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siembol_alerting_services.md

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Siembol Alerting Services

Overview

Siembol alert is a detection engine used to filter matching events from an incoming data stream based on a configurable rule set. The correlation alert allows you to group several detections together before raising an alert.

Alert service

Common rule fields

The fields that are common to alert and correlation alert.

  • rule_name - Rule name that uniquely identifies the rule
  • rule_author - The author of the rule - the user who last modified the rule
  • rule_version - The version of the rule
  • rule_description - This field contains a single text input that allows you set a description for the alert. This should be a short, helpful comment that allows anyone to identify the purpose of this alert.
  • tags - Tags are optional but recommended as they allow you to add tags to the event after matching the rule. Each tag is a key-value pair. Both the key and the value inputs are completely free form allowing you to tag your rules in the way which works best for your organisation. You can use substitution in the value input to set the tag value equal to the value of a field from the event. The syntax for this is ${field_name}
    • tag_name - The name of the tag
    • tag_value - The value of the tag.
Note: if you want to correlate an alert in correlation engine that use the tag with name "correlation_key". This alert will be silent if you do not set the tag with name "correlation_alert_visible"
  • rule_protection - Rule Protection allows you to prevent a noisy alert from flooding the components downstream. You can set the maximum number of times an alert can fire per hour and per day. If either limit is exceeded then any event that matches is sent to error instead of output topic until the threshold is reset. Rule Protection is optional. If it is not configured for a rule, the rule will get the global defaults applied.
    • max_per_hour - Maximum alerts allowed per hour
    • max_per_day - Maximum alerts allowed per day

Alert rule

  • source_type - This fields allows you to determine the type of data you want to match on. It is essentially a matcher for the "source_type" field. This field does not support regex - however, using * as an input matches all source types. The source_type field is set during parsing and is equal to the name of the last parser which was used to parse the log.
Tip: if you want to match on multiple data sources, set the source type to be * and add a regex matcher (in the matcher section) to filter down to your desired source types.

Matchers

Matchers allow you to select the events you want the rule to alert on.

  • is_enabled - The matcher is enabled
  • description - The description of the matcher
  • matcher_type - Type of matcher, either REGEX_MATCH, IS_IN_SET, CONTAINS, NUMERIC_COMPARE, COMPOSITE_AND or COMPOSITE_OR
  • is_negated- The matcher is negated private Boolean negated = false;
  • field - The name of the field on which the matcher will be evaluated

There are four types of matchers:

  • REGEX_MATCH - A regex_match allows you use a regex statement to match a specified field. There are two string inputs:
  • IS_IN_SET - An "is_in_set" matcher compares the value of a field to a set of strings defined in data. If the value is in the set then the matcher returns true.
    • data - A list of strings to compare the value to. New line delimited. Does not support regex - each line must be a literal match however, field substitution is supported in this field.
    • case_insensitive- Use case-insensitive string compare
  • CONTAINS - A "contains" matcher searches for substring defined in data. If the pattern is found the matcher returns true.
    • data - A pattern to search. Field substitution is supported in this field.
    • case_insensitive - Use case-insensitive string compare
    • starts_with- The field value starts with the pattern
    • ends_with - The field value ends with the pattern
  • NUMERIC_COMPARE - A matcher compares field numeric value with the expression using various comparing types
    • compare_type - The type of comparing numbers, either equal, lesser_equal, lesser, greater or greater_equal
    • expression - A field numeric value will be compared with the expression. The expression can be a numeric constant or a string that contains a variable.
  • COMPOSITE_AND - Used to combine matchers from the list matchers with AND logic operation
  • COMPOSITE_OR - Used to combine matchers from the list matchers with OR logic operation

Note : A composite matcher is recursive in alerting engine, however the level of recursion is limited to 3 in Siembol UI for simplicity

Global Tags and Rule Protection

Global tags and global rule protection are defined in the deployment of the rules. These are added to the alert after matching unless are overridden by individual rule settings. The global tag with the name detection_source is used to identify the detection engine that triggers the alert.

Correlation Rule

Overview

The correlation alert allows you to group several detections together before raising an alert. The primary use case for this is when you have a group of detections which individually shouldn't be alerted on (e.g. high volume or detections with high false positive rate) you can group several together to get more reliable alerts.

Correlation alert rule

correlation_attributes field allows you to configure which detections to correlate together.

  • time_unit - A field that allows you to configure the time unit to use, this is a fixed option with the choices:
    • hours
    • minutes
    • seconds
  • time_window - A field to set the time window in the selected time unit for the correlation
  • time_computation_type - You can configure how the time window is calculated
    • event_time - The time window is calculated using the timestamp field in the events, the timestamp field is usually computed during parsing from the log
    • processing_time - The time window is calculated using the current time (when an alert is evaluated), the events need to be processed by the correlation alert component within the time window
  • max_time_lag_in_sec - The event with timestamp older than the current time minus the lag (in seconds) will be discarded
  • alerts_threshold - The alert's threshold allows you to configure how many detections (you can specify which detections later) need to trigger in the time window for the alert to trigger. This field accepts an integer value, if it is left empty then all detections need to trigger before an alert is created
    • alerts - The list of alerts for correlation
      • alert - The alert name used for correlation
      • threshold - The number of times the alert has to trigger in the time window
      • mandatory - The alert must pass the threshold for the rule to match
  • fields_to_send - The list of fields of correlated alerts that will be included in the triggered alert after matching

Admin config

Common admin config fields

  • alerts.topology.name - The name of storm topology
  • alerts.input.topics - The list of kafka input topics for reading messages
  • kafka.error.topic - The kafka error topic for error messages
  • alerts.output.topic - The kafka output topic for publishing alerts
  • alerts.correlation.output.topic - The kafka topic for alerts used for correlation by correlation rules
  • kafka.producer.properties - Defines kafka producer properties, see https://kafka.apache.org/0102/documentation.html#producerconfigs
  • zookeeper.attributes - The zookeeper attributes for updating the rules
    • zk.url - Zookeeper servers url. Multiple servers are separated by comma
    • zk.path - Path to a zookeeper node or multiple nodes delimited by new line. Alerting rules from multiple zookeeper nodes can be loaded in order to save storm resources
  • storm.attributes - Storm attributes for the enrichment topology
  • kafka.spout.num.executors - The number of executors for reading from kafka input topic
  • alerts.engine.bolt.num.executors - The number of executors for evaluating alerting rules
  • kafka.writer.bolt.num.executors - The number of executors for producing alerts to output topic

Alert admin config

  • alerts.engine - This field should be set to siembol_alerts

Correlation alert admin config

  • alerts.engine - This field should be set to siembol_correlation_alerts
  • alerts.engine.clean.interval.sec - The period in seconds for regular cleaning a rule correlation data that are not needed for the further rule evaluation