AWSCloudTrail - Creating keys with encrypt policy without MFA

Status: available
Severity: medium
Time window: 1d
Group by: AwsEventId
Source: github.com/Azure/Azure-Sentinel

Identifies AWS KMS key creation or policy changes that allow kms:Encrypt or kms:* to any principal. This configuration can expose encryption capability outside approved boundaries and should be investigated as overly permissive or malicious.

MITRE ATT&CK coverage

Tactic	Techniques
Impact	`T1485` Data Destruction

Telemetry coverage

Platform	Record / event type
AWS	CloudTrail event `PutKeyPolicy`: Attaches a key policy to a KMS key, replacing any existing policy and controlling who can use or manage the key.

Rules detecting the same action

These rules filter on the same operation.

Rule body

id: 454133a7-5427-4a7c-bdc4-0adfa84dda16
name: AWSCloudTrail - Creating keys with encrypt policy without MFA
description: |
  Identifies AWS KMS key creation or policy changes that allow `kms:Encrypt` or `kms:*` to any principal. This configuration can expose encryption capability outside approved boundaries and should be investigated as overly permissive or malicious.
severity: Medium
status: Available
requiredDataConnectors:
  - connectorId: AWS
    dataTypes:
      - AWSCloudTrail
queryFrequency: 1d
queryPeriod: 1d
triggerOperator: gt
triggerThreshold: 0
tactics:
  - Impact
relevantTechniques:
  - T1485
query: |
    let check_actions = AWSCloudTrail
    | where EventName in ("CreateKey", "PutKeyPolicy") and isempty(ErrorCode) and isempty(ErrorMessage)
    | extend state=parse_json(parse_json(replace_string(tostring(parse_json(RequestParameters)['policy']),'\\"','"')).['Statement'])
    | mv-expand state
    | extend Action= tostring(parse_json(state.['Action'][0])), Effect=tostring(parse_json(state.['Effect'])),
             Principal=tostring(parse_json(state.['Principal']))
    | where Action in ("kms:Encrypt", "kms:*") and (Effect == 'Allow') and (Principal has "*")
    | distinct AwsEventId;
    AWSCloudTrail
    | where EventName in ("CreateKey", "PutKeyPolicy") and isempty(ErrorCode) and isempty(ErrorMessage)
    | 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]), "")
    | join kind=inner (check_actions) on AwsEventId
    | extend timestamp = TimeGenerated
    | project-away AwsEventId1
entityMappings:
  - entityType: Account
    fieldMappings:
      - identifier: Name
        columnName: AccountName
      - identifier: UPNSuffix
        columnName: AccountUPNSuffix
      - identifier: CloudAppAccountId
        columnName: RecipientAccountId
  - entityType: IP
    fieldMappings:
      - identifier: Address
        columnName: SourceIpAddress
customDetails:
  AwsEventId: AwsEventId
  EventName: EventName
  UserIdentityArn: UserIdentityArn
alertDetailsOverride:
  alertDisplayNameFormat: 'AWS KMS key creation or policy update by {{AccountName}} without MFA'
  alertDescriptionFormat: 'KMS key creation or policy update by {{AccountName}} without MFA resulted in permissive encrypt access. AwsEventId: {{AwsEventId}}'
version: 1.0.3
kind: Scheduled

Stages and Predicates

Let binding: `check_actions` used in Stage 4

let check_actions = AWSCloudTrail
| where EventName in ("CreateKey", "PutKeyPolicy") and isempty(ErrorCode) and isempty(ErrorMessage)
| extend state=parse_json(parse_json(replace_string(tostring(parse_json(RequestParameters)['policy']),'\\"','"')).['Statement'])
| mv-expand state
| extend Action= tostring(parse_json(state.['Action'][0])), Effect=tostring(parse_json(state.['Effect'])),
         Principal=tostring(parse_json(state.['Principal']))
| where Action in ("kms:Encrypt", "kms:*") and (Effect == 'Allow') and (Principal has "*")
| distinct AwsEventId;

Stage 1: `source`

AWSCloudTrail

Stage 2: `where`

| where EventName in ("CreateKey", "PutKeyPolicy") and isempty(ErrorCode) and isempty(ErrorMessage)

Stage 3: `extend` (4 consecutive steps)

| 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]), "")

Stage 4: `join`

| join kind=inner (check_actions) on AwsEventId

Stage 5: `extend`

| extend timestamp = TimeGenerated

Stage 6: `project-away`

| project-away AwsEventId1

Indicators

These rows show field, operator, and value matches.

Field	Kind	Values	Search
`Action`	in	`kms:*` `kms:Encrypt`	`field:"Action" kind:in`
`Effect`	eq	`Allow`	`field:"Effect" kind:eq value:"Allow"`
`ErrorCode`	is_null	(no value, null check)	`field:"aws::errorCode" kind:is_null`
`ErrorMessage`	is_null	(no value, null check)	`field:"aws::errorMessage" kind:is_null`
`EventName`	in	`CreateKey` `PutKeyPolicy`	`field:"aws::eventName" kind:in`
`Principal`	match	`*` transforms: `term`	`field:"Principal" kind:match value:"*"`

Output fields

These fields are emitted when the rule matches.

Field	Source
`UserIdentityArn`	`extend`
`UserName`	`extend`
`AccountName`	`extend`
`AccountUPNSuffix`	`extend`
`timestamp`	`extend`

AWSCloudTrail - Creating keys with encrypt policy without MFA

MITRE ATT&CK coverage

Telemetry coverage

Rules detecting the same action

Rule body

Stages and Predicates

Let binding: check_actions used in Stage 4

Stage 1: source

Stage 2: where

Stage 3: extend (4 consecutive steps)

Stage 4: join

Stage 5: extend

Stage 6: project-away