AWSCloudTrail - Suspicious overly permissive KMS key policy created

Status: available
Severity: high
Time window: 1d
Source: github.com/Azure/Azure-Sentinel

Detects creation or update of KMS key policies that grant broad encryption permissions to all principals. Overly permissive key policies can be abused for malicious encryption operations and indicate potential account compromise or risky misconfiguration.

MITRE ATT&CK coverage

Tactic	Techniques
Impact	`T1486` Data Encrypted for Impact

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: 60dfc193-0f73-4279-b43c-110ade02b201
name: AWSCloudTrail - Suspicious overly permissive KMS key policy created
description: |
  Detects creation or update of KMS key policies that grant broad encryption permissions to all principals.
  Overly permissive key policies can be abused for malicious encryption operations and indicate potential account
  compromise or risky misconfiguration.
severity: High
status: Available
requiredDataConnectors:
  - connectorId: AWS
    dataTypes:
      - AWSCloudTrail
queryFrequency: 1d
queryPeriod: 1d
triggerOperator: gt
triggerThreshold: 0
tactics:
  - Impact
relevantTechniques:
  - T1486
query: |
    let kmsActions = dynamic(["kms:Encrypt", "kms:*"]); //Add other overly permissive APIs to this list.
    AWSCloudTrail
    | where EventName in ("CreateKey","PutKeyPolicy") and isempty(ErrorCode) and isempty(ErrorMessage)
    | extend Statement = parse_json(tostring((parse_json(RequestParameters).policy))).Statement
    | mvexpand Statement
    | extend Action = tostring(parse_json(Statement).Action), Effect = tostring(parse_json(Statement).Effect), Principal = iff(isnotempty(tostring(parse_json(Statement).Principal.AWS)),tostring(parse_json(Statement).Principal.AWS), tostring(parse_json(Statement).Principal))
    | where Effect =~ "Allow" and Action has_any (kmsActions) and Principal == "*" 
    | 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]), "")
entityMappings:
  - entityType: Account
    fieldMappings:
      - identifier: Name
        columnName: AccountName
      - identifier: UPNSuffix
        columnName: AccountUPNSuffix
      - identifier: CloudAppAccountId
        columnName: RecipientAccountId
  - entityType: IP
    fieldMappings:
      - identifier: Address
        columnName: SourceIpAddress
customDetails:
  EventName: EventName
  EventSource: EventSource
  AWSRegion: AWSRegion
  UserIdentityArn: UserIdentityArn
alertDetailsOverride:
  alertDisplayNameFormat: 'AWS overly permissive KMS key policy change by {{AccountName}}'
  alertDescriptionFormat: 'Detected {{EventName}} from {{SourceIpAddress}} creating a broadly permissive KMS policy in account {{RecipientAccountId}}.'
version: 1.0.5
kind: Scheduled

Stages and Predicates

Parameters

let kmsActions = dynamic(["kms:Encrypt", "kms:*"]);

Stage 1: `source`

AWSCloudTrail

Stage 2: `where`

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

Stage 3: `extend`

| extend Statement = parse_json(tostring((parse_json(RequestParameters).policy))).Statement

Stage 4: `mv-expand`

| mvexpand Statement

Stage 5: `extend`

| extend Action = tostring(parse_json(Statement).Action), Effect = tostring(parse_json(Statement).Effect), Principal = iff(isnotempty(tostring(parse_json(Statement).Principal.AWS)),tostring(parse_json(Statement).Principal.AWS), tostring(parse_json(Statement).Principal))

Principal =

if/* macro: isnotempty(tostring(parse_json(Statement).Principal.AWS)) */tostring(parse_json(Statement).Principal.AWS)

elsetostring(parse_json(Statement).Principal)

Stage 6: `where`

| where Effect =~ "Allow" and Action has_any (kmsActions) and Principal == "*"

Stage 7: `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]), "")

Indicators

These rows show field, operator, and value matches.

Field	Kind	Values	Search
`Action`	match	`kms:*` transforms: `term` `kms:Encrypt` transforms: `term`	`field:"Action" kind:match`
`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`	eq	`*`	`field:"Principal" kind:eq value:"*"`

Output fields

These fields are emitted when the rule matches.

Field	Source
`Statement`	`extend`
`Action`	`extend`
`Effect`	`extend`
`Principal`	`extend`
`UserIdentityArn`	`extend`
`UserName`	`extend`
`AccountName`	`extend`
`AccountUPNSuffix`	`extend`

AWSCloudTrail - Suspicious overly permissive KMS key policy created

MITRE ATT&CK coverage

Telemetry coverage

Rules detecting the same action

Rule body

Stages and Predicates

Parameters

Stage 1: source

Stage 2: where

Stage 3: extend

Stage 4: mv-expand

Stage 5: extend

Stage 6: where

Stage 7: extend (4 consecutive steps)