AWS IAM Assume Role Policy Brute Force
Description
The following detection identifies any malformed policy document exceptions with a status of failure
. A malformed policy document exception occurs in instances where roles are attempted to be assumed, or brute forced. In a brute force attempt, using a tool like CloudSploit or Pacu, an attempt will look like arn:aws:iam::111111111111:role/aws-service-role/rds.amazonaws.com/AWSServiceRoleForRDS
. Meaning, when an adversary is attempting to identify a role name, multiple failures will occur. This detection focuses on the errors of a remote attempt that is failing.
- Type: TTP
-
Product: Splunk Enterprise, Splunk Enterprise Security, Splunk Cloud
- Last Updated: 2021-04-01
- Author: Michael Haag, Splunk
- ID: f19e09b0-9308-11eb-b7ec-acde48001122
Annotations
ATT&CK
Kill Chain Phase
- Reconnaissance
NIST
CIS20
CVE
Search
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`cloudtrail` (errorCode=MalformedPolicyDocumentException) status=failure (userAgent!=*.amazonaws.com)
| stats count min(_time) as firstTime max(_time) as lastTime values(requestParameters.policyName) as policy_name by src eventName eventSource aws_account_id errorCode requestParameters.policyDocument userAgent eventID awsRegion userIdentity.principalId user_arn
| where count >= 2
| `security_content_ctime(firstTime)`
| `security_content_ctime(lastTime)`
| `aws_iam_assume_role_policy_brute_force_filter`
Macros
The SPL above uses the following Macros:
aws_iam_assume_role_policy_brute_force_filter is a empty macro by default. It allows the user to filter out any results (false positives) without editing the SPL.
Required fields
List of fields required to use this analytic.
- _time
- eventName
- userAgent
- errorCode
- requestParameters.policyName
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.
Associated Analytic Story
RBA
Risk Score | Impact | Confidence | Message |
---|---|---|---|
28.0 | 40 | 70 | User $user_arn$ has caused multiple failures with errorCode $errorCode$, which potentially means adversary is attempting to identify a role name. |
The Risk Score is calculated by the following formula: Risk Score = (Impact * Confidence/100). Initial Confidence and Impact is set by the analytic author.
Reference
- 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
Test Dataset
Replay any dataset to Splunk Enterprise by using our replay.py
tool or the UI.
Alternatively you can replay a dataset into a Splunk Attack Range
source | version: 1