aws_lambda_updatefunctioncode.yml

name: AWS Lambda UpdateFunctionCode
id: 211b80d3-6340-4345-11ad-212bf3d0d111
version: 7
date: '2025-05-02'
author: Bhavin Patel, Splunk
status: production
type: Hunting
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.
data_source:
- AWS CloudTrail
search: '`cloudtrail` eventSource=lambda.amazonaws.com eventName=UpdateFunctionCode*  errorCode = success  user_type=IAMUser 
  | rename user_name as user
  | stats count min(_time) as firstTime max(_time) as lastTime by signature dest user user_agent src vendor_account vendor_region vendor_product
  | `security_content_ctime(firstTime)` | `security_content_ctime(lastTime)` |`aws_lambda_updatefunctioncode_filter`'
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.
references:
- http://detectioninthe.cloud/execution/modify_lambda_function_code/
- https://sysdig.com/blog/exploit-mitigate-aws-lambdas-mitre/
tags:
  analytic_story:
  - Suspicious Cloud User Activities
  asset_type: AWS Account
  mitre_attack_id:
  - T1204
  product:
  - Splunk Enterprise
  - Splunk Enterprise Security
  - Splunk Cloud
  security_domain: threat
tests:
- name: True Positive Test
  attack_data:
  - data: 
      https://media.githubusercontent.com/media/splunk/attack_data/master/datasets/attack_techniques/T1204/aws_updatelambdafunctioncode/aws_cloudtrail_events.json
    sourcetype: aws:cloudtrail
    source: aws_cloudtrail