splunk-security_content/docs/_posts/2022-02-24-aws_lambda_updatefunctioncode.md

title, excerpt, categories, last_modified_at, toc, toc_label, tags

title	excerpt	categories	last_modified_at	toc	toc_label	tags
AWS Lambda UpdateFunctionCode	User Execution	Cloud	2022-02-24	true		User Execution Execution Splunk Enterprise Splunk Enterprise Security Splunk Cloud

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Description

This analytic is designed to detect IAM users attempting to update/modify AWS lambda code via the AWS CLI to gain persistence, futher access into your AWS environment and to facilitate planting backdoors. In this instance, an attacker may upload malicious code/binary to a lambda function which will be executed automatically when the funnction is triggered.

• Type: Hunting

• Product: Splunk Enterprise, Splunk Enterprise Security, Splunk Cloud

• Last Updated: 2022-02-24

• Author: Bhavin Patel, Splunk

• ID: 211b80d3-6340-4345-11ad-212bf3d0d111

Annotations

ATT&CK

ID	Technique	Tactic
T1204	User Execution	Execution

Kill Chain Phase

• Actions on Objectives

NIST

• PR.DS
• PR.AC
• DE.CM

CIS20

• CIS 13

CVE

Search

`cloudtrail` eventSource=lambda.amazonaws.com eventName=UpdateFunctionCode*  errorCode = success  user_type=IAMUser 
| 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 
|`aws_lambda_updatefunctioncode_filter`

Macros

The SPL above uses the following Macros:

• cloudtrail

Note that aws_lambda_updatefunctioncode_filter is a empty macro by default. It allows the user to filter out any results (false positives) without editing the SPL.

Required field

• _time
• eventName
• userAgent
• errorCode

How To Implement

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

RBA

Risk Score	Impact	Confidence	Message
63.0	70	90	User user_arn is attempting to update the lambda function code of function_updated from this IP src_ip

Reference

• http://detectioninthe.cloud/execution/modify_lambda_function_code/
• https://sysdig.com/blog/exploit-mitigate-aws-lambdas-mitre/

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

• https://media.githubusercontent.com/media/splunk/attack_data/master/datasets/attack_techniques/T1204/aws_updatelambdafunctioncode/aws_cloudtrail_events.json

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