AWSCloudTrail - EC2 Startup Shell Script Changed

Status: available
Severity: medium
Time window: 15m
Source: github.com/Azure/Azure-Sentinel

Identifies changes to the EC2 startup script. The shell script will be executed as root/SYSTEM every time the specific instances are booted up. ref : https://github.com/RhinoSecurityLabs/pacu/blob/master/pacu/modules/ec2__startup_shell_script/main.py

MITRE ATT&CK coverage

Tactic	Techniques
Execution	`T1059` Command and Scripting Interpreter

Rules detecting the same action

Other rules on this platform that filter on the same API call or operation.

AWS EC2 Startup Script Change (Panther)
AWS Lateral Movement from Kubernetes SA via AssumeRoleWithWebIdentity (Elastic)

Rule body kusto

id: f8577e4d-8481-437b-a94e-06f615985668
name: AWSCloudTrail - EC2 Startup Shell Script Changed
description: |
  Identifies changes to the EC2 startup script. The shell script will be executed as root/SYSTEM every time the specific instances are booted up. ref : https://github.com/RhinoSecurityLabs/pacu/blob/master/pacu/modules/ec2__startup_shell_script/main.py
severity: Medium
status: Available
requiredDataConnectors:
  - connectorId: AWS
    dataTypes:
      - AWSCloudTrail
queryFrequency: 15m
queryPeriod: 15m
triggerOperator: gt
triggerThreshold: 0
tactics:
  - Execution
relevantTechniques:
  - T1059
query: |
 AWSCloudTrail
 | where EventName in~ ("ModifyInstanceAttribute", "CreateLaunchTemplate")
 | extend RequestParametersJson = parse_json(RequestParameters)
 | where tostring(RequestParametersJson.userData) != ""
 | extend userData_ = tostring(RequestParametersJson.userData)
 | extend instanceId_ = tostring(RequestParametersJson.instanceId)
 | project-away SourceSystem, Category, Type, TenantId, EventVersion, SessionIssuerAccountId
 | extend UserName = substring(UserIdentityPrincipalid, indexof_regex(UserIdentityPrincipalid, ":") + 1)
 | extend Name = split(UserName,'@')[0],UpnSuffix = split(UserName,'@')[1]
 | project TimeGenerated, EventName, UserName, Name, UpnSuffix, instanceId_, AWSRegion, SourceIpAddress, EventSource, UserIdentityArn, EventTypeName
entityMappings:
  - entityType: Account
    fieldMappings:
      - identifier: Name
        columnName: Name
      - identifier: UPNSuffix
        columnName: UpnSuffix
  - entityType: IP
    fieldMappings:
      - identifier: Address
        columnName: SourceIpAddress
customDetails:
  InstanceId: instanceId_
  AWSRegion: AWSRegion
  EventName: EventName
  EventSource: EventSource
  EventType: EventTypeName
alertDetailsOverride:
  alertDisplayNameFormat: 'EC2 startup script changed on {{instanceId_}} by {{UserName}}'
  alertDescriptionFormat: 'EC2 startup script changed on {{instanceId_}} by {{UserName}} in {{AWSRegion}}.'
version: 1.0.1
kind: Scheduled

Stages and Predicates

Stage 1: `source`

AWSCloudTrail

Stage 2: `where`

| where EventName in~ ("ModifyInstanceAttribute", "CreateLaunchTemplate")

Stage 3: `extend`

| extend RequestParametersJson = parse_json(RequestParameters)

Stage 4: `where`

| where tostring(RequestParametersJson.userData) != ""

Stage 5: `extend`

| extend userData_ = tostring(RequestParametersJson.userData)

Stage 6: `extend`

| extend instanceId_ = tostring(RequestParametersJson.instanceId)

Stage 7: `project-away`

| project-away SourceSystem, Category, Type, TenantId, EventVersion, SessionIssuerAccountId

Stage 8: `extend`

| extend UserName = substring(UserIdentityPrincipalid, indexof_regex(UserIdentityPrincipalid, ":") + 1)

Stage 9: `extend`

| extend Name = split(UserName,'@')[0],UpnSuffix = split(UserName,'@')[1]

Stage 10: `project`

| project TimeGenerated, EventName, UserName, Name, UpnSuffix, instanceId_, AWSRegion, SourceIpAddress, EventSource, UserIdentityArn, EventTypeName

Indicators

Each row is a field, operator, and value that the rule matches. The corpus column counts how many other rules in the catalog look for the same combination: high numbers point to widely-used, community-vetted indicators. Blank or 1 shows that the indicator is specific to this rule.

Field	Kind	Values
`EventName`	in	`CreateLaunchTemplate` `ModifyInstanceAttribute`

Output fields

Fields the rule emits when it matches. Chronicle authors list these in the outcome block; they appear on the detection and $risk_score drives alerting. Sentinel / Defender XDR rules build them up through project / summarize / extend stages. Sentinel maps these into alert fields via entityMappings and customDetails; Defender XDR custom detections surface them as alert fields directly.

Field	Source
`AWSRegion`	`project`
`EventName`	`project`
`EventSource`	`project`
`EventTypeName`	`project`
`Name`	`project`
`SourceIpAddress`	`project`
`TimeGenerated`	`project`
`UpnSuffix`	`project`
`UserIdentityArn`	`project`
`UserName`	`project`
`instanceId_`	`project`

`j` / `k`	Scroll down / up
`d` / `u`	Half-page down / up
`gg` / `G`	Top / bottom
`h` / `l`	History back / forward
`f`	Follow link (`Shift` = new tab)
`/`	Focus search
`?`	Toggle this help
`↑` / `↓`	Navigate search results
`Enter`	Open highlighted result
`Esc`	Close results / dialog

`type:`	`events` / `rules` / `providers`
`vendor:`	`sigma` / `elastic` / `splunk` / `kusto` / `chronicle` (vendor name alone also works: `sigma:`, `kql:`, `secops:`…)
`tactic:`	TA-id, slug, or name: `credential_access`, `TA0006`
`technique:`	technique or sub-technique ID: `T1003`, `T1003.001` (alias `tech:`)
`severity:`	`critical` / `high` / `medium` / `low` / `informational` (alias `sev:`)
`risk_score`	Numeric comparison on the Elastic risk score (0 to 100): `risk_score>50`, `risk_score<=20`, `risk_score=99` (alias `risk`; Elastic rules only)
`stages:`	Rules with exactly N pipeline stages
`correlation:`	`single_event` / `sequence` / `alternatives` / `alternatives_cross_log` / `all_required` / `correlated`
`with:`	Co-occurrence event-id; stacks (`with:4624 with:4769`) to require all, while a comma list in one occurrence (`with:4624,4769`) is an either-or group. Implies multi-event
`like:`	Structural neighbors of a rule slug (equivalents + subsumption stricter / broader): `like:comsvcs_lsass_memory_dump-splunk-sysmon`
`groupby:`	Entity-grouping substring match against `group_by_keys`: `groupby:user`, `groupby:host`
`uses:`	Rules whose predicate tree touches the field (any kind, any value): `uses:CommandLine`
`excludes:`	Rules with top-level `not()` clauses on the field (FP whitelists): `excludes:ParentImage`
`field:` / `value:`	Predicate search; narrows rule cards to those with a matching leaf and drives the indicator tier. Unquoted = substring, wildcards allowed (`value:mimikatz`)
`indicator:`	Shorthand for `field:F value:V`: `indicator:Image=*\powershell.exe`
`kind:`	Filter by predicate kind. Narrows rule cards to those carrying a matching predicate leaf (`vendor:elastic kind:cidr_match`) and drives the indicator tier: `contains` / `starts_with` / `ends_with` / `regex` / `cidr` / `eq` / `in` … (operator aliases `op:`/`match:`)
`has:` / `no:`	`sample`, `field`, `notes`, `refs`, `trace`, `thirdparty`, `rule`, `pattern`, `timewindow`, `threshold`, `newterms`, `sigma`/`elastic`/`splunk`/`kusto`/`chronicle`
`-op:val`	Exclude matches; works on most operators but not `type:`/`like:`/`has:`/`no:` (use `no:<flag>` to exclude a rule flag): `tactic:execution -vendor:splunk`. Standalone `-kind:`/`-field:`/`-value:` drop every rule carrying a matching predicate leaf (`type:rules -kind:is_null`)
`field:"…"` / `value:"…"`	Quoted value = anchored exact match (also allows spaces): `value:"net user"`
`a,b`	Comma = OR inside one operator (`vendor:sigma,elastic`, `severity:high,critical`); repeating a facet merges the same way. `field:`/`value:` never split (literal commas)
`vendors:` / `stage:`	Singular and plural spellings fold to the canonical operator and value: `tactics:` = `tactic:`, `type:event` = `type:events`, `correlation:sequences` = `correlation:sequence`, `has:thresholds` = `has:threshold`
`"quoted phrase"`	Exact-match a multi-word phrase (free text)

AWSCloudTrail - EC2 Startup Shell Script Changed

MITRE ATT&CK coverage

Rules detecting the same action

Rule body kusto

Stages and Predicates

Stage 1: `source`

Stage 2: `where`

Stage 3: `extend`

Stage 4: `where`

Stage 5: `extend`

Stage 6: `extend`

Stage 7: `project-away`

Stage 8: `extend`

Stage 9: `extend`

Stage 10: `project`

Indicators

Output fields

Keyboard shortcuts

Search operators

AWSCloudTrail - EC2 Startup Shell Script Changed

MITRE ATT&CK coverage

Rules detecting the same action

Rule body kusto

Stages and Predicates

Stage 1: source

Stage 2: where

Stage 3: extend

Stage 4: where

Stage 5: extend

Stage 6: extend

Stage 7: project-away

Stage 8: extend

Stage 9: extend

Stage 10: project

Indicators

Output fields

Stage 1: `source`

Stage 2: `where`

Stage 3: `extend`

Stage 4: `where`

Stage 5: `extend`

Stage 6: `extend`

Stage 7: `project-away`

Stage 8: `extend`

Stage 9: `extend`

Stage 10: `project`