aws_lambda_updatefunctioncode.yml

name: AWS Lambda UpdateFunctionCode
id: 211b80d3-6340-4345-11ad-212bf3d0d111
version: 4
date: '2024-10-22'
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 | 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`'
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
  confidence: 90
  impact: 70
  message: User $user_arn$ is attempting to update the lambda function code of $function_updated$ from this IP $src_ip$
  mitre_attack_id:
  - T1204
  observable:
  - name: src_ip
    type: IP Address
    role:
    - Attacker
  - name: user_arn
    type: User
    role:
    - Attacker
  product:
  - Splunk Enterprise
  - Splunk Enterprise Security
  - Splunk Cloud
  required_fields:
  - _time
  - eventName
  - userAgent
  - errorCode
  risk_score: 63
  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
    update_timestamp: true