Regular Expression Syntax¶

Currently OSSEC supports three regex syntaxes:

pcre2
OS_Regex or regex
OS_Match or sregex

pcre2¶

Information onthe syntax for pcre2 can be found in the pcre documentation.

OS_Regex/regex Syntax¶

Warning

The OSSEC regex syntax is legacy. The preferred method is pcre2 where available.

Fast and simple library for regular expressions in C.

This library is designed to be simple, but support the most common regular expressions. It was designed with intrusion detection systems in mind, where having all options is not crucial, but speed is.

Supported expressions:

\w  ->  A-Z, a-z, 0-9, '-', '@' characters
\d  ->  0-9 characters
\s  ->  For spaces " "
\t  ->  For tabs.
\p  ->  ()*+,-.:;<=>?[]!"'#$%&|{} (punctuation characters)
\W  ->  For anything not \w
\D  ->  For anything not \d
\S  ->  For anything not \s
\.  ->  For anything

Modifiers:

+  ->  To match one or more times (eg \w+ or \d+)
*  ->  To match zero or more times (eg \w* or \p*)

Special Characters:

^ -> To specify the beginning of the text.
$ -> To specify the end of the text.
| -> To create an "OR" between multiple patterns.

Characters Escaping

To utilize the following characters they must be escaped:

$ -> \$
( -> \(
) -> \)
\ -> \\
| -> \|

OS_Match/sregex Syntax¶

Faster than the OS_Regex/regex, but only supports simple string matching and the following special characters.

Special Characters:

^ -> To specify the beginning of the text.
$ -> To specify the end of the text.
| -> To create an "OR" between multiple patterns.