[Snort-users] Local rules with same sids and snort works!

Joel Esler (jesler) jesler at ...589...
Wed Nov 9 13:59:58 EST 2016


I apologize, I believe I misspoke in saying it takes the “first SID” it encounters with the same rev.  It’s obviously taking the last one it read.  That’s my fault.

--
Joel Esler | Talos: Manager | jesler at ...589...<mailto:jesler at ...589...>






On Nov 9, 2016, at 1:58 PM, fatema bannatwala <fatema.bannatwala at ...11827...<mailto:fatema.bannatwala at ...11827...>> wrote:

First and second in my local.rules file.
I thought the snort would read the local.rules file sequentially and hence would encounter the rules sequentially while start up, hence was referring "first"as first in local.rules.

~]$ less local.rules
# ------------
# LOCAL RULES
# ------------
# This file intentionally does not come with signatures.  Put your local
# additions here.

alert tcp $EXTERNAL_NET any -> $HOME_NET $HTTP_PORTS (msg:"HTTP Proxy client detected"; flow: to_server,established; content:"X-Forwarded-"; http_header; reference:url,http://www.forensicswiki.org/wiki/Proxy_server; classtype:policy-violation; sid:10001030; rev:1;)

alert tcp $HOME_NET any -> $EXTERNAL_NET $HTTP_PORTS (msg:"UDel Likely Successful Generic Phish 2016-09-23"; flow:to_server,established; content:"POST"; http_method; content:".php"; http_uri; content:"netid="; depth:10; fast_pattern; http_client_body; content:"&pword="; distance:0; classtype:trojan-activity; sid:10001030; rev:1;)


On Wed, Nov 9, 2016 at 1:52 PM, Joel Esler (jesler) <jesler at ...589...<mailto:jesler at ...589...>> wrote:
You mean, “first” and “second” in the email?  Or first and second, as Snort encounters them in order on startup?

--
Joel Esler | Talos: Manager | jesler at ...589...<mailto:jesler at ...589...>






On Nov 9, 2016, at 1:40 PM, fatema bannatwala <fatema.bannatwala at ...11827...<mailto:fatema.bannatwala at ...11827...>> wrote:

Well, the rules have same rev numbers, and the order is like this:

alert tcp $EXTERNAL_NET any -> $HOME_NET $HTTP_PORTS (msg:"HTTP Proxy client detected"; flow: to_server,established; content:"X-Forwarded-"; http_header; reference:url,http:/           /www.forensicswiki.org/wiki/Proxy_server<http://www.forensicswiki.org/wiki/Proxy_server>; classtype:policy-violation; sid:10001030; rev:1;)

alert tcp $HOME_NET any -> $EXTERNAL_NET $HTTP_PORTS (msg:"Custom Likely Successful Generic Phish 2016-09-23"; flow:to_server,established; content:"POST"; http_method; content:".php"; http_uri; content:"netid="; depth:10; fast_pattern; http_client_body; content:"&pword="; distance:0; classtype:trojan-activity; sid:10001030; rev:1;)

I only get alerts from the second one now, i.e phishing one, and haven't gotten any alert triggered for the first rule.
Previously, when I had only the first rule, I used to get lot of alerts for people using proxy, but ever since the second alert got added I realized that the first rule stopped triggering anymore.

On Wed, Nov 9, 2016 at 1:28 PM, Joel Esler (jesler) <jesler at ...589...<mailto:jesler at ...589...>> wrote:
You can have duplicate SIDS.  The rule with the highest rev will override the lower rev rule, otherwise Snort will take the first rule it gets to, and ignore the other one.

It’s been this way for several years.


--
Joel Esler | Talos: Manager | jesler at ...589...<mailto:jesler at ...589...>






On Nov 9, 2016, at 1:19 PM, fatema bannatwala <fatema.bannatwala at ...11827...<mailto:fatema.bannatwala at ...11827...>> wrote:

Hi All,

Just realized that I have two rules in my local.rules file with same sid, and snort works just fine!!
I always had in my head that sids should have to be unique, but today when I was going through the local.rules file, I realized that someone from our team had created a new rule and assigned it a same sid that a previous rule had.
I couldn't catch it before because snort was running just fine without any complains on duplicate sids.

Have I missed this change in the current (or 2.9 version) of snort or is it something else?

Quick points: I have local.rules enabled in snort.conf and pulled pork is not modifying anything regarding local rules so they should get loaded as it is, and above all I am getting alerts for one of the rules having duplicate sid, but no alerts for the other rule having same sid.

Snort version - 2.9.8.3
barnyard version - 2-1.9
pulledpork - 0.7.0

Thanks,
Fatema.
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