ec2_instance_modified_with_previously_unseen_user.yml

name: EC2 Instance Modified With Previously Unseen User
id: 56f91724-cf3f-4666-84e1-e3712fb41e76
version: 2
date: '2018-04-09'
description: This search looks for EC2 instances being modified by users who have
  not previously modified them.
how_to_implement: You must install the AWS App for Splunk (version 5.1.0 or later)
  and Splunk Add-on for AWS (version 4.4.0 or later), then configure your CloudTrail
  inputs. This search works best when you run the "Previously Seen EC2 Launches By
  User" support search once to create a history of previously seen ARNs. To add or
  remove APIs that modify an EC2 instance, edit the macro `ec2_modification_api_calls`.
type: ESCU
references: []
author: David Dorsey, Splunk
search: '`cloudtrail` `ec2_modification_api_calls` [search `cloudtrail` `ec2_modification_api_calls`
  errorCode=success | stats earliest(_time) as firstTime latest(_time) as lastTime
  by userIdentity.arn | rename userIdentity.arn as arn | inputlookup append=t previously_seen_ec2_modifications_by_user
  | stats min(firstTime) as firstTime, max(lastTime) as lastTime by arn | outputlookup
  previously_seen_ec2_modifications_by_user | eval newUser=if(firstTime >= relative_time(now(),
  "-70m@m"), 1, 0) | where newUser=1 | `security_content_ctime(firstTime)` | `security_content_ctime(lastTime)`
  | rename arn as userIdentity.arn | table userIdentity.arn] | spath output=dest responseElements.instancesSet.items{}.instanceId
  | spath output=user userIdentity.arn | table _time, user, dest | `ec2_instance_modified_with_previously_unseen_user_filter`'
known_false_positives: It's possible that a new user will start to modify EC2 instances
  when they haven't before for any number of reasons. Verify with the user that is
  modifying instances that this is the intended behavior.
tags:
  analytics_story:
  - Unusual AWS EC2 Modifications
  cis20:
  - CIS 1
  nist:
  - ID.AM
  security_domain: endpoint
  asset_type: AWS Instance