OSSEC | How to add an exception rule

Question

I have the standard syslog_rules.xml (OSSEC 2.6.0). This is the standard rule for bad words in the /var/log/messages file:

<var name="BAD_WORDS">core_dumped|failure|error|attack|bad |illegal |denied|refused|unauthorized|fatal|failed|Segmentation Fault|Corrupted</var>
.....    
<rule id="1002" level="2">
<match>$BAD_WORDS</match>
<options>alert_by_email</options>
<description>Unknown problem somewhere in the system.</description>
</rule>
.....

How can I add or modify this rule that uses $BAD_WORDS, but excludes the auxpropfunc error phrase? That is, something like this:

<match>$BAD_WORDS</match>
<match>!auxpropfunc error</match>
<options>alert_by_email</options>

Any ideas?

Answer 1

Your best option is probably to write a rule to ignore that phrase. You could add something like the following to /var/ossec/rules/local_rules.xml:

<rule id="SOMETHING" level="0">
  <if_sid>1002</if_sid>
  <match>auxpropfunc error</match>
  <description>Ignore auxpropfunc error.</description>
</rule>

You could then run the entire log message through ossec-logtest to see how OSSEC will analyze it. You may need to add another option into this rule, or you may not.

Answer 2

If you have more than one word, you could add something like the following to /var/ossec/rules/local_rules.xml

<var name="GOOD_WORDS">error_reporting|auxpropfunc error</var>

<rule id="100002" level="0">
  <if_sid>1002</if_sid>
  <match>$GOOD_WORDS</match>
  <description>Ignore good_words.</description>
</rule>