ASL AWS IAM AccessDenied Discovery Events

Status: production
Severity: low
Group by: "actor.user.uid", _time
Author: Patrick Bareiss, Splunk
Source: github.com/splunk/security_content

The following analytic identifies excessive AccessDenied events within an hour timeframe for IAM users in AWS. It leverages AWS CloudTrail logs to detect multiple failed access attempts from the same source IP and user identity. This activity is significant as it may indicate that an access key has been compromised and is being misused for unauthorized discovery actions. If confirmed malicious, this could allow attackers to gather information about the AWS environment, potentially leading to further exploitation or privilege escalation.

MITRE ATT&CK coverage

Tactic	Techniques
Discovery	`T1580` Cloud Infrastructure Discovery

Rule body splunk

name: ASL AWS IAM AccessDenied Discovery Events
id: a4f39755-b1e2-40bb-b2dc-4449c45b0bf2
version: 7
creation_date: '2022-10-04'
modification_date: '2026-05-13'
author: Patrick Bareiss, Splunk
status: production
type: Anomaly
description: The following analytic identifies excessive AccessDenied events within an hour timeframe for IAM users in AWS. It leverages AWS CloudTrail logs to detect multiple failed access attempts from the same source IP and user identity. This activity is significant as it may indicate that an access key has been compromised and is being misused for unauthorized discovery actions. If confirmed malicious, this could allow attackers to gather information about the AWS environment, potentially leading to further exploitation or privilege escalation.
data_source:
    - ASL AWS CloudTrail
search: |-
    `amazon_security_lake` api.response.error=AccessDenied OR api.response.error=OperationNotPermittedException OR api.response.error=*Unauthorized* actor.user.type=IAMUser
      | bucket _time span=1h
      | stats count as failures min(_time) as firstTime max(_time) as lastTime dc(api.operation) as dc_operation, dc(api.service.name) as dc_service values(api.operation) as api.operation values(api.service.name) as api.service.name values(http_request.user_agent) as http_request.user_agent values(src_endpoint.ip) as src_ip values(actor.user.account.uid) as actor.user.account.uid values(cloud.provider) as cloud.provider values(cloud.region) as cloud.region
        BY _time actor.user.uid
      | where failures >= 5 AND dc_operation >= 1 AND dc_service >= 1
      | rename actor.user.uid as user api.operation as action api.service.name as dest http_request.user_agent as user_agent src_endpoint.ip as src actor.user.account.uid as vendor_account cloud.provider as vendor_product cloud.region as vendor_region
      | `security_content_ctime(firstTime)`
      | `security_content_ctime(lastTime)`
      | `asl_aws_iam_accessdenied_discovery_events_filter`
how_to_implement: The detection is based on Amazon Security Lake events from Amazon Web Services (AWS), which is a centralized data lake that provides security-related data from AWS services. To use this detection, you must ingest CloudTrail logs from Amazon Security Lake into Splunk. To run this search, ensure that you ingest events using the latest version of Splunk Add-on for Amazon Web Services (https://splunkbase.splunk.com/app/1876) or the Federated Analytics App.
known_false_positives: It is possible to start this detection will need to be tuned by source IP or user. In addition, change the count values to an upper threshold to restrict false positives.
references:
    - https://aws.amazon.com/premiumsupport/knowledge-center/troubleshoot-iam-permission-errors/
drilldown_searches:
    - name: View the detection results for - "$user$"
      search: '%original_detection_search% | search  user = "$user$"'
      earliest_offset: $info_min_time$
      latest_offset: $info_max_time$
    - name: View risk events for the last 7 days for - "$user$"
      search: '| from datamodel Risk.All_Risk | search normalized_risk_object IN ("$user$") | stats count min(_time) as firstTime max(_time) as lastTime values(search_name) as "Search Name" values(risk_message) as "Risk Message" values(analyticstories) as "Analytic Stories" values(annotations._all) as "Annotations" values(annotations.mitre_attack.mitre_tactic) as "ATT&CK Tactics" by normalized_risk_object | `security_content_ctime(firstTime)` | `security_content_ctime(lastTime)`'
      earliest_offset: 7d
      latest_offset: "0"
intermediate_findings:
    entities:
        - field: user
          type: user
          score: 20
          message: User $user$ is seen to perform excessive number of discovery related api calls- $failures$, within an hour where the access was denied.
threat_objects:
    - field: src_ip
      type: ip_address
analytic_story:
    - Suspicious Cloud User Activities
asset_type: AWS Account
mitre_attack_id:
    - T1580
product:
    - Splunk Enterprise
    - Splunk Enterprise Security
    - Splunk Cloud
category: cloud
security_domain: access
tests:
    - name: True Positive Test
      attack_data:
        - data: https://media.githubusercontent.com/media/splunk/attack_data/master/datasets/attack_techniques/T1580/aws_iam_accessdenied_discovery_events/asl_ocsf_cloudtrail.json
          sourcetype: aws:asl
          source: aws_asl
      test_type: unit

Stages and Predicates

Stage 1: `search`

`amazon_security_lake` api.response.error=AccessDenied OR api.response.error=OperationNotPermittedException OR api.response.error=*Unauthorized* actor.user.type=IAMUser

Stage 2: `bucket`

| bucket _time span=1h

Stage 3: `stats`

| stats count as failures min(_time) as firstTime max(_time) as lastTime dc(api.operation) as dc_operation, dc(api.service.name) as dc_service values(api.operation) as api.operation values(api.service.name) as api.service.name values(http_request.user_agent) as http_request.user_agent values(src_endpoint.ip) as src_ip values(actor.user.account.uid) as actor.user.account.uid values(cloud.provider) as cloud.provider values(cloud.region) as cloud.region
    BY _time actor.user.uid

Stage 4: `where`

| where failures >= 5 AND dc_operation >= 1 AND dc_service >= 1

Stage 5: `rename`

| rename actor.user.uid as user api.operation as action api.service.name as dest http_request.user_agent as user_agent src_endpoint.ip as src actor.user.account.uid as vendor_account cloud.provider as vendor_product cloud.region as vendor_region

Stage 6: `search`

| `security_content_ctime(firstTime)`

Stage 7: `search`

| `security_content_ctime(lastTime)`

Stage 8: `search`

| `asl_aws_iam_accessdenied_discovery_events_filter`

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
`actor.user.type`	eq	`IAMUser`
`api.response.error`	eq	`Unauthorized` `AccessDenied` `OperationNotPermittedException`
`dc_operation`	ge	`1`
`dc_service`	ge	`1`
`failures`	ge	`5`
`sourcetype`	eq	`aws:asl`

`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)

ASL AWS IAM AccessDenied Discovery Events

MITRE ATT&CK coverage

Rule body splunk

Stages and Predicates

Stage 1: `search`

Stage 2: `bucket`

Stage 3: `stats`

Stage 4: `where`

Stage 5: `rename`

Stage 6: `search`

Stage 7: `search`

Stage 8: `search`

Indicators

Keyboard shortcuts

Search operators

ASL AWS IAM AccessDenied Discovery Events

MITRE ATT&CK coverage

Rule body splunk

Stages and Predicates

Stage 1: search

Stage 2: bucket

Stage 3: stats

Stage 4: where

Stage 5: rename

Stage 6: search

Stage 7: search

Stage 8: search

Indicators

Stage 1: `search`

Stage 2: `bucket`

Stage 3: `stats`

Stage 4: `where`

Stage 5: `rename`

Stage 6: `search`

Stage 7: `search`

Stage 8: `search`