Investigations into BIND Dynamic Update with OpenSSL by David Wilkinson

Overview of DDOS attack DNS... Victim A = Agent R = Router AAAAAAAA compromised.netvigilant.netincompetent.net DNS... R R reflecting networks R R R R R R R

Stopping attack with the Secure Collective Defense (SCOD) DNS... Victim A = Agent R = Router AAAAAAAA compromised.netvigilant.netincompetent.net DNS... R R reflecting networks R R RR R R proxy blocked blocked by IDS blocked reroute “Could I get some help here?”

This project: focus on sending the reroute message to the servers of authority (soa) of preferred clientele Potential roadblocks/snafus: –How to authenticate machine sending the reroute command to the various DNS servers, and visa versa? –How to change DNS software to accept this new command and reroute clients accordingly?

Using OpenSSL for Authentication BIND9’s transaction signatures (TSIG) use shared keys for verification; not practical for verifying any machine on Internet BIND9’S DNS Security Extensions (DNSSEC) utilize public key cryptography to allow the client to authenticate the server, but not the other way around A secure socket layer (SSL) on the other hand, enables any client and server on the Internet to verify the legitimacy of each other using public key cryptography. Use OpenSSL here because it’s free.

Combine OpenSSL with a modified version of ‘nsupdate’ to create ‘reroute’ In BIND9, the nsupdate command allows an authorized machine to change the zone data in a DNS server Mostly used by ISPs and large companies to assign IP addresses to dialup and cable modem customers dynamically ex: #nsupdate >prereq nxdomain mib.fx.movie.edu. >update add mib.fx.movie.edu. 300 A > result: host mib.fx.movie.edu with IP address is added to server’s zone file!

reroute is different from nsupdate in the following ways: reroute does not update the zone data for its own network’s (i.e., the victim’s) server of authority (soa). Instead it needs to add a new temporary zone file (that maps the victim host to the IP address of a proxy server in the SCOD schema) in the soa of every preferred client it has in its database. Dynamic updates cannot add new zones, period. (Or, in an alternate solution, reroute may add the preferred clients to a new ‘view’ in the victim’s DNS server. This view maps the victim host to the IP address of a proxy server. nsupdate cannot add new views nor add clients to the view list. However, during a DDOS attack, the victim’s DNS server may become unavailable, so the first option may be preferable.) Mutual authentication between server and client with SSL

Progress on adding SSL to nsupdate Learned how to configure OpenSSL to create a certificate for a trusted root CA. Changed configuration file to create client and server certs signed by this CA. Set up a simple client and server that authenticated each other and communicated through an encrypted channel. Traced the flow of nsupdate with GDB with the TCP option (-v) set. nsupdate.c and request.c must be modified on client (i.e., nsupdate) side; interfacemgr.c and client.c must be modified on server (i.e., named) side. Adding code to client side not without trials and tribulations; not enough time for server side.

Work Ahead Get nsupdate and named to actually authenticate each other Make new command, reroute, from nsupdate that adds temp. zone files to foreign DNS servers or, alternatively, adds a new view to the victim DNS server with a match-list of preferred customers. This view routes the clients to the victim through proxy servers.

References DNS and BIND. Paul Albitz and Cricket Liu, O’Reilly & Associates, Inc., Network Security with OpenSSL. John Viega, Matt Messier & Pravir Chandra, O’Reilly, “The ‘stacheldraht’ distributed denial of service attack tool.” David Dittrich, University of Washington, Dec. 31, “DRDoS: Distributed Reflection Denial of Service.” Steve Gibson, grc.com, Feb. 22, 2002.