AWS IAM AccessDenied Discovery Events

SPLUNK detection rule by Michael Haag, Splunk · Apache-2.0

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.

name: AWS IAM AccessDenied Discovery Events
id: 3e1f1568-9633-11eb-a69c-acde48001122
version: 11
creation_date: '2021-04-06'
modification_date: '2026-05-13'
author: Michael Haag, 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:
    - AWS CloudTrail
search: |-
    `cloudtrail` (errorCode = "AccessDenied") user_type=IAMUser (userAgent!=*.amazonaws.com)
      | bucket _time span=1h
      | rename user_name as user
      | stats count as failures min(_time) as firstTime max(_time) as lastTime, dc(signature) as methods, dc(dest) as sources values(signature) as signature values(dest) as dest
        BY src, user, vendor_account
           vendor_region, vendor_product
      | where failures >= 5 and methods >= 1 and sources >= 1
      | `security_content_ctime(firstTime)`
      | `security_content_ctime(lastTime)`
      | `aws_iam_accessdenied_discovery_events_filter`
how_to_implement: The Splunk AWS Add-on and Splunk App for AWS is required to utilize this data. The search requires AWS CloudTrail logs.
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
      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/aws_iam_accessdenied_discovery_events.json
          sourcetype: aws:cloudtrail
          source: aws_cloudtrail
      test_type: unit

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