provable –this may be where we bend the rules!

EE579T/6GD #55 Summer 2003 © , Richard A. Stanley Trusted Systems A system that can provide such verifications (properties) is referred to as a trusted system

EE579T/6GD #56 Summer 2003 © , Richard A. Stanley Trojan Horse Defense Secure, trusted operating systems are one way to secure against Trojan Horse attacks

EE579T/6GD #57 Summer 2003 © , Richard A. Stanley Trojan Horse Defense

EE579T/6GD #58 Summer 2003 © , Richard A. Stanley Trojan Horse Defense

EE579T/6GD #59 Summer 2003 © , Richard A. Stanley Summary Firewalls are useful tools to mediate access from internal networks to external networks Firewalls are not a single-point security solution Firewalls cannot protect against a malicious user on the internal network Trusted computing systems are needed to enforce security policy

EE579T/6GD #60 Summer 2003 © , Richard A. Stanley Homework Read text, Chapters 11 and 8 Choose a firewall product, and describe in detail how you would implement the following security policy: –Anyone on the inside network may establish any connection they desire from outside –No one on the outside network may initiate a connection to the inside –Outsiders may not ping in, but insiders can ping out