Detection: AWS IAM AccessDenied Discovery Events

Updated Date: 2025-05-02 ID: 3e1f1568-9633-11eb-a69c-acde48001122 Author: Michael Haag, Splunk Type: Anomaly Product: Splunk Enterprise Security

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.

1`cloudtrail` (errorCode = "AccessDenied") user_type=IAMUser (userAgent!=*.amazonaws.com) 
2| bucket _time span=1h 
3| rename user_name as user 
4| 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 
5| where failures >= 5 and methods >= 1 and sources >= 1 
6| `security_content_ctime(firstTime)` 
7| `security_content_ctime(lastTime)` 
8| `aws_iam_accessdenied_discovery_events_filter`

Data Source

Name Platform Sourcetype Source
AWS CloudTrail AWS icon AWS 'aws:cloudtrail' 'aws_cloudtrail'

Macros Used

Name Value
cloudtrail sourcetype=aws:cloudtrail
aws_iam_accessdenied_discovery_events_filter search *
aws_iam_accessdenied_discovery_events_filter is an empty macro by default. It allows the user to filter out any results (false positives) without editing the SPL.

Annotations

- MITRE ATT&CK
+ Kill Chain Phases
+ NIST
+ CIS
- Threat Actors
ID Technique Tactic
T1580 Cloud Infrastructure Discovery Discovery
Exploitation
DE.AE
CIS 10

Default Configuration

This detection is configured by default in Splunk Enterprise Security to run with the following settings:

Setting Value
Disabled true
Cron Schedule 0 * * * *
Earliest Time -70m@m
Latest Time -10m@m
Schedule Window auto
Creates Risk Event True
This configuration file applies to all detections of type anomaly. These detections will use Risk Based Alerting.

Implementation

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.

Associated Analytic Story

Risk Based Analytics (RBA)

Risk Message:

User $user$ is seen to perform excessive number of discovery related api calls- $failures$, within an hour where the access was denied.

Risk Object Risk Object Type Risk Score Threat Objects
user user 10 src

References

Detection Testing

Test Type Status Dataset Source Sourcetype
Validation ✅ Passing N/A N/A N/A
Unit ✅ Passing Dataset aws_cloudtrail aws:cloudtrail
Integration ✅ Passing Dataset aws_cloudtrail aws:cloudtrail

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: GitHub | Version: 7