Rules Syntax

Available options

rule

level

Definition

Specifies the level of the rule. Alerts and responses use this value.

Allowed values

0 to 16

id

Definition

Specifies the ID of the rule.

Allowed values

Any number from 1 to 9999

maxsize

Definition

Specifies the maximum size of the event.

Allowed values

from 1 to 99999

frequency

Definition

Number of times the rule must have matched before firing.

Triggers when 2 more than this setting.

Allowed values

Any number from 1 to 9999

timeframe

Definition

The timeframe in seconds. This option is intended to be used with the frequency option.

Allowed values

Any number from 1 to 9999

ignore

Definition

The time (in seconds) to ignore this rule after firing it (to avoid floods).

Allowed values

Any number from 1 to 9999

overwrite

Definition

Used to supercede an OSSEC rule with local changes.

Allowed values

yes

match

Any string to match against the log event.

Default Value

n/a

Allowed values

Any sregex expression

regex

Any regex to match against the log event.

Default Value

n/a

Allowed values

Any regex expression

decoded_as

Default Value

n/a

Allowed values

Any decoder name

category

The decoded category to match: ids, syslog, firewall, web-log, squid or windows.

Default Value

n/a

Allowed values

Any category

field

Any regex to be compared to a field extracted by the decoder.

name

Specifies the name of the field extracted by the decoder.

srcip

Any IP address or CIDR block to be compared to an IP decoded as srcip. Use “!” to negate it.

Default Value

n/a

Allowed values

Any srcip

dstip

Any IP address or CIDR block to be compared to an IP decoded as dstip. Use “!” to negate it.

Default Value

n/a

Allowed values

Any dstip

extra_data

Any string that is decoded into the extra_data field.

Default Value

n/a

Allowed values

Any string.

user

Any username (decoded as the username).

Default Value

n/a

Allowed values

Any sregex expression

program_name

Program name is decoded from syslog process name.

Default Value

n/a

Allowed values

Any sregex expression

hostname

Any hostname (decoded as the syslog hostname) or log file.

Default Value

n/a

Allowed values

Any sregex expression

time

Time that the event was generated.

Default Value

n/a

Allowed values

Any time range (hh:mm-hh:mm)

weekday

Week day that the event was generated.

Default Value

n/a

Allowed values

monday - sunday, weekdays, weekends

id

Any ID (decoded as the ID).

Default Value

n/a

Allowed values

Any sregex expression

url

Any URL (decoded as the URL).

Default Value

n/a

Allowed values

Any sregex expression

if_sid

Matches if the ID has matched.

Default Value

n/a

Allowed values

Any rule id

if_group

Matches if the group has matched before.

Default Value

n/a

Allowed values

Any Group

if_level

Matches if the level has matched before.

Default Value

n/a

Allowed values

Any level from 1 to 16

if_matched_sid

Matches if an alert of the defined ID has been triggered in a set number of seconds.

This option is used in conjunction with frequency and timeframe.

Default Value

n/a

Allowed values

Any rule id

Note

Rules at level 0 are discarded immediately and will not be used with the if_matched_rules. The level must be at least 1, but the <no_log> option can be added to the rule to make sure it does not get logged.

if_matched_group

Matches if an alert of the defined group has been triggered in a set number of seconds.

This option is used in conjunction with frequency and timeframe.

Default Value

n/a

Allowed values

Any Group

same_id

Specifies that the decoded id must be the same. This option is used in conjunction with frequency and timeframe.

Default Value

n/a

Allowed values

n/a

same_source_ip

Specifies that the decoded source ip must be the same. This option is used in conjunction with frequency and timeframe.

Default Value

n/a

Allowed values

n/a

same_source_port

Specifies that the decoded source port must be the same. This option is used in conjunction with frequency and timeframe.

Default Value

n/a

Allowed values

n/a

same_dst_port

Specifies that the decoded destination port must be the same. This option is used in conjunction with frequency and timeframe.

Default Value

n/a

Allowed values

n/a

same_location

Specifies that the location must be the same. This option is used in conjunction with frequency and timeframe.

Default Value

n/a

Allowed values

n/a

same_user

Specifies that the decoded user must be the same. This option is used in conjunction with frequency and timeframe.

Default Value

n/a

Allowed values

n/a

description

Rule description.

Default Value

n/a

Allowed values

Any string

list

Preform a CDB lookup using an ossec list. This is a fast on disk database which will always find keys within two seeks of the file.

Default Value

n/a

Allowed values

Path to the CDB file to be used for lookup from the OSSEC directory.Must also be included in the ossec.conf file.

Attribute

Description

field

key in the CDB: srcip, srcport, dstip, dstport, extra_data, user, url, id, hostname, program_name, status, action, dynamic field.

lookup

match_key

key to search within the cdb and will match if they key is present. Default.

not_match_key

key to search and will match if it is not present in the database.

match_key_value

searched for in the cdb. It will be compared with regex from attribute check_value.

address_match_key

IP and the key to search within the cdb and will match if they key is present.

not_address_match_key

IP the key to search and will match if it IS NOT present in the database

address_match_key_value

IP to search in the cdb. It will be compared with regex from attribute check_value.

check_value

regex for matching on the value pulled out of the cdb when using types: address_match_key_value, match_key_value

info

Extra information may be added through the following attributes:

Default Value

n/a

Allowed values

Any string

Attribute

Allowed values

Description

type

text

This is the default when no type is selected. Additional,information about the alert/event.

link

Link to more information about the alert/event.

cve

The CVE Number related to this alert/event.

ovsdb

The osvdb id related to this alert/event.

options

Additional rule options

Attribute

Description

alert_by_email

Always alert by email.

no_email_alert

Never alert by email.

no_log

Do not log this alert.

check_diff

Used to determine when the output of a command changes.

Default Value

n/a

Allowed values

n/a

group

Add additional groups to the alert. Groups are optional tags added to alerts.

They can be used by other rules by using if_group or if_matched_group, or by alert parsing tools to categorize alerts.

Default Value

n/a

Allowed values

Any String