Rules classification

The rules are classified in multiple levels, from the lowest (0) to the maximum (16). Some levels are not used at this moment. The following table describes each one, which can be useful to understand the severity of each triggered alert or creating custom rules.

Level

Title

Description

0

Ignored

No action taken. Used to avoid false positives.

These rules are scanned before all the others.

Include events with no security relevance.

2

System low priority notification

System notification or status messages. These have no security relevance.

3

Successful/Authorized events

These include successful login attempts, firewall allow events, etc.

4

System low priority error

Errors related to bad configurations or unused devices/applications.

These have no security relevance and are usually caused by default installations or software testing.

5

User generated error

These include missed passwords, denied actions, etc. By themselves, these have no security relevance.

6

Low relevance attack

These indicate a worm or a virus that have no affect to the system (like code red for apache servers, etc).

These also include frequently IDS events and frequently errors.

7

“Bad word” matching

These include words like “bad”, “error”, etc.

These events are most of the time unclassified and may have some security relevance.

8

First time seen

Include first time seen events. First time an IDS event is fired or the first time an user logged in.

It also includes security relevant actions (like the starting of a sniffer or something like that).

9

Error from invalid source

Include attempts to login as an unknown user or from an invalid source.

May have security relevance (specially if repeated).

These also include errors regarding the “admin” (root) account.

10

Multiple user generated errors

These include multiple bad passwords, multiple failed logins, etc.

These may indicate an attack or may just be that a user just forgot his credentials.

11

Integrity checking warning

These include messages regarding the modification of binaries or the presence of rootkits (by Rootcheck).

These may indicate a successful attack. Also included IDS events that will be ignored (high number of repetitions).

12

High importance event

These include error or warning messages from the system, kernel, etc.

These may indicate an attack against a specific application.

13

Unusual error (high importance)

Most of the times it matches a common attack pattern.

14

High importance security event

Most of the times done with correlation and it indicates an attack.

15

Severe attack

No chances of false positives. Immediate attention is necessary.