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Predicates

A predicate is a filter made of conditions formed by SP-Lang expressions.

How to write predicates

Before you can create a filter, you need to know the possible fields and values of the logs you are looking for. To see what fields and values your logs have, go to Discover in the TeskaLabs LogMan.io web app.

SP-Lang expressions

Construct conditions for the filter using SP-Lang expressions. The filter checks the incoming log to see if the log makes the expressions "true" and therefore meets the conditions.

You can find the full SP-Lang documentation here.

Common SP-Lang expressions:

Expression Meaning
!AND ALL of the criteria nested under !AND must be met for the !AND to be true
!OR At least ONE of the criteria nested under !OR must be met for the !OR to be true
!EQ "Equal" to. Must be equal to, or match the value, to be true
!NE "Not equal" to, or doesn't equal. Must NOT equal (must not match the value) to be true
!IN Looks for a value in a set of values (what in where)
!STARTSWITH The value of the field (what) must start with the specified text (prefix) to be true
!ENDSWITH The value of the field (what) must end with the specified text (postfix) to be true
!ITEM EVENT Gets information from the content of the incoming logs (allows the filter to access the fields and values in the incoming logs)
!NOT Seeks the opposite of the expression nested under the !NOT (following what)

Conditions

Use this guide to structure your individual conditions correctly.

Parentheses

Words in parentheses () are placeholders to show where values go. SP-Lang does not use parentheses.

Filter for a log that: SP-Lang
Has a specified value in a specified field 
    - !EQ
      - !ITEM EVENT (field)
      - "(value)"
Has a specified field 
  - !IN
    what: (field)
    where: !EVENT
Does NOT have a specified value in a specified field 
  - !NE
    - !ITEM EVENT (field)
    - "(value)"
Has one of multiple possible values in a field 
  - !OR
    - !EQ
      - !ITEM EVENT (field)
      - "(value1)"
    - !EQ
      - !ITEM EVENT (field)
      - "(value2)"
Has a specified value that begins with a specified number or text (prefix), in a specified field 
  !STARTSWITH
    what: !ITEM EVENT (field)
    prefix: "(prefix)"
Has a specified value that ends with a specified number or text (postfix), in a specified field 
  !ENDSWITH
    what: !ITEM EVENT (field)
    prefix: "(postfix)"
Does NOT satisfy a condition or set of conditions 
  - !NOT
    what:
      !(SP-Lang expression/s)

Example

To learn what each expression means in the context of this example, click the icons.

  !AND #(1)
  - !OR #(2)
    - !EQ
      - !ITEM EVENT event.dataset
      - "sophos"
    - !EQ
      - !ITEM EVENT event.dataset
      - "vmware-vcenter"
  - !OR #(3)
    - !EQ
      - !ITEM EVENT event.action
      - "Authentication failed"
    - !EQ
      - !ITEM EVENT event.action
      - "failed password"
    - !EQ
      - !ITEM EVENT event.action
      - "unsuccessful login"
  - !OR #(4)
    - !IN
      what: source.ip
      where: !EVENT
    - !IN
      what: user.id
      where: !EVENT
  - !NOT #(5)
    what:
      !STARTSWITH
      what: !ITEM EVENT user.id
      prefix: "harry"
  1. Every expression nested under !AND must be true for a log to pass through this filter.
  2. In the log, in the field event.dataset, the value must be sophos or vmware-vcenter for this !OR to be true.
  3. In the log, in the field event.action, the value must be Authentication failed, failed password, or unsuccessful login for this !OR to be true.
  4. The log must contain the field source.ip or the field user.id for this !OR to be true.
  5. In the log, the field user.id must not begin with harry for this !NOT to be true.

This filters for logs that:

  • Have the value sophos or vmware-vcenter in the field event.dataset AND
  • Have the value Authentication failed, failed password, or unsuccessful login in the field event.action AND
  • Include at least one of the fields source.ip or user.id AND
  • Do not have a value that begins with harry in the field user.id

For more ideas and formatting tips, see this example in the context of a detection rule, including details about the predicate section.