EC2 Network Gateway Modified

Severity: informational
Group by: recipientAccountId
Compliance: CIS 3.12
Log types: AWS.CloudTrail
Tags: AWS, Security Control, Defense Evasion:Impair Defenses
Reference: https://docs.aws.amazon.com/vpc/latest/userguide/VPC_Internet_Gateway.html
Source: github.com/panther-labs/panther-analysis

An EC2 Network Gateway was modified.

MITRE ATT&CK coverage

Tactic	Techniques
Stealth	`T1562` Impair Defenses

Rules detecting the same action

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

AWSCloudTrail - Changes to Amazon VPC settings (Kusto)

Rule body yaml

AnalysisType: rule
Filename: aws_ec2_gateway_modified.py
RuleID: "AWS.EC2.GatewayModified"
DisplayName: "EC2 Network Gateway Modified"
Enabled: true
LogTypes:
  - AWS.CloudTrail
Tags:
  - AWS
  - Security Control
  - Defense Evasion:Impair Defenses
Reports:
  CIS:
    - 3.12
  MITRE ATT&CK:
    - TA0005:T1562
Severity: Info
Description: An EC2 Network Gateway was modified.
Runbook: https://docs.runpanther.io/alert-runbooks/built-in-rules/aws-ec2-gateway-modified
Reference: https://docs.aws.amazon.com/vpc/latest/userguide/VPC_Internet_Gateway.html
SummaryAttributes:
  - eventName
  - userAgent
  - sourceIpAddress
  - recipientAccountId
  - p_any_aws_arns
Tests:
  - Name: Network Gateway Modified
    ExpectedResult: true
    Log:
      {
        "eventVersion": "1.05",
        "userIdentity":
          {
            "type": "AssumedRole",
            "principalId": "1111:tester",
            "arn": "arn:aws:sts::123456789012:assumed-role/tester",
            "accountId": "123456789012",
            "accessKeyId": "1",
            "sessionContext":
              {
                "attributes":
                  {
                    "mfaAuthenticated": "true",
                    "creationDate": "2019-01-01T00:00:00Z",
                  },
                "sessionIssuer":
                  {
                    "type": "Role",
                    "principalId": "1111",
                    "arn": "arn:aws:iam::123456789012:role/tester",
                    "accountId": "123456789012",
                    "userName": "tester",
                  },
              },
          },
        "eventTime": "2019-01-01T00:00:00Z",
        "eventSource": "ec2.amazonaws.com",
        "eventName": "AttachInternetGateway",
        "awsRegion": "us-west-2",
        "sourceIPAddress": "111.111.111.111",
        "userAgent": "console.ec2.amazonaws.com",
        "requestParameters": { "internetGatewayId": "igw-1", "vpcId": "vpc-1" },
        "responseElements": { "requestID": "1", "_return": true },
        "requestID": "1",
        "eventID": "1",
        "eventType": "AwsApiCall",
        "recipientAccountId": "123456789012",
      }
  - Name: Network Gateway Not Modified
    ExpectedResult: false
    Log:
      {
        "eventVersion": "1.05",
        "userIdentity":
          {
            "type": "AssumedRole",
            "principalId": "1111:2222",
            "arn": "arn:aws:sts::123456789012:assumed-role/tester",
            "accountId": "123456789012",
            "accessKeyId": "1",
            "sessionContext":
              {
                "sessionIssuer":
                  {
                    "type": "Role",
                    "principalId": "1111",
                    "arn": "arn:aws:iam::123456789012:role/tester",
                    "accountId": "123456789012",
                    "userName": "tester",
                  },
                "webIdFederationData": {},
                "attributes":
                  {
                    "mfaAuthenticated": "false",
                    "creationDate": "2019-01-01T00:00:00Z",
                  },
              },
          },
        "eventTime": "2019-01-01T00:00:00Z",
        "eventSource": "ec2.amazonaws.com",
        "eventName": "DescribeRouteTables",
        "awsRegion": "us-west-2",
        "sourceIPAddress": "111.111.111.111",
        "userAgent": "Mozilla",
        "requestParameters":
          {
            "routeTableIdSet": {},
            "filterSet":
              {
                "items":
                  [
                    {
                      "name": "resource-id",
                      "valueSet": { "items": [{ "value": "vpc-1" }] },
                    },
                  ],
              },
          },
        "responseElements": null,
        "requestID": "1",
        "eventID": "1",
        "eventType": "AwsApiCall",
        "recipientAccountId": "123456789012",
      }
  - Name: Error Modifying Network Gateway
    ExpectedResult: false
    Log:
      {
        "errorCode": "RequestExpired",
        "eventVersion": "1.05",
        "userIdentity":
          {
            "type": "AssumedRole",
            "principalId": "1111:tester",
            "arn": "arn:aws:sts::123456789012:assumed-role/tester",
            "accountId": "123456789012",
            "accessKeyId": "1",
            "sessionContext":
              {
                "attributes":
                  {
                    "mfaAuthenticated": "true",
                    "creationDate": "2019-01-01T00:00:00Z",
                  },
                "sessionIssuer":
                  {
                    "type": "Role",
                    "principalId": "1111",
                    "arn": "arn:aws:iam::123456789012:role/tester",
                    "accountId": "123456789012",
                    "userName": "tester",
                  },
              },
          },
        "eventTime": "2019-01-01T00:00:00Z",
        "eventSource": "ec2.amazonaws.com",
        "eventName": "AttachInternetGateway",
        "awsRegion": "us-west-2",
        "sourceIPAddress": "111.111.111.111",
        "userAgent": "console.ec2.amazonaws.com",
        "requestParameters": { "internetGatewayId": "igw-1", "vpcId": "vpc-1" },
        "responseElements": { "requestID": "1", "_return": true },
        "requestID": "1",
        "eventID": "1",
        "eventType": "AwsApiCall",
        "recipientAccountId": "123456789012",
      }

Detection logic

Condition

not (errorCode is_not_null or errorMessage is_not_null)
eventName in ["CreateCustomerGateway", "DeleteCustomerGateway", "AttachInternetGateway", "CreateInternetGateway", "DeleteInternetGateway", "DetachInternetGateway"]

Exclusions

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

Field	Kind	Excluded values
`errorCode`	is_not_null	(no value, null check)
`errorMessage`	is_not_null	(no value, null check)

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	`AttachInternetGateway