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Detection rules › YARA-L

Okta MFA Bruteforce Attack

Severity
medium
Type
Hunt
Time window
15m
Match by
parent_session_id
Author
Google Cloud Security
Source
github.com/chronicle/detection-rules

Detects a successful login after multiple failed MFA pushes

MITRE ATT&CK coverage

TacticTechniques
Credential Access

References

Telemetry coverage

PlatformRecord / event type
OktaSystem Log event type system.push.send_factor_verify_push: Push notification sent for factor verification
OktaSystem Log event type user.authentication.auth_via_mfa: User authenticated via MFA

Rules detecting the same action

These rules filter on the same operation.

Rule body

// Copyright 2023 Google LLC. Licensed under Apache-2.0.

rule okta_mfa_brute_force_attack {

  meta:
    author = "Google Cloud Security"
    description = "Detects a successful login after multiple failed MFA pushes"
    rule_id = "mr_61d8d679-bf4d-4441-bbbb-65f82a37e3c5"
    rule_name = "Okta MFA Bruteforce Attack"
    reference = "https://sec.okta.com/pushfatigueworkflows"
    mitre_attack_tactic = "Credential Access"
    mitre_attack_technique = "Brute Force"
    mitre_attack_url = "https://attack.mitre.org/techniques/T1110/"
    mitre_attack_version = "v13.1"
    type = "Hunt"
    data_source = "Okta"
    severity = "Medium"
    priority = "Medium"

  events:
    $push.metadata.product_name = "Okta"
    $push.metadata.vendor_name = "Okta"
    $push.metadata.event_type = "USER_UNCATEGORIZED"
    $push.metadata.product_event_type = "system.push.send_factor_verify_push"
    $push.network.parent_session_id = $parent_session_id

    $auth.metadata.event_type = "USER_LOGIN"
    $auth.metadata.product_event_type = "user.authentication.auth_via_mfa"
    $auth.metadata.product_name = "Okta"
    $auth.metadata.vendor_name = "Okta"
    $auth.security_result.action = "ALLOW"
    $auth.network.parent_session_id = $parent_session_id

    $push.metadata.event_timestamp.seconds <= $auth.metadata.event_timestamp.seconds

  match:
    $parent_session_id over 15m

  outcome:
    $risk_score = max(35)
    $mitre_attack_tactic = "Credential Access"
    $mitre_attack_technique = "Brute Force"
    $push_target_user_agent = array_distinct($push.network.http.user_agent)
    $push_principal_ip = array_distinct($push.principal.ip)
    $push_principal_ip_country = array_distinct($push.principal.ip_geo_artifact.location.country_or_region)
    $push_principal_ip_state = array_distinct($push.principal.ip_geo_artifact.location.state)
    //$push_principal_ip_city = array_distinct($push.principal.location.city)
    $push_principal_user_email_addresses = array_distinct ($push.principal.user.email_addresses)
    $push_security_result_summary = array_distinct($push.security_result.summary)
    $push_target_user_email_addresses = array_distinct($push.target.user.email_addresses)
    $push_target_user_userid = array_distinct($push.target.user.userid)
    $push_security_result_risk_reason = array_distinct($push.security_result.detection_fields["Risk Reasons"])
    $dc_push_network_session_id = count_distinct($push.network.parent_session_id)
    $auth_target_user_agent = array_distinct($auth.network.http.user_agent)
    $auth_principal_ip = array_distinct($auth.principal.ip)
    $auth_principal_ip_country = array_distinct($auth.principal.ip_geo_artifact.location.country_or_region)
    //$auth_principal_ip_state = array_distinct($auth.principal.ip_geo_artifact.location.state)
    //$auth_principal_ip_city = array_distinct($auth.principal.location.city)
    $auth_principal_user_email_addresses = array_distinct ($auth.principal.user.email_addresses)
    $auth_security_result_summary = array_distinct($auth.security_result.summary)
    $auth_target_user_email_addresses = array_distinct($auth.target.user.email_addresses)
    $auth_target_user_userid = array_distinct($auth.target.user.userid)

  condition:
    #push > 4 and $auth
}

YARA-L rule structure

Condition

Fires when $push occurs more than 4 times in the 15m window and at least one $auth event in the 15m window.

Events

$push USER_UNCATEGORIZED

  • metadata.product_event_type = "system.push.send_factor_verify_push"

$auth USER_LOGIN

  • metadata.product_event_type = "user.authentication.auth_via_mfa"
  • security_result.action = "ALLOW"

Match and correlation

Order
$push before $auth
Match key
$parent_session_id (network.parent_session_id)
Within
15m

Outcome

Outcome variables add context to a detection. When the rule generates an alert, $risk_score is displayed with it.

FieldExpression
risk_scoremax(35)
push_target_user_agentarray_distinct($push.network.http.user_agent)
push_principal_iparray_distinct($push.principal.ip)
push_principal_ip_countryarray_distinct($push.principal.ip_geo_artifact.location.country_or_region)
push_principal_ip_statearray_distinct($push.principal.ip_geo_artifact.location.state)
push_principal_user_email_addressesarray_distinct ($push.principal.user.email_addresses)
push_security_result_summaryarray_distinct($push.security_result.summary)
push_target_user_email_addressesarray_distinct($push.target.user.email_addresses)
push_target_user_useridarray_distinct($push.target.user.userid)
push_security_result_risk_reasonarray_distinct($push.security_result.detection_fields["Risk Reasons"])
dc_push_network_session_idcount_distinct($push.network.parent_session_id)
auth_target_user_agentarray_distinct($auth.network.http.user_agent)
auth_principal_iparray_distinct($auth.principal.ip)
auth_principal_ip_countryarray_distinct($auth.principal.ip_geo_artifact.location.country_or_region)
auth_principal_user_email_addressesarray_distinct ($auth.principal.user.email_addresses)
auth_security_result_summaryarray_distinct($auth.security_result.summary)
auth_target_user_email_addressesarray_distinct($auth.target.user.email_addresses)
auth_target_user_useridarray_distinct($auth.target.user.userid)