AWSCloudTrail - S3 bucket exposed via policy

Status: available
Severity: medium
Time window: 1h
Source: github.com/Azure/Azure-Sentinel

Detects S3 bucket policy updates that allow public principals without restrictive conditions. Public bucket policies can expose sensitive data and should be reviewed immediately.

MITRE ATT&CK coverage

Tactic	Techniques
Exfiltration	`T1537` Transfer Data to Cloud Account

Rules detecting the same action

Other rules on this platform that filter on the same API call or operation.

AWS S3 Bucket Policy Modified (Panther)

Rule body kusto

id: 44a5b65e-b0a9-4591-aabc-388fd92a28c4
name: AWSCloudTrail - S3 bucket exposed via policy
description: |
  Detects S3 bucket policy updates that allow public principals without restrictive conditions.
  Public bucket policies can expose sensitive data and should be reviewed immediately.
severity: Medium
status: Available
requiredDataConnectors:
  - connectorId: AWS
    dataTypes:
      - AWSCloudTrail
queryFrequency: 1h
queryPeriod: 1h
triggerOperator: gt
triggerThreshold: 0
tactics:
  - Exfiltration
relevantTechniques:
  - T1537
query: |
  AWSCloudTrail
  | where EventName == "PutBucketPolicy" and isempty(ErrorCode) and isempty(ErrorMessage)
  | extend Statement = parse_json(tostring((parse_json(RequestParameters).bucketPolicy))).Statement
  | mvexpand Statement
  | extend Action = parse_json(Statement).Action , Effect = tostring(parse_json(Statement).Effect), Resource = tostring(parse_json(Statement).Resource), Condition = tostring(parse_json(Statement).Condition), Principal_aws = tostring(parse_json(Statement).Principal.AWS), Principal = tostring(parse_json(Statement).Principal)
  | extend Action = tostring(Action)
  | where Effect =~ "Allow" and (Principal_aws == "*" or Principal == "*") and isempty(Condition)
  | 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]), "")
  | distinct TimeGenerated, EventName, SourceIpAddress, RecipientAccountId, AccountName, AccountUPNSuffix, UserIdentityArn, UserIdentityUserName
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
  UserIdentityArn: UserIdentityArn
  RecipientAccountId: RecipientAccountId
alertDetailsOverride:
  alertDisplayNameFormat: 'AWS S3 bucket policy public exposure by {{AccountName}}'
  alertDescriptionFormat: 'Detected {{EventName}} from {{SourceIpAddress}} creating public bucket policy exposure in account {{RecipientAccountId}}.'
version: 1.0.2
kind: Scheduled

Stages and Predicates

Stage 1: `source`

AWSCloudTrail

Stage 2: `where`

| where EventName == "PutBucketPolicy" and isempty(ErrorCode) and isempty(ErrorMessage)

Stage 3: `extend`

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

Stage 4: `mv-expand`

| mvexpand Statement

Stage 5: `extend`

| extend Action = parse_json(Statement).Action , Effect = tostring(parse_json(Statement).Effect), Resource = tostring(parse_json(Statement).Resource), Condition = tostring(parse_json(Statement).Condition), Principal_aws = tostring(parse_json(Statement).Principal.AWS), Principal = tostring(parse_json(Statement).Principal)

Stage 6: `extend`

| extend Action = tostring(Action)

Stage 7: `where`

| where Effect =~ "Allow" and (Principal_aws == "*" or Principal == "*") and isempty(Condition)

Stage 8: `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 9: `distinct`

| distinct TimeGenerated, EventName, SourceIpAddress, RecipientAccountId, AccountName, AccountUPNSuffix, UserIdentityArn, UserIdentityUserName

Indicators

Each row is a field, operator, and value that the rule matches. The corpus column counts how many other rules in the catalog look for the same combination: high numbers point to widely-used, community-vetted indicators. Blank or 1 shows that the indicator is specific to this rule.

Field	Kind	Values
`Condition`	is_null	(no value, null check)
`Effect`	eq	`Allow`
`ErrorCode`	is_null	(no value, null check)
`ErrorMessage`	is_null	(no value, null check)
`EventName`	eq	`PutBucketPolicy` transforms: `cased`
`Principal`	eq	`*` transforms: `cased`
`Principal_aws`	eq	`*` transforms: `cased`

Output fields

Fields the rule emits when it matches. Chronicle authors list these in the outcome block; they appear on the detection and $risk_score drives alerting. Sentinel / Defender XDR rules build them up through project / summarize / extend stages. Sentinel maps these into alert fields via entityMappings and customDetails; Defender XDR custom detections surface them as alert fields directly.

