[Oisf-users] Ignore ips in rule

Xavier Romero XRomero at nexica.com
Wed Aug 27 08:40:16 UTC 2014


I've this custom rule:

alert udp [$EXTERNAL_NET,!$GOOGLE_DNS] 53 -> [$HOME_NET,!$DNS_SERVERS] any (msg:"Possible atac DNS"; threshold: type both, track by_dst, count 600, seconds 60; classtype:attempted-dos; sid:101111009; rev:5;)

And this definition on suricata.yaml:

# Holds variables that would be used by the engine.

  # Holds the address group vars that would be passed in a Signature.
  # These would be retrieved during the Signature address parsing stage.

    HOME_NET: "[x.x.x.x/24]"

    GOOGLE_DNS: "[,]"





    DNS_SERVERS: "[a.a.a.a,b.b.b.b,c.c.c.c,d.d.d.d]"


However, there are alerts like these:
08/27/2014-10:33:37.344581  [**] [1:101111009:5] Possible atac DNS [**] [Classification: Attempted Denial of Service] [Priority: 2] {UDP} -> a.b.c.d:52721
08/27/2014-10:33:48.511591  [**] [1:101111009:5] Possible atac DNS [**] [Classification: Attempted Denial of Service] [Priority: 2] {UDP} -> a.b.c.d:35899

I'm expecting to totally ignore packets whith IP source What I'm doing wrong?

I've also tried
Instead of:
With the same result.

Each time I modify the rule, I increment REV number and restart suricata.

Thank you very much,
Xavier Romero
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