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Improve DNS analysis.

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- Fix parsing of empty question sections (when QDCOUNT == 0).  In this
  case, the DNS parser would extract two 2-byte fields for use in either
  "dns_query_reply" or "dns_rejected" events (dependent on value of
  RCODE) as qclass and qtype parameters.  This is not correct, because
  such fields don't actually exist in the DNS message format when
  QDCOUNT is 0.  As a result, these events are no longer raised when
  there's an empty question section.  Scripts that depends on checking
  for an empty question section can do that in the "dns_message" event.

- Add a new "dns_unknown_reply" event, for when Bro does not know how
  to fully parse a particular resource record type.  This helps fix a
  problem in the default DNS scripts where the logic to complete
  request-reply pair matching doesn't work because it's waiting on more
  RR events to complete the reply.  i.e. it expects ANCOUNT number of
  dns_*_reply events and will wait until it gets that many before
  completing a request-reply pair and logging it to dns.log.  This could
  cause bogus replies to match a previous request if they happen to
  share a DNS transaction ID.
This commit is contained in:
Jon Siwek 2014-01-28 11:04:01 -06:00
parent 392d1cb759
commit 0e0e74e49c
7 changed files with 61 additions and 30 deletions
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6
testing/btest/Baseline/scripts.base.protocols.dns.dns-key/dns.log
View file

@ -3,8 +3,8 @@
#empty_field (empty)
#unset_field -
#path dns
#open 2013-08-26-19-04-08
#open 2014-01-28-14-55-04
#fields ts uid id.orig_h id.orig_p id.resp_h id.resp_p proto trans_id query qclass qclass_name qtype qtype_name rcode rcode_name AA TC RD RA Z answers TTLs rejected
#types time string addr port addr port enum count string count string count string count string bool bool bool bool count vector[string] vector[interval] bool
1359565680.761790 CXWv6p3arKYeMETxOg 192.168.6.10 53209 192.168.129.36 53 udp 41477 paypal.com 1 C_INTERNET 48 DNSKEY 0 NOERROR F F T F 1 - - F
#close 2013-08-26-19-04-08
1359565680.761790 CXWv6p3arKYeMETxOg 192.168.6.10 53209 192.168.129.36 53 udp 41477 paypal.com 1 C_INTERNET 48 DNSKEY 0 NOERROR F F T T 1 <unknown type=48>,<unknown type=48>,<unknown type=46>,<unknown type=46> 455.000000,455.000000,455.000000,455.000000 F
#close 2014-01-28-14-55-04