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

`j` / `k`	Scroll down / up
`d` / `u`	Half-page down / up
`gg` / `G`	Top / bottom
`h` / `l`	History back / forward
`f`	Follow link (`Shift` = new tab)
`/`	Focus search
`?`	Toggle this help
`↑` / `↓`	Navigate search results
`Enter`	Open highlighted result
`Esc`	Close results / dialog

`type:`	`events` / `rules` / `providers`
`vendor:`	`sigma` / `elastic` / `splunk` / `kusto` / `chronicle` (vendor name alone also works: `sigma:`, `kql:`, `secops:`…)
`tactic:`	TA-id, slug, or name: `credential_access`, `TA0006`
`technique:`	technique or sub-technique ID: `T1003`, `T1003.001` (alias `tech:`)
`severity:`	`critical` / `high` / `medium` / `low` / `informational` (alias `sev:`)
`risk_score`	Numeric comparison on the Elastic risk score (0 to 100): `risk_score>50`, `risk_score<=20`, `risk_score=99` (alias `risk`; Elastic rules only)
`stages:`	Rules with exactly N pipeline stages
`correlation:`	`single_event` / `sequence` / `alternatives` / `alternatives_cross_log` / `all_required` / `correlated`
`with:`	Co-occurrence event-id; stacks (`with:4624 with:4769`) to require all, while a comma list in one occurrence (`with:4624,4769`) is an either-or group. Implies multi-event
`like:`	Structural neighbors of a rule slug (equivalents + subsumption stricter / broader): `like:comsvcs_lsass_memory_dump-splunk-sysmon`
`groupby:`	Entity-grouping substring match against `group_by_keys`: `groupby:user`, `groupby:host`
`uses:`	Rules whose predicate tree touches the field (any kind, any value): `uses:CommandLine`
`excludes:`	Rules with top-level `not()` clauses on the field (FP whitelists): `excludes:ParentImage`
`field:` / `value:`	Predicate search; narrows rule cards to those with a matching leaf and drives the indicator tier. Unquoted = substring, wildcards allowed (`value:mimikatz`)
`indicator:`	Shorthand for `field:F value:V`: `indicator:Image=*\powershell.exe`
`kind:`	Filter by predicate kind. Narrows rule cards to those carrying a matching predicate leaf (`vendor:elastic kind:cidr_match`) and drives the indicator tier: `contains` / `starts_with` / `ends_with` / `regex` / `cidr` / `eq` / `in` … (operator aliases `op:`/`match:`)
`has:` / `no:`	`sample`, `field`, `notes`, `refs`, `trace`, `thirdparty`, `rule`, `pattern`, `timewindow`, `threshold`, `newterms`, `sigma`/`elastic`/`splunk`/`kusto`/`chronicle`
`-op:val`	Exclude matches; works on most operators but not `type:`/`like:`/`has:`/`no:` (use `no:<flag>` to exclude a rule flag): `tactic:execution -vendor:splunk`. Standalone `-kind:`/`-field:`/`-value:` drop every rule carrying a matching predicate leaf (`type:rules -kind:is_null`)
`field:"…"` / `value:"…"`	Quoted value = anchored exact match (also allows spaces): `value:"net user"`
`a,b`	Comma = OR inside one operator (`vendor:sigma,elastic`, `severity:high,critical`); repeating a facet merges the same way. `field:`/`value:` never split (literal commas)
`vendors:` / `stage:`	Singular and plural spellings fold to the canonical operator and value: `tactics:` = `tactic:`, `type:event` = `type:events`, `correlation:sequences` = `correlation:sequence`, `has:thresholds` = `has:threshold`
`"quoted phrase"`	Exact-match a multi-word phrase (free text)

AWSCloudTrail - S3 bucket exposed via policy

MITRE ATT&CK coverage

Rules detecting the same action

Rule body kusto

Stages and Predicates

Stage 1: `source`

Stage 2: `where`

Stage 3: `extend`

Stage 4: `mv-expand`

Stage 5: `extend`

Stage 6: `extend`

Stage 7: `where`

Stage 8: `extend` (4 consecutive steps)

Stage 9: `distinct`

Indicators

Output fields

Keyboard shortcuts

Search operators

AWSCloudTrail - S3 bucket exposed via policy

MITRE ATT&CK coverage

Rules detecting the same action

Rule body kusto

Stages and Predicates

Stage 1: source

Stage 2: where

Stage 3: extend

Stage 4: mv-expand

Stage 5: extend

Stage 6: extend

Stage 7: where

Stage 8: extend (4 consecutive steps)

Stage 9: distinct

Indicators

Output fields

Stage 1: `source`

Stage 2: `where`

Stage 3: `extend`

Stage 4: `mv-expand`

Stage 5: `extend`

Stage 6: `extend`

Stage 7: `where`

Stage 8: `extend` (4 consecutive steps)

Stage 9: `distinct`