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Network Security Issues

Pete Siemsensiemsen@ucar.edu

National Center for Atmospheric Research

April 24th, 2002

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Obstacles to Security• Doesn’t mesh well with research• Security is a lose-lose proposition!

• Too little security: it’s your fault· We got hacked, you should’ve done more

• Too much security: it’s your fault· I can’t get my work done, you should do less

• And when it works, no one notices• Considered low priority (few resources)• Security not always taken seriously

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Types of Threats• Viruses• Packet sniffing• Denial of service• Probing for holes• Wireless

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Viruses• Hard to battle• Mail-borne• Web-borne• Filtering

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Packet Sniffing• Switches are better than hubs• Try to reduce cleartext passwords on

the net: ban telnet in favor of ssh

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Denial of Service• Usually short-lived• Must back-track to source, installing

filters as you go• Distributed DoS can’t be blocked• No magic bullet

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Probing for holes• “script kiddies” are unsophisticated

hackers who run software “kits” to attack a target. They don’t have to understand networking.

• Software scans for open ports and known vulnerabilities

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Wireless security• Built-in WEP is insecure• Your wireless net may be wide open to

anyone• Details at http://www.scd.ucar.edu

/nets/projects/wireless/

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Case study: NCAR

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NCAR’s Environment• Academic research institution

• But no students• Collaboration with 63 member Universities

• ~1500 university (external) users• Diverse, widespread field projects• ~2500 networked nodes internal to NCAR

• ~1500 internal users

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NCAR’s Motivation to Get Serious About Security

• We experienced increasing malicious attacks• More hackers hacking• Availability of script kiddie “kits”

· Easy to get· Don’t require network expertise

• We had some strong advocates

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Getting Started

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NCAR Security Committee

• We created a committee to develop policy• Sysadmins from all NCAR Divisions• Policy process delivers institutional buy-in• 2-hour meetings once a month• Lots of cooperation, little authority• With time, authority has grown

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The Security Policy• Need a policy that defines

• vulnerabilities• how much security is needed• level of inconvenience that is tolerable• solutions

• We recommended a full-time Security Administrator for the institution

• http://www.ncar.ucar.edu/csac

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Define Scope of Problem• Decide which types of attacks are problems• Examples:

• Hacker spoofing of source IP address • Hacker scanning for weaknesses

· TCP/UDP ports, INETD services • Hackers sniffing passwords• Hacker exploitation of buggy operating systems

· Inconsistent/tardy OS patching

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Define Scope of Solution• What we won’t do

• Not feasible to secure every computer• Over-reliance on timely OS security fixes• Can’t prohibit internal “personal” modems• Attacks from within aren’t a big problem

• What we will do• Reduce external attacks from the Internet

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Basic Solutions at NCAR

• One-time passwords• Switched LANs• Router packet filtering• Application-proxy gateways• Filter email attachments

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One-time Passwords• A.K.A. Challenge-Response• Requires little calculator things (~$50/per)• Prevents password sniffing• We use it on critical devices

• Routers, ATM Switches, Ethernet Switches, Remote Access Servers, Server hosts (root accounts)

• At the least, do this!

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Switched LANs

• Reduces packet eavesdropping• Get this for “free” with switched network• Can still steal ARP entries

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Packet Filtering

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Router-Based Filters• Used to construct router-based firewall

around your internal network• Main security implementation tool• Routers check each inbound packet

against filter criteria and accept or reject• Filters reject dangerous packets• Filters accept all useful packets

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Packet Filtering At NCAR• Cisco access-lists filter on

• IP address source, destination, ranges• Interfaces: inbound and/or outbound• Protocols, TCP ports, etc.

• We filter inbound and outbound packets• Performance can be an issue

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Filter Stance: Strong or Weak?

• Strong• Deny everything, except for the good stuff

• Weak• Allow everything, except for the bad stuff

• NCAR chose a Strong stance

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Example Filter Statistics• 41 lines (rules) in NCAR’s access-list• Hits as of 9/30/98, 28 days after filter

was installed:• 3 MP Denied because of spoofing• 17 MP Denied because of “catchall”• 71 MP Permitted to exposed networks• 100MP Permitted to exposed hosts

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Exposed Hosts

• Example: Web servers, data source machines, etc.

• Must meet stringent security standards to avoid being compromised and used as launch pads for attacking protected hosts• OS restricts set of network services allowed• Must keep up with OS patches

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Security Administrator• Provides focus for security for the entire

institution• Helps deal with break-ins

• Central point of contact• Tracks CERT advisories for sysadmins• Advocates security solutions, like ssh• Scans exposed hosts for standards violations• Generally helps/educates sysadmins

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Impacts of NCAR’s Security

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Benefits

• >99% of NCAR hosts are protected• Outbound Telnet, HTTP, etc. still work• Relatively cheap and easy• Dial-in users are “inside”, no changes

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Drawbacks• UDP is blocked• Some services are no longer available

• Inbound pings are blocked !!!• To use FTP, must use passive mode, or

use an exposed host, or proxy through the Gateway

• DNS and email can get complicated

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Drawbacks (cont.)

• Crunchy outside, chewy inside• Modems in offices are a huge hole• Users must install VPN or ssh

software for remote access

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Wrapup

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Security is Never “Done”

• How do you know if you’re being hacked?• “Silent” attacks very hard to detect• “Noisy” attacks hard to distinguish from

other network (or host) problems• Network keeps changing• Software keeps changing• Hackers keep advancing

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Security is Never “Done” (cont.)

• Policy and security mechanisms must evolve

• Security committee continues to meet

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Conclusion

• NCAR struck a balance between:• Convenience and Security• Politics and Technology• Cost and Quality