[New Rule] Azure Storage Account Key Regenerated (#188)

* Create credential_access_storage_account_key_regenerated.toml

* Update rules/azure/credential_access_storage_account_key_regenerated.toml

Co-authored-by: David French <56409778+threat-punter@users.noreply.github.com>

* Update credential_access_storage_account_key_regenerated.toml

Co-authored-by: David French <56409778+threat-punter@users.noreply.github.com>

rules/azure/credential_access_storage_account_key_regenerated.toml

@@ -0,0 +1,53 @@
+[metadata]
+creation_date = "2020/08/19"
+ecs_version = ["1.6.0"]
+maturity = "production"
+updated_date = "2020/08/19"
+
+[rule]
+author = ["Elastic"]
+description = """
+Identifies a rotation to storage account access keys in Azure. Regenerating access keys can affect any applications or
+Azure services that are dependent on the storage account key. Adversaries may regenerate a key as a means of acquiring
+credentials to access systems and resources.
+"""
+false_positives = [
+    """
+    It's recommended that you rotate your access keys periodically to help keep your storage account secure. Normal key
+    rotation can be exempted from the rule. An abnormal time frame and/or a key rotation from unfamiliar users, hosts,
+    or locations should be investigated.
+    """,
+]
+from = "now-25m"
+index = ["filebeat-*"]
+language = "kuery"
+license = "Elastic License"
+name = "Azure Storage Account Key Regenerated"
+note = "The Azure Filebeat module must be enabled to use this rule."
+references = [
+    "https://docs.microsoft.com/en-us/azure/storage/common/storage-account-keys-manage?tabs=azure-portal",
+]
+risk_score = 21
+rule_id = "1e0b832e-957e-43ae-b319-db82d228c908"
+severity = "low"
+tags = ["Azure", "Elastic", "SecOps", "Continuous Monitoring", "Identity and Access"]
+type = "query"
+
+query = '''
+event.module:azure and event.dataset:azure.activitylogs and event.category:Administrative and azure.activitylogs.operation_name:MICROSOFT.STORAGE/STORAGEACCOUNTS/REGENERATEKEY/ACTION and event.outcome:Success
+'''
+
+
+[[rule.threat]]
+framework = "MITRE ATT&CK"
+[[rule.threat.technique]]
+id = "T1528"
+name = "Steal Application Access Token"
+reference = "https://attack.mitre.org/techniques/T1528/"
+
+
+[rule.threat.tactic]
+id = "TA0006"
+name = "Credential Access"
+reference = "https://attack.mitre.org/tactics/TA0006/"
+