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Network Security Issues. Pete Siemsen siemsen@ucar.edu National Center for Atmospheric Research April 24 th , 2002. 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
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Network Security Issues Pete Siemsen siemsen@ucar.edu National Center for Atmospheric Research April 24th, 2002
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
Types of Threats • Viruses • Packet sniffing • Denial of service • Probing for holes • Wireless
Viruses • Hard to battle • Mail-borne • Web-borne • Filtering
Packet Sniffing • Switches are better than hubs • Try to reduce cleartext passwords on the net: ban telnet in favor of ssh
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
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
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/
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
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
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
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
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
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
Basic Solutions at NCAR • One-time passwords • Switched LANs • Router packet filtering • Application-proxy gateways • Filter email attachments
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! One-time Passwords
Switched LANs • Reduces packet eavesdropping • Get this for “free” with switched network • Can still steal ARP entries
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 Router-Based Filters
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 Packet Filtering At NCAR
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
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
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 Exposed Hosts
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 Security Administrator
>99% of NCAR hosts are protected Outbound Telnet, HTTP, etc. still work Relatively cheap and easy Dial-in users are “inside”, no changes Benefits
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 Drawbacks
Crunchy outside, chewy inside Modems in offices are a huge hole Users must install VPN or ssh software for remote access Drawbacks (cont.)
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
Security is Never “Done” (cont.) • Policy and security mechanisms must evolve • Security committee continues to meet
Conclusion • NCAR struck a balance between: • Convenience and Security • Politics and Technology • Cost and Quality