snort (SID 43687) blocks root DNS servers ?!
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I started seeing DNS query being blocked by snort.
Specifically by SID 43687 blocks IP 192.5.5.241 which resolves to f.root-servers.net by Internet Systems Consortium, Inc.
This looks like a legit root server.
Anybody has any insights on what all this means ?
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It definitely is legit these are the guys that do bind.
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@nogbadthebad any ideas why is it happening ?
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@chudak said in snort (SID 43687) blocks root DNS servers ?!:
SID 43687
https://www.snort.org/rule_docs/1-43687
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@nogbadthebad not sure what you mean...
I did submit false positives for 43687 and 39867, but not sure what's next.
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If you read the web page I linked, something on your network has tried to lookup something who's FQDN ends in .top
Just to prove it do a ping blahblahblah.top from your pc.
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@nogbadthebad said in snort (SID 43687) blocks root DNS servers ?!:
blahblahblah.top
what's "blahblahblah.top" ? and BTW I did disable SIDs as otherwise all DNS blocked
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@chudak said in snort (SID 43687) blocks root DNS servers ?!:
@nogbadthebad said in snort (SID 43687) blocks root DNS servers ?!:
blahblahblah.top
what's "blahblahblah.top" ? and BTW I did disable SIDs as otherwise all DNS blocked
it's just some random FQDN to trigger snort.
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It looks like
"1:43687 INDICATOR-COMPROMISE Suspicious .top dns query" -
Exactly, to ping the host it firstly needs to get the IP address.
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So far it looks like we got no reasonable explanations on what is going on :(
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Yes you have, a device on your network is trying to resolve a suspicious TLD.
If you don’t like what snort is blocking disable the rule that’s triggered the alert.
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@nogbadthebad said in snort (SID 43687) blocks root DNS servers ?!:
Yes you have, a device on your network is trying to resolve a suspicious TLD!
Why do you say "suspicious" vs legit ?
Does this look suspicious to you?
192.5.5.241 which resolves to f.root-servers.net
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The .topTLD does.
https://www.spamhaus.org/statistics/tlds/
Re read the following:-
https://www.snort.org/rule_docs/1-43687
It’s not what up the DNS query is being sent to, it’s what is being queried.
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The end result 192.5.5.241 IP gets blocked.
So how do you resolve this issue then ?
I see sometimes with Sid 1-43687 enabled that none of my PCs can resolve any names and even 8.8.8.8 gets blocked!
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You need to figure out what host is querying the .top TLD maybe increase the logging level of DNS lookups in pfSense.
Do you just run snort on the WAN interface?
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@nogbadthebad Yes this is on WAN
All queries coming from the pfSense router itself and I force all clients to use pfSense router DNS only.
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Enable snort on the LAN as well, you’ll see the host pre NAT.
Otherwise you just see the WAN address.
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@nogbadthebad said in snort (SID 43687) blocks root DNS servers ?!:
Enable snort on the LAN as well, you’ll see the host pre NAT.
Otherwise you just see the WAN address.
I do have LAN enabled as well.
Looked thru logs with Destination IP 192.5.5.241 and found none.
Which is as I'd expect as no clients can do direct DNS queries.???
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Ah I wonder if your not seeing it on the LAN as the source and destination are contained in $HOME_NET
Maybe change the logging level in the DNS Resolver advanced settings.
