University of WashingtonComputing & Communications Open Network Security or “closed network” insecurity? Terry Gray Director, Networks & Distributed Computing

University of Washington Computing & Communications

Open Network Security or “closed network” insecurity?

Terry GrayDirector, Networks & Distributed Computing

14 March 2002


UW Environment

• $1.5 B/yr enterpise (75% research/clinical)• 55,000 machines• Infinite variety and vintage of computers• Incredibly complex/diverse org structure• Relatively little centralized desktop mgt• Every dept’s middle name is Autonomous• C&C provides core I.T. infrastructure• Depts responsible for end-system support


Conventional Security Wisdom

• Popular Myth: “The network” caused the problem, so “the network” should solve it… So good security depends on:– border firewalls– border VPNs

• Unpopular Reality: In a large, diverse organization such as UW, security is not achieved by either one.


Unconventional Security Wisdom

“If you think technology can solve your security problems, then you don't understand the problems and you don't understand the technology. “

Bruce Schneier

Secrets and Lies


Gray’s Network Security Axioms

• Network security is maximized…when we assume there is no such thing.

• Firewalls are such a good idea…every host should have one. Seriously.

• Remote access is fraught with peril…just like local access.


Perimeter Protection Paradox

• Firewall “perceived value” is proportional to number of systems protected.

• Firewall effectiveness is inversely proportional to number of systems protected.

– Probability of compromised systems existing inside– Lowest-common-denominator blocking policy


Credo

• Open networks

• Closed servers

• Protected sessions


Security Elements• Architectural

– Authentication & Authorization – Encryption– Packet filtering

• Operational– Prevention– Detection– Recovery

• Policy– Risk Management– Liability Management


Start with a Security PolicyNow there’s an idea...

• Define who can/cannot do what to whom...

• Identify and prioritize threats

• Identify assumptions, e.g.– Security perimeters– Trusted systems and infrastructure– Hardware/software constraints

• Block threats or permit good apps?

• Minimize organizational distance between policy definition, configuration, and enforcement points


Network Risk Profile(notwithstanding recent SNMP exploits)


Heroic (but futile) Endeavors

• Getting anyone to focus on policies first

• Getting any consensus on border blocking

• Patching old end-systems

• Pretending that clients are only clients

• Securing access to older network gear


Bad Ideas

• Departmental firewalls within the core.

• VPNs only between institution borders.

• Over-reliance on large-perimeter defenses...e.g. believing firewalls can substitute for good host/application administration...


Good Ideas• Two-factor authentication• End-to-End encryption: IPSEC• End-to-End encryption: SSH/SSL/K5• Proactive vulnerability probing• Centralized desktop management service• Latest OS versions (w/integral firewalls)• Bulk email virus scanning• Server sanctuaries• Logical firewalls


Jury Still Out

• Intrusion Detection Systems

• DDoS trackers

• Thin Clients


When do VPNs make sense?

• E2E:– Whenever config cost is acceptably small

• Non-E2E:– When legacy apps cannot be accessed via

secure protocols, e.g. SSH, SSL, K5.and

– When the tunnel end-points are very near the end-systems.


Where do firewalls make sense?• Pervasively: (But of course we have a firewall…:)

– For blocking spoofed source addresses

• Small perimeter/edge:– Cluster firewalls, e.g. server sanctuaries, labs– OS-based and Personal firewalls

• Large perimeter/border:– Maybe to block an immediate attack?– Maybe if there is widespread consensus to block

certain ports? (Aye, and there’s the rub…)

– And then again, maybe not...


Fundamental Firewall Truths...

