name: AWS Lambda UpdateFunctionCode
id: 211b80d3-6340-4345-11ad-212bf3d0d111
version: 1
date: '2022-02-24'
author: Bhavin Patel, Splunk
type: Hunting
datamodel: []
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. 
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
  automated_detection_testing: passed
  cis20:
  - CIS 13
  confidence: 90
  context:
  - Source:Cloud Data
  - Outcome:Allowed
  - Stage:Execution
  dataset:
  - https://media.githubusercontent.com/media/splunk/attack_data/master/datasets/attack_techniques/T1204/aws_updatelambdafunctioncode/aws_cloudtrail_events.json
  impact: 70
  kill_chain_phases:
  - Actions on Objectives
  message: User $user_arn$ is attempting to update the lambda function code of $function_updated$ from this IP $src_ip$
  mitre_attack_id:
  - T1204
  nist:
  - PR.DS
  - PR.AC
  - DE.CM
  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: cloud