Detection: AWS Lambda UpdateFunctionCode

Updated Date: 2024-05-13 ID: 211b80d3-6340-4345-11ad-212bf3d0d111 Author: Bhavin Patel, Splunk Type: Hunting Product: Splunk Enterprise Security

Description

The following analytic identifies IAM users attempting to update or modify AWS Lambda code via the AWS CLI. It leverages CloudTrail logs to detect successful UpdateFunctionCode events initiated by IAM users. This activity is significant as it may indicate an attempt to gain persistence, further access, or plant backdoors within your AWS environment. If confirmed malicious, an attacker could upload and execute malicious code automatically when the Lambda function is triggered, potentially compromising the integrity and security of your AWS infrastructure.

Search

1`cloudtrail` eventSource=lambda.amazonaws.com eventName=UpdateFunctionCode*  errorCode = success  user_type=IAMUser 
2| stats  count min(_time) as firstTime max(_time) as lastTime  values(requestParameters.functionName) as function_updated by src_ip user_arn user_agent user_type eventName aws_account_id 
3|`aws_lambda_updatefunctioncode_filter`

Data Source

Name	Platform	Sourcetype	Source	Supported App
AWS CloudTrail	AWS	`'aws:cloudtrail'`	`'aws_cloudtrail'`	N/A

Macros Used

Name	Value
cloudtrail	`sourcetype=aws:cloudtrail`
aws_lambda_updatefunctioncode_filter	`search *`

aws_lambda_updatefunctioncode_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
T1204	User Execution	Execution

KillChainPhase.INSTALLATION

NistCategory.DE_AE

Cis18Value.CIS_10

LAPSUS$

Scattered Spider

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	False

This configuration file applies to all detections of type hunting.

Implementation

You must install Splunk AWS Add on and enable Cloudtrail logs in your AWS Environment.

Known False Positives

While this search has no known false positives, it is possible that an AWS admin or an autorized IAM user has updated the lambda fuction code legitimately.

Associated Analytic Story

Suspicious Cloud User Activities

Risk Based Analytics (RBA)

Risk Message	Risk Score	Impact	Confidence
User $user_arn$ is attempting to update the lambda function code of $function_updated$ from this IP $src_ip$	63	70	90

The Risk Score is calculated by the following formula: Risk Score = (Impact * Confidence/100). Initial Confidence and Impact is set by the analytic author.

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: 2