AWS IAM Assume Role Policy Brute Force

name: AWS IAM Assume Role Policy Brute Force
id: f19e09b0-9308-11eb-b7ec-acde48001122
version: 10
creation_date: '2021-04-06'
modification_date: '2026-05-13'
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
finding:
    title: User $user$ has caused multiple failures with errorCode $errorCode$, which potentially means adversary is attempting to identify a role name.
    entity:
        field: user
        type: user
        score: 50
threat_objects:
    - field: src
      type: ip_address
analytic_story:
    - AWS IAM Privilege Escalation
asset_type: AWS Account
mitre_attack_id:
    - T1580
    - T1110
product:
    - Splunk Enterprise
    - Splunk Enterprise Security
    - Splunk Cloud
category: cloud
security_domain: access