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<p class="MsoNormal"><span lang="EN-GB" style="font-family:Consolas;color:#1F497D">Hi,<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB" style="font-family:Consolas;color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB" style="font-family:Consolas;color:#1F497D">You’re right. Another user pointed me in the right direction by suggesting to put in first the negated range:
<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB" style="font-family:Consolas;color:#1F497D">[!$GOOGLE_DNS,$EXTERNAL_NET]<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB" style="font-family:Consolas;color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB" style="font-family:Consolas;color:#1F497D">Which also worked OK. I guess than removing the $EXTERNAL_NET would be better for performance.</span><span lang="EN-GB" style="font-family:Consolas;color:#1F497D"><o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB" style="font-family:Consolas;color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB" style="font-family:Consolas;color:#1F497D">Thank you very much,<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB" style="font-family:Consolas;color:#1F497D">Xavier Romero<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p>
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<p class="MsoNormal"><b><span lang="ES" style="font-size:10.0pt;font-family:"Tahoma","sans-serif"">De:</span></b><span lang="ES" style="font-size:10.0pt;font-family:"Tahoma","sans-serif""> Matt Carothers [mailto:matt@somedamn.com]
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<b>Enviado el:</b> dimecres, 27 d'agost de 2014 17:11<br>
<b>Para:</b> Xavier Romero; oisf-users@lists.openinfosecfoundation.org<br>
<b>Asunto:</b> RE: [Oisf-users] Ignore ips in rule<o:p></o:p></span></p>
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<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><span lang="EN-US" style="color:#1F497D">$EXTERNAL_NET is every IP that isn’t in your $HOME_NET, and that includes the Google DNS servers. It’s like saying [8.8.8.8,!8.8.8.8], which matches both 8.8.8.8 and every IP that isn’t 8.8.8.8,
so it’s always a true condition. You can fix it just by removing the $EXTERNAL_NET, unless your sensor is positioned where it would see port 53 traffic between internal hosts. If that’s the case, you can exclude particular IPs by putting a pass rule ahead
of the alert rule.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="color:#1F497D">- Matt<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="color:#1F497D"><o:p> </o:p></span></p>
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<p class="MsoNormal"><b><span lang="EN-US" style="font-size:10.0pt;font-family:"Tahoma","sans-serif"">From:</span></b><span lang="EN-US" style="font-size:10.0pt;font-family:"Tahoma","sans-serif"">
<a href="mailto:oisf-users-bounces@lists.openinfosecfoundation.org">oisf-users-bounces@lists.openinfosecfoundation.org</a> [<a href="mailto:oisf-users-bounces@lists.openinfosecfoundation.org">mailto:oisf-users-bounces@lists.openinfosecfoundation.org</a>]
<b>On Behalf Of </b>Xavier Romero<br>
<b>Sent:</b> Wednesday, August 27, 2014 4:40 AM<br>
<b>To:</b> <a href="mailto:oisf-users@lists.openinfosecfoundation.org">oisf-users@lists.openinfosecfoundation.org</a><br>
<b>Subject:</b> [Oisf-users] Ignore ips in rule<o:p></o:p></span></p>
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<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal">Hello,<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">I’ve this custom rule:<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><span style="font-size:10.0pt;font-family:Consolas">...<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="RU" style="font-size:10.0pt;font-family:Consolas">alert udp [$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;)</span><span style="font-size:10.0pt;font-family:Consolas"><o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:10.0pt;font-family:Consolas">...<o:p></o:p></span></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">And this definition on suricata.yaml:<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><span style="font-size:9.0pt;font-family:Consolas">...<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:9.0pt;font-family:Consolas"># Holds variables that would be used by the engine.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:9.0pt;font-family:Consolas">vars:<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:9.0pt;font-family:Consolas"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:9.0pt;font-family:Consolas"> # Holds the address group vars that would be passed in a Signature.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:9.0pt;font-family:Consolas"> # These would be retrieved during the Signature address parsing stage.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:9.0pt;font-family:Consolas"> address-groups:<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:9.0pt;font-family:Consolas"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:9.0pt;font-family:Consolas"> HOME_NET: "[x.x.x.x/24]"<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:9.0pt;font-family:Consolas"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:9.0pt;font-family:Consolas"> GOOGLE_DNS: "[8.8.8.8,8.8.4.4]"<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:9.0pt;font-family:Consolas"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:9.0pt;font-family:Consolas"> EXTERNAL_NET: "!$HOME_NET"<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:9.0pt;font-family:Consolas"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:9.0pt;font-family:Consolas"> HTTP_SERVERS: "$HOME_NET"<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:9.0pt;font-family:Consolas"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:9.0pt;font-family:Consolas"> SMTP_SERVERS: "$HOME_NET"<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:9.0pt;font-family:Consolas"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:9.0pt;font-family:Consolas"> SQL_SERVERS: "$HOME_NET"<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:9.0pt;font-family:Consolas"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:9.0pt;font-family:Consolas"> DNS_SERVERS: "[a.a.a.a,b.b.b.b,c.c.c.c,d.d.d.d]"<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:9.0pt;font-family:Consolas"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:9.0pt;font-family:Consolas"> TELNET_SERVERS: "$HOME_NET"<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:9.0pt;font-family:Consolas">...<o:p></o:p></span></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">However, there are alerts like these:<o:p></o:p></p>
<p class="MsoNormal"><span style="font-size:9.0pt;font-family:Consolas">...<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:9.0pt;font-family:Consolas">08/27/2014-10:33:37.344581 [**] [1:101111009:5] Possible atac DNS [**] [Classification: Attempted Denial of Service] [Priority: 2] {UDP} 8.8.8.8:53 -> a.b.c.d:52721<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:9.0pt;font-family:Consolas">08/27/2014-10:33:48.511591 [**] [1:101111009:5] Possible atac DNS [**] [Classification: Attempted Denial of Service] [Priority: 2] {UDP} 8.8.8.8:53 -> a.b.c.d:35899<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:9.0pt;font-family:Consolas">...<o:p></o:p></span></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">I’m expecting to totally ignore packets whith IP source 8.8.8.8. What I’m doing wrong?<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">I’ve also tried<o:p></o:p></p>
<p class="MsoNormal"><span style="font-size:9.0pt;font-family:Consolas"> </span>
<span lang="RU" style="font-size:9.0pt;font-family:Consolas">[$EXTERNAL_NET,!</span><span style="font-size:9.0pt;font-family:Consolas">[8.8.8.8,8.8.4.4]</span><span lang="RU" style="font-size:9.0pt;font-family:Consolas">]</span><span style="font-size:9.0pt;font-family:Consolas"><o:p></o:p></span></p>
<p class="MsoNormal">Instead of:<o:p></o:p></p>
<p class="MsoNormal"><span style="font-size:9.0pt;font-family:Consolas"> </span><span lang="RU" style="font-size:9.0pt;font-family:Consolas">[$EXTERNAL_NET,!$GOOGLE_DNS]</span><span style="font-size:10.0pt"><o:p></o:p></span></p>
<p class="MsoNormal">With the same result.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Each time I modify the rule, I increment REV number and restart suricata.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Thank you very much,<o:p></o:p></p>
<p class="MsoNormal">Xavier Romero<o:p></o:p></p>
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