Logwatch: Ignore certain IPs for SSH & PAM checks?

Question

I have a CentOS 5.6 system, which runs Logwatch.

If I perform a security scan (Nessus) against this host, it produces unnecessary noise in the Logwatch output. I'd like to run these security scans regularly, from an internal IP and an external IP, without generating unnecessary noise about the security scans.

Since I know the IPs of these hosts, can I prevent this output from showing up in the Logwatch output?

 --------------------- pam_unix Begin ------------------------

 sshd:
   Authentication Failures:
      root (scan1.example.org): 1 Time(s)
      unknown (scan1.example.org): 1 Time(s)
   Invalid Users:
      Unknown Account: 1 Time(s)

--------------------- SSHD Begin ------------------------


 Failed logins from:
   192.168.100.1 (scan1.example.org): 1 time

 Illegal users from:
   X.Y.123.123 (scan2.example.org): 1 time

 **Unmatched Entries**
 pam_succeed_if(sshd:auth): error retrieving information about user admin : 1 time(s)
 fatal: Write failed: Connection reset by peer : 1 time(s)

Answer 1

Logwatch provides the *Remove shared script which will tell Logwatch to ignore lines which contain a particular string (e.g. grep -v), before they are processed later on.

1. Copy /usr/share/logwatch/default.conf/services/sshd.conf to /etc/logwatch/conf/services/sshd.conf
2. Add the following lines, which will tell logwatch to not process log entries for lines which contain this string:

# Ignore these hosts
*Remove = 192.168.100.1
*Remove = X.Y.123.123
# Ignore these usernames
*Remove = testuser

3. Now, no logwatch messages are generated for these hosts.

I couldn't do this with ignore.conf. I cannot come up with a regular expression which will allow Logwatch to print messages about attacks from evil domains:

Failed logins from:
   11.12.100.1 (EVILSCAN.example.ru): 1 time

While hiding messages generated by friendly scanners:

Failed logins from:
   192.168.100.1 (friendscan.example.org): 1 time

Background:

The Logwatch methods to do this are very poorly documented, and are not well googleable.

The shared script at /usr/share/logwatch/scripts/shared/remove will perform an inverse grep on a string. /usr/share/doc/logwatch-*/HOWTO-Customize-LogWatch documents how to execute these scripts:

You can have commands in the form of:

*SharedScriptName = Arguments

that will execute a script found in the /usr/share/logwatch/scripts/shared/directory named 'SharedScriptName' with arguments 'Arguments'.This filter will modify the input to the service's filter.

Answer 2

You could place regexp to ignore log lines into /etc/logwatch/conf/ignore.conf