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Poll load to compute return list

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Unformatted text preview: r name server –  Guessing has 1 in 65535 chance (Or does it?) •  Now: –  Ask the local server to lookup google.com –  Spoof the response from google.com using the correct ID –  Bogus response arrives before legit one (maybe) •  Local server caches first response it receives –  ATacker can set a long TTL Guessing Query ID hTp://www.unixwiz.net/tech)ps/iguide- kaminsky- dns- vuln.html Cache Poisoning hTp://www.unixwiz.net/tech)ps/iguide- kaminsky- dns- vuln.html Hijacking Authority Record hTp://www.unixwiz.net/tech)ps/iguide- kaminsky- dns- vuln.html Kaminsky Exploit •  If good guy wins the race, you have to wait un)l the TTL to race again •  But… –  What if you start a new race, for AAAA.google.com, AAAB.google.com, …? –  Forge CNAME responses for each –  Circumvents bailiwick checking Countermeasures •  Randomize id –  Used to be sequen)al •  Randomize source port number –  Used to be the same for all requests from the server •  Offers some protec)on, but aTack s)ll possible Load Balancing using DNS •  Return mul)ple IP addresses (“A” records) for a name •  Benefits –  Spread the load evenly across the IP addresses •  Problems –  Caching, no standard on which address to use, … •  How to solve these problems? –  Poll load to compute return list –  hTp://en.wikipedia.org/wiki/Round- robin_DNS dig www.google.com! ! ; <<>> DiG 9.7.3-P3 <<>> www.google.com! ;; global options: +cmd! ;; Got answer:! ;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 9457! ;; flags: qr rd ra; QUERY: 1, ANSWER: 6, AUTHORITY: 0, ADDITIONAL: 0! ! ;; QUESTION SECTION:! ;www.google.com. ! ! !IN !A! ! ;; AN...
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