• Bad guys aren’t always "outside" the moat

• One person’s security perimeter is another’s broken network

• Organization boundaries and filtering requirements constantly change

• Perimeter defenses always have holes


The Dark Side of Border Firewalls It’s not just that they don’t solve the problem very well;

large-perimeter firewalls have serious unintended consequences

• Operational consequences– Force artificial mapping between biz and net perimeters– Catch 22: more port blocking -> more port 80 tunneling– Cost more than you think to manage; MTTR goes up– May inhibit legitimate activities– Are a performance bottleneck

• Organizational consequences– Give a false sense of security– Encourage backdoors– Separate policy configuration from best policy makers– Increase tensions between security, network, and sys admins


Mitnick’s Perspective

"It's naive to assume that just installing a firewall is going to protect you from all potential security threats. That assumption creates a false sense of security, and having a false sense of security is worse than having no security at all."

Kevin Mitnick

eWeek 28 Sep 00


Do You Feel Lucky?

• QUESTION: If a restrictive border firewall surrounds your --and 50,000 other-- computers, should you feel safe?

• ANSWER: Only if you regularly win the lottery!


Distributed Firewall Management• Given the credo of:

– Open networks– Closed servers– Protected sessions

• What about all the desktops?– Organizations that can tolerate a restrictive border

firewall usually centrally manage desktops

– Thus, they can also centrally configure policy-based packet filters on each desktop and don’t need to suffer the problems of border firewalls

– Centrally managing desktop firewalls possible even if desktops generally unmanaged


UW’s Logical Firewall• If edge and/or E2E protection isn’t possible, and the

idiots running the net “won’t help”…• Plugs into any network port• Departmentally managed• Opt-in deployment• Doesn’t interfere with network management• Uses Network Address Translation (NAT)• Intended for servers; can be used for clients• Web-based rules generator• Gibraltar Linux foundation


Server Sanctuaries

• Cluster sensitive/critical servers together…

• But don’t forget geographic-diversity needs

• Then provide additional logical and physical security


Technical Priorities

• Application security (e.g. SSH, SSL, K5)

• Host security (patches, minimum svcs)

• Strong authentication (e.g. SecureID)

• Net security (VPNs, firewalling)


Policy & Procedure• Policy definition & enforcement structure• Education/awareness: it’s everyone’s job• Standards and documentation• Adequate resources for system administration• High-level support for policies• Pro-active probing• Security consulting services• IDS and forensic services• Virus scanning measures• Acquiring/distributing tools, e.g. SSH


Risk & Liability Issues• Liability over network misuse?

– Policies define acceptable use– Post-audit strategy for enforcement– Wireless perimeter control?– Are networks an “attractive nuisance”?

• Risk of server compromise?– Strong preventive stance– Pre-audit via proactive probing– Greater sensitivity -> greater security


Reality Check

• John Gilmore: “The Internet deals with censorship as if it were a malfunction and routes around it”

• Isn’t this also true of other forms of policy-based restrictions, including Kazaa clamping and border port blocking?


“Inverted Networks”

• New trend in big companies (e.g. DuPont)

• Ditch the border firewall

• Assume LANs are “dirty”

• Use VPNs from each workstation to servers

• Hey, an open network, with closed servers and E2E encryption!

• Why didn’t we think of that? :)


Worrisome Trends

• Increasing sophistication of attacks

• Increasing number of attacks

• Tunneling everything thru port 80

• Partially connected Internets

• Increasing complexity anddiagnostic difficulty


Encouraging Trends

• Enterprise decision makers are engaged

• Vendors are paying more attention

• Software is slowly getting better

• ?


Conclusions• Central network services: think of as an ISP• Conventional wisdom won’t work in our world• Border firewalls can actually be harmful• We can’t afford to settle for fake security• There are no silver bullets• The hardest problems are non-technical• It’s still going to be a long, up-hill battle• Don’t forget disaster preparedness and recovery

(e.g. High-Availability system design)


Resources

• http://staff.washington.edu/gray/papers/credo.html

• http://staff.washington.edu/corey/fw/

• http://staff.washington.edu/dittrich

• http://www.sans.org/

Documents

University of WashingtonComputing & Communications Open Network Security or “closed network” insecurity? Terry Gray Director, Networks & Distributed Computing