KFSensor can import rules written in Snort format.
There are a number of different sources for Snort rules and the first stage is to download copies of different rule sets.
Unlike a network IDS, KFSensor uses signatures to provide information on an attack and not to identify attacks. It is therefore possible to use experimental and non-certified rule sets.
The official Snort and community rules sets can be obtained at:
Another important source of rules is Bleeding Snort:
There are other specialised rule sets available on the Internet and it is also possible to write your own.
Snort rules are distributed in text files with a .rules extension.
Snort rules may come with a snort.conf file that acts as a master file for the rule files.
These are often packaged in a .tar.gz format.
If the downloaded rule set is in this format then use a program such as WinZip to extract the rule files to a new directory.
N.B. If using WinZip then make sure the "Use Folder Names" option is checked.
The KFSensor signature engine is very fast and should not impact on performance of the system, even with over 3,000 rules loaded.
When a large rule base is loaded there is however a performance hit when the system first starts up or is re-started. A large rule base may cause a delay of several seconds when KFSensor starts up.
Rule sets are frequently updated with new and revised rules.
Updating the KFSensor rule base is simply a matter of downloading the new version of the complete rule set and repeating the import process described above.
The Import Signatures dialog will automatically compare the rules in the import
file with those in the rule base.
Existing rules are excluded by default, making it easy to identify and select the new and revised rules to import. When importing revised rules the previous version of a rule is automatically archived.
After several updates the number of archived rules may grow.
Purging the archived rules is not essential, but it will improve KFSensor's start up performance.
To do this use the Purge button on the Edit Signatures dialog box.
As public signatures are frequently updated it is a desirable to automate this process.
This page describes the tools and configuration needed to fully automate this process.
|1||Download the latest rule sets from one
or more public or private sources
|2||Unpack the rule sets||kfrulemaster|
|3||Update the Kfsensor signature base with new and updated rules||kfsigimp|
|4||Reload the KFSensor server with the latest rules||Automatic|
|5||Delete the unpacked source rules||kfrulemaster|
kfrulemaster is a perl script the handles the downloading and unpacking of snort rule sets.
It calls kfsigimp to perform the update of the rule base and then deletes the downloaded rules.
kfsigimp is a console based utility shipped with KFSensor.
Once the signature base has been updated the KFSensor Server detects this and reloads the rules automatically. There is no need to restart the server manually.
In order to run kfrulemaster it is necessary to install Perl.
We recommend ActiveState's ActivePerl distribution, as it is pre-configured with all the perl modules required by kfrulemaster.
This can be easily achieved by setting up a task in Windows Scheduled Tasks feature. However the Task Scheduler service will be disabled in a fully locked down Windows machine.
An alternative scheduler is needed on a locked down machine and there are several available.
We recommend the freeware nnCron LITE from nnSoft: http://www.nncron.ru/
The utility is located by default in this path:
kfsigimp requires either -i or -v options to be specified. The verify option does everything apart from re-writing the signature file and is useful for testing.
One or more rule files/directories can be listed on the command line. If a directory is specified then the utility will search for all *.rules files in that directory and in its sub-directories and process them all. It is more efficient to run the utility once for all the rule file to be loaded. The kfrulemaster script places all unpacked files underneath a single temporary directory and calls kfsigimp to process them all.
If no sigfilepath is specified then the active KFSensor signature will be updated.
kfsigimp writes to a log file, C:\kfsensor\logs\kfsigimp.log, which details each file processed and the number of rules updated.