[Snort-users] MISC source port 53 to <1024 question

Rich Adamson radamson at ...2127...
Sun Oct 7 17:41:02 EDT 2001

Wonder if someone can help explain the following rule. I seem to be
getting a lot of what appears to be valid DNS lookups to our primary
DNS server with both a "source and destination port of 53" (as observed
with a Sniffer). (Snort v1.8.1)

alert udp $EXTERNAL_NET 53 -> $HOME_NET :1023 (msg:"MISC source port 53 to <1024"; classtype:bad-unknown; 
sid:515; rev:2;)

The typical alert looks like:

[**] MISC source port 53 to <1024 [**]
10/07-20:02:56.074735 ->
UDP TTL:240 TOS:0x0 ID:29841 IpLen:20 DgmLen:57 DF
Len: 37

Disabling the above rule stops the alerts, but I'm not sure if that is
the right thing to do. The DNS server responds correctly to each of these



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