AWS IAM Assume Role Policy Brute Force

name: AWS IAM Assume Role Policy Brute Force
id: f19e09b0-9308-11eb-b7ec-acde48001122
version: 8
date: '2026-03-10'
author: Michael Haag, Splunk
status: production
type: TTP
description: The following analytic detects multiple failed attempts to assume an AWS IAM role, indicating a potential brute force attack. It leverages AWS CloudTrail logs to identify `MalformedPolicyDocumentException` errors with a status of `failure` and filters out legitimate AWS services. This activity is significant as repeated failures to assume roles can indicate an adversary attempting to guess role names, which is a precursor to unauthorized access. If confirmed malicious, this could lead to unauthorized access to AWS resources, potentially compromising sensitive data and services.
data_source:
    - AWS CloudTrail
search: |-
    `cloudtrail` (errorCode=MalformedPolicyDocumentException) status=failure (userAgent!=*.amazonaws.com)
      | rename user_name as user
      | stats count min(_time) as firstTime max(_time) as lastTime values(requestParameters.policyName) as policy_name
        BY src, user, vendor_account
           vendor_region, vendor_product, signature,
           dest, errorCode
      | where count >= 2
      | `security_content_ctime(firstTime)`
      | `security_content_ctime(lastTime)`
      | `aws_iam_assume_role_policy_brute_force_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. Set the `where count` greater than a value to identify suspicious activity in your environment.
known_false_positives: This detection will require tuning to provide high fidelity detection capabilties. Tune based on src addresses (corporate offices, VPN terminations) or by groups of users.
references:
    - https://www.praetorian.com/blog/aws-iam-assume-role-vulnerabilities/
    - https://rhinosecuritylabs.com/aws/assume-worst-aws-assume-role-enumeration/
    - https://www.elastic.co/guide/en/security/current/aws-iam-brute-force-of-assume-role-policy.html
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 ("$user$") starthoursago=168  | 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: $info_min_time$
      latest_offset: $info_max_time$
rba:
    message: User $user$ has caused multiple failures with errorCode $errorCode$, which potentially means adversary is attempting to identify a role name.
    risk_objects:
        - field: user
          type: user
          score: 50
    threat_objects:
        - field: src
          type: ip_address
tags:
    analytic_story:
        - AWS IAM Privilege Escalation
    asset_type: AWS Account
    mitre_attack_id:
        - T1580
        - T1110
    product:
        - Splunk Enterprise
        - Splunk Enterprise Security
        - Splunk 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_assume_role_policy_brute_force/aws_iam_assume_role_policy_brute_force.json
          sourcetype: aws:cloudtrail
          source: aws_cloudtrail