Value Modifiers and Conditional Field Mapping Bug

[robrankin]

Using value modifiers in a rule appears to conflict with conditional field mappings in a config file. Using the examples:

Set the type: PATH selection to be modified using |contains

title: Edit of .bash_profile and .bashrc
id: e74e15cc-c4b6-4c80-b7eb-dfe49feb7fe9
status: experimental
description: Detects change of user environment. Adversaries can insert code into these files to gain persistence each time a user logs in or opens a new shell.
author: Peter Matkovski
date: 2019/05/12
references:
    - 'MITRE Attack technique T1156; .bash_profile and .bashrc. '
logsource:
    product: linux
    service: auditd
detection:
    selection:
        type|contains: 'PATH'
        name:
            - '/home/*/.bashrc'
            - '/home/*/.bash_profile'
            - '/home/*/.profile'
            - '/etc/profile'
            - '/etc/shells'
            - '/etc/bashrc'
            - '/etc/csh.cshrc'
            - '/etc/csh.login'
    condition: selection
falsepositives:
    - Admin or User activity
level: medium
tags:
    - attack.s0003
    - attack.t1156    # an old one
    - attack.persistence
    - attack.t1546.004

Use a conditional field mapping:

fieldmappings:
    type:
      type=PATH:
        - event.original

Produces the following, incorrect ElastAlert rule, note the type:*PATH* rather than what it should be event.original:*PATH*.

alert:
- debug
description: Detects change of user environment. Adversaries can insert code into these files to gain persistence each time a user logs in or opens a new shell.
filter:
- query:
    query_string:
      query: (event.module:auditd AND type:*PATH* AND auditd.paths.name:(\/home\/*\/.bashrc OR \/home\/*\/.bash_profile OR \/home\/*\/.profile OR \/etc\/profile OR \/etc\/shells OR \/etc\/bashrc OR \/etc\/csh.cshrc OR \/etc\/csh.login))
index: auditbeat-*
name: e74e15cc-c4b6-4c80-b7eb-dfe49feb7fe9-Edit-of-.bash_profile-and-.bashrc
priority: 3
realert:
  minutes: 0
type: any