Sensitive API Calls Via VPC Endpoint

Severity: medium
Log types: AWS.CloudTrail
Tags: AWS, VPC, CloudTrail, Network Boundary Bridging, Cloud Service Discovery, Account Manipulation, Impair Defenses
Reference: https://www.wiz.io/blog/aws-vpc-endpoint-cloudtrail
Source: github.com/panther-labs/panther-analysis

Detects sensitive or unusual API calls that might indicate lateral movement, reconnaissance, or other malicious activities through VPC Endpoints. Only available for CloudTrail, EC2, KMS, S3, and Secrets Manager services.

MITRE ATT&CK coverage

Tactic	Techniques
Persistence	`T1098` Account Manipulation
Stealth	`T1562` Impair Defenses
Defense Impairment	`T1599` Network Boundary Bridging
Discovery	`T1526` Cloud Service Discovery

Rules detecting the same action

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

AWS Discovery API Calls via CLI from a Single Resource (Elastic)
AWS S3 Bucket Enumeration or Brute Force (Elastic)
Query.EC2.CRUD.Activity.Role (Panther)
Query.EC2.CRUD.Activity.Useragent (Panther)

Rule body yaml

AnalysisType: rule
Filename: aws_vpce_sensitive_api_calls.py
RuleID: "AWS.CloudTrail.VPCE.SensitiveAPICalls"
DisplayName: "Sensitive API Calls Via VPC Endpoint"
Enabled: true
LogTypes:
  - AWS.CloudTrail
Severity: Medium
Tags:
  - AWS
  - VPC
  - CloudTrail
  - Network Boundary Bridging
  - Cloud Service Discovery
  - Account Manipulation
  - Impair Defenses
Reports:
  MITRE ATT&CK:
    - TA0007:T1526 # Cloud Service Discovery
    - TA0003:T1098 # Account Manipulation
    - TA0005:T1562 # Impair Defenses
    - TA0005:T1599 # Network Boundary Bridging
Description: Detects sensitive or unusual API calls that might indicate lateral movement, reconnaissance, or other malicious activities through VPC Endpoints. Only available for CloudTrail, EC2, KMS, S3, and Secrets Manager services.
Runbook: |
  1. Identify the principal making the sensitive API call and the specific service affected
  2. Determine if this action is expected from this principal
  3. Check if the API call is one that typically requires additional scrutiny (e.g., logging configuration changes)
  4. Investigate whether the VPC Endpoint is configured to properly restrict access
  5. Review additional API calls from the same principal for suspicious patterns
  6. If unexpected activity is confirmed, consider temporarily restricting the principal's access
  7. Document findings and take appropriate remediation steps based on investigation
Reference: https://www.wiz.io/blog/aws-vpc-endpoint-cloudtrail
SummaryAttributes:
  - userIdentity.principalId
  - userIdentity.accountId
  - sourceIPAddress
  - eventSource
  - eventName
Tests:
  - Name: CloudTrail API Call Via VPC Endpoint
    ExpectedResult: true
    Log:
      {
        "eventVersion": "1.08",
        "eventCategory": "NetworkActivity",
        "eventType": "AwsVpceEvent",
        "eventTime": "2023-03-01T00:00:00Z",
        "awsRegion": "us-east-1",
        "eventSource": "cloudtrail.amazonaws.com",
        "eventName": "UpdateTrail",
        "sourceIPAddress": "10.0.0.1",
        "userIdentity": {
          "type": "IAMUser",
          "principalId": "AROAEXAMPLE:session-name",
          "accountId": "111111111111"
        },
        "requestParameters": {
          "name": "management-events",
          "isMultiRegionTrail": false
        },
        "responseElements": null,
        "vpcEndpointId": "vpce-1234abcd",
        "vpcEndpointAccountId": "111111111111",
        "recipientAccountId": "111111111111"
      }
  - Name: Regular S3 API Call (Not Sensitive)
    ExpectedResult: false
    Log:
      {
        "eventVersion": "1.08",
        "eventCategory": "NetworkActivity",
        "eventType": "AwsVpceEvent",
        "eventTime": "2023-03-01T00:00:00Z",
        "awsRegion": "us-east-1",
        "eventSource": "s3.amazonaws.com",
        "eventName": "GetObject",
        "sourceIPAddress": "10.0.0.1",
        "userIdentity": {
          "type": "IAMUser",
          "principalId": "AROAEXAMPLE:session-name",
          "accountId": "111111111111"
        },
        "requestParameters": {
          "bucketName": "example-bucket",
          "key": "example-file.txt"
        },
        "responseElements": null,
        "vpcEndpointId": "vpce-1234abcd",
        "vpcEndpointAccountId": "111111111111",
        "recipientAccountId": "111111111111"
      }
  - Name: API Call Without VPC Endpoint
    ExpectedResult: false
    Log:
      {
        "eventVersion": "1.08",
        "eventCategory": "Management",
        "eventType": "AwsApiCall",
        "eventTime": "2023-03-01T00:00:00Z",
        "awsRegion": "us-east-1",
        "eventSource": "s3.amazonaws.com",
        "eventName": "ListAllMyBuckets",
        "sourceIPAddress": "203.0.113.1",
        "userIdentity": {
          "type": "IAMUser",
          "principalId": "AROAEXAMPLE:session-name",
          "accountId": "111111111111"
        },
        "requestParameters": {},
        "responseElements": null
      }

Detection logic

Condition

not (eventType ne "AwsVpceEvent" or eventCategory ne "NetworkActivity")
eventSource in ["ec2.amazonaws.com", "kms.amazonaws.com", "secretsmanager.amazonaws.com", "s3.amazonaws.com", "cloudtrail.amazonaws.com"]

This rule also runs imperative logic the parser cannot express as a filter; the conditions above are the structured part it could extract.

Exclusions

Top-level NOT(...) conjuncts: predicates this rule actively suppresses.

Field	Kind	Excluded values
`eventCategory`	ne	`NetworkActivity`
`eventType`	ne	`AwsVpceEvent`

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
`eventSource`	in	`cloudtrail.amazonaws.com` `ec2.amazonaws.com` `kms.amazonaws.com` `s3.amazonaws.com` `secretsmanager.amazonaws.com`

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
`eventName`
`eventSource`
`awsRegion`
`recipientAccountId`
`sourceIPAddress`
`userAgent`
`userIdentity`
`actor_user`

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`f`	Follow link (`Shift` = new tab)
`/`	Focus search
`?`	Toggle this help
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`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)