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Detection rules › YARA-L

GCP Multiple HMAC Keys Deleted

Severity
high
Type
Alert
Time window
1h
Match by
user_id
Author
Google Cloud Security
Source
github.com/chronicle/detection-rules

Detect when multiple HMAC authentication keys are deleted from GCP Storage settings.

MITRE ATT&CK coverage

TacticTechniques
ImpactT1531 Account Access Removal

Event coverage

ProviderEventTitle
GCP-storage.googleapis.comstorage-hmacKeys-deleteDelete HMAC key

Rule body yaral

/*
 * Copyright 2024 Google LLC
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     https://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

rule gcp_multiple_hmac_keys_deleted {

  meta:
    author = "Google Cloud Security"
    description = "Detect when multiple HMAC authentication keys are deleted from GCP Storage settings."
    rule_id = "mr_75b441f1-edde-4a33-bc12-06a92ccb9ba8"
    rule_name = "GCP Multiple HMAC Keys Deleted"
    mitre_attack_tactic = "Impact"
    mitre_attack_technique = "Account Access Removal"
    mitre_attack_url = "https://attack.mitre.org/techniques/T1531/"
    mitre_attack_version = "v14.1"
    type = "Alert"
    data_source = "GCP Cloud Audit"
    platform = "GCP"
    severity = "High"
    priority = "High"

  events:
    $gcp.metadata.event_type = "RESOURCE_DELETION"
    $gcp.metadata.log_type = "GCP_CLOUDAUDIT"
    $gcp.metadata.product_event_type = "storage.hmacKeys.delete"
    $gcp.target.application = "storage.googleapis.com"
    $gcp.target.user.userid = $user_id

  match:
    $user_id over 1h

  outcome:
    $risk_score = max(75)
    $mitre_attack_tactic = "Impact"
    $mitre_attack_technique = "Account Access Removal"
    $mitre_attack_technique_id = "T1531"
    $event_count = count_distinct($gcp.metadata.id)
    $network_http_user_agent = array_distinct($gcp.network.http.user_agent)
    $principal_ip = array_distinct($gcp.principal.ip)
    $principal_ip_country = array_distinct($gcp.principal.ip_geo_artifact.location.country_or_region)
    $principal_ip_state = array_distinct($gcp.principal.ip_geo_artifact.location.state)
    $principal_user_id = array_distinct($gcp.principal.user.userid)
    $principal_user_display_name = array_distinct($gcp.principal.user.user_display_name)
    $target_resource_name = array_distinct($gcp.target.resource.name)

  condition:
    #gcp >= 2
}

Detection logic

Fires when $gcp occurs at least 2 times in the 1h window.

Events

$gcp RESOURCE_DELETION

  • metadata.log_type = "GCP_CLOUDAUDIT"
  • metadata.product_event_type = "storage.hmacKeys.delete"
  • target.application = "storage.googleapis.com"

Correlation

Match key
$user_id (target.user.userid)
Within
1h

Outcome

Fields the detection emits on a match. $risk_score drives alerting; Chronicle surfaces the rest on the detection.

FieldExpression
risk_scoremax(75)
event_countcount_distinct($gcp.metadata.id)
network_http_user_agentarray_distinct($gcp.network.http.user_agent)
principal_iparray_distinct($gcp.principal.ip)
principal_ip_countryarray_distinct($gcp.principal.ip_geo_artifact.location.country_or_region)
principal_ip_statearray_distinct($gcp.principal.ip_geo_artifact.location.state)
principal_user_idarray_distinct($gcp.principal.user.userid)
principal_user_display_namearray_distinct($gcp.principal.user.user_display_name)
target_resource_namearray_distinct($gcp.target.resource.name)