Configuring the YARA rule weight default using the CLI

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By default, every custom YARA rule has an integer weight associated with it, ranging from 0 to 100. During static analysis, when a YARA rule match is made, the corresponding weight of the matched rule is added to the overall score of the file deemed malicious. As more YARA rules are matched, the rule with the highest weight is used. If no weight is provided for a YARA rule, the default YARA weight is used.

Trellix reports when the rule matches (if it is one of the first five rules matched). YARA rules with a weight of 0 are generally used for informational purposes (for example, when a file is a malformed Win32 portable executable).

Prerequisites

  • An established connection between the File Protect appliance and the Internet.

  • Administrator or Operator access to the File Protect appliance.

To configure the YARA rule weight default:
  1. Go to CLI configuration mode.

    hostname > enable
    hostname # configure terminal
  2. Specify the limit for YARA matches.

    hostname (config) # yara weight default <100 +/-> 

    where:

    <100 +/-> is an integer between 0 and 100.

    The following example configures a YARA weight of 75:

    hostname (config) # yara weight default 75