AWSCloudTrail - S3 bucket suspicious ransomware activity

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Id	b442b9e2-5cc4-4129-a85b-a5ef38a9e5f0
Rulename	AWSCloudTrail - S3 bucket suspicious ransomware activity
Description	Detects a ransomware-like sequence where objects are read from an S3 bucket and then overwritten using an external KMS key. This pattern can indicate malicious encryption and potential data denial in the bucket.
Severity	High
Tactics	Impact
Techniques	T1486
Required data connectors	AWS
Kind	Scheduled
Query frequency	1h
Query period	1h
Trigger threshold	0
Trigger operator	gt
Source Uri	https://github.com/Azure/Azure-Sentinel/blob/master/Solutions/Amazon Web Services/Analytic Rules/AWS_S3Ransomware.yaml
Version	1.0.2
Arm template	b442b9e2-5cc4-4129-a85b-a5ef38a9e5f0.json

KQL

let timeframe = 1h;
let lookback = 2h;
// The attacker downloads the object(s) from the compromised bucket
let GetObject = AWSCloudTrail
| where TimeGenerated >= ago(lookback)
| where EventName == "GetObject" and isempty(ErrorCode) and isempty(ErrorMessage)
| extend bucketName = tostring(parse_json(RequestParameters).bucketName), keyName = tostring(parse_json(RequestParameters).key)
| project-rename StartTime = TimeGenerated;
// Then, the attacker overwrites the same object(s) but encrypted with his own key
let PutObject = AWSCloudTrail
| where TimeGenerated >= ago(timeframe)
| where EventName == "PutObject" and isempty(ErrorCode) and isempty(ErrorMessage)
| extend bucketName = tostring(parse_json(RequestParameters).bucketName), keyName = tostring(parse_json(RequestParameters).key)
| extend kmsId = tostring(parse_json(RequestParameters).["x-amz-server-side-encryption-aws-kms-key-id"])
| where tostring(kmsId) !has tostring(RecipientAccountId) and kmsId <> "";
PutObject
| join kind=inner 
(
   GetObject
)
on $left.bucketName == $right.bucketName, $left.keyName == $right.keyName
| where TimeGenerated > StartTime
| extend UserIdentityArn = iif(isempty(UserIdentityArn), tostring(parse_json(Resources)[0].ARN), UserIdentityArn)
| extend UserName = tostring(split(UserIdentityArn, '/')[-1])
| extend AccountName = case( UserIdentityPrincipalid == "Anonymous", "Anonymous", isempty(UserIdentityUserName), UserName, UserIdentityUserName)
| extend AccountName = iif(AccountName contains "@", tostring(split(AccountName, '@', 0)[0]), AccountName),
  AccountUPNSuffix = iif(AccountName contains "@", tostring(split(AccountName, '@', 1)[0]), "")

YAML

entityMappings:
- entityType: Account
  fieldMappings:
  - identifier: Name
    columnName: AccountName
  - identifier: UPNSuffix
    columnName: AccountUPNSuffix
  - identifier: CloudAppAccountId
    columnName: RecipientAccountId
- entityType: IP
  fieldMappings:
  - identifier: Address
    columnName: SourceIpAddress
tactics:
- Impact
requiredDataConnectors:
- dataTypes:
  - AWSCloudTrail
  connectorId: AWS
alertDetailsOverride:
  alertDisplayNameFormat: AWS S3 ransomware-like overwrite activity by {{AccountName}}
  alertDescriptionFormat: Detected GetObject followed by encrypted PutObject activity in bucket {{bucketName}} from {{SourceIpAddress}} for account {{RecipientAccountId}}.
id: b442b9e2-5cc4-4129-a85b-a5ef38a9e5f0
severity: High
status: Available
customDetails:
  RecipientAccountId: RecipientAccountId
  keyName: keyName
  bucketName: bucketName
  kmsId: kmsId
query: |
  let timeframe = 1h;
  let lookback = 2h;
  // The attacker downloads the object(s) from the compromised bucket
  let GetObject = AWSCloudTrail
  | where TimeGenerated >= ago(lookback)
  | where EventName == "GetObject" and isempty(ErrorCode) and isempty(ErrorMessage)
  | extend bucketName = tostring(parse_json(RequestParameters).bucketName), keyName = tostring(parse_json(RequestParameters).key)
  | project-rename StartTime = TimeGenerated;
  // Then, the attacker overwrites the same object(s) but encrypted with his own key
  let PutObject = AWSCloudTrail
  | where TimeGenerated >= ago(timeframe)
  | where EventName == "PutObject" and isempty(ErrorCode) and isempty(ErrorMessage)
  | extend bucketName = tostring(parse_json(RequestParameters).bucketName), keyName = tostring(parse_json(RequestParameters).key)
  | extend kmsId = tostring(parse_json(RequestParameters).["x-amz-server-side-encryption-aws-kms-key-id"])
  | where tostring(kmsId) !has tostring(RecipientAccountId) and kmsId <> "";
  PutObject
  | join kind=inner 
  (
     GetObject
  )
  on $left.bucketName == $right.bucketName, $left.keyName == $right.keyName
  | where TimeGenerated > StartTime
  | extend UserIdentityArn = iif(isempty(UserIdentityArn), tostring(parse_json(Resources)[0].ARN), UserIdentityArn)
  | extend UserName = tostring(split(UserIdentityArn, '/')[-1])
  | extend AccountName = case( UserIdentityPrincipalid == "Anonymous", "Anonymous", isempty(UserIdentityUserName), UserName, UserIdentityUserName)
  | extend AccountName = iif(AccountName contains "@", tostring(split(AccountName, '@', 0)[0]), AccountName),
    AccountUPNSuffix = iif(AccountName contains "@", tostring(split(AccountName, '@', 1)[0]), "")  
OriginalUri: https://github.com/Azure/Azure-Sentinel/blob/master/Solutions/Amazon Web Services/Analytic Rules/AWS_S3Ransomware.yaml
kind: Scheduled
queryPeriod: 1h
version: 1.0.2
name: AWSCloudTrail - S3 bucket suspicious ransomware activity
queryFrequency: 1h
triggerThreshold: 0
relevantTechniques:
- T1486
description: |
  Detects a ransomware-like sequence where objects are read from an S3 bucket and then overwritten using an
  external KMS key. This pattern can indicate malicious encryption and potential data denial in the bucket.  
triggerOperator: gt

ARM