Detection: AWS Bedrock Invoke Model Access Denied

Updated Date: 2024-12-05 ID: c53a8e62-f741-11ee-9f6e-acde48001122 Author: Bhavin Patel, Splunk Type: TTP Product: Splunk Enterprise Security

Description

The following analytic identifies access denied error when attempting to invoke AWS Bedrock models. It leverages AWS CloudTrail logs to detect when a user or service receives an AccessDenied error when calling the InvokeModel API. This activity is significant as it may indicate an adversary attempting to access Bedrock models with insufficient permissions after compromising credentials. If confirmed malicious, this could suggest reconnaissance activities or privilege escalation attempts targeting generative AI resources, potentially leading to data exfiltration or manipulation of model outputs.

1`cloudtrail` eventSource=bedrock.amazonaws.com eventName=InvokeModel errorCode=AccessDenied  
2| rename user_name as user  
3| stats count min(_time) as firstTime max(_time) as lastTime values(requestParameters.modelId) as modelIds by src user user_agent vendor_account vendor_product dest signature vendor_region result result_id 
4| `security_content_ctime(firstTime)`  
5| `security_content_ctime(lastTime)` 
6| `aws_bedrock_invoke_model_access_denied_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_bedrock_invoke_model_access_denied_filter search *
aws_bedrock_invoke_model_access_denied_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
T1078 Valid Accounts Defense Evasion
T1550 Use Alternate Authentication Material Initial Access
Delivery
Exploitation
Installation
DE.CM
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 Notable Yes
Rule Title %name%
Rule Description %description%
Notable Event Fields user, dest
Creates Risk Event True
This configuration file applies to all detections of type TTP. These detections will use Risk Based Alerting and generate Notable Events.

Implementation

The Splunk AWS Add-on is required to utilize this data. The search requires AWS CloudTrail logs with Bedrock service events enabled. You must install and configure the AWS App for Splunk (version 6.0.0 or later) and Splunk Add-on for AWS (version 5.1.0 or later) to collect CloudTrail logs from AWS.

Known False Positives

Legitimate users may encounter access denied errors during permission testing, role transitions, or when service permissions are being reconfigured. Access denials may also happen when automated processes are using outdated credentials or when new Bedrock features are being explored.

Associated Analytic Story

Risk Based Analytics (RBA)

Risk Message:

User $user$ access denied when attempting to invoke AWS Bedrock models from $src$

Risk Object Risk Object Type Risk Score Threat Objects
user user 64 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: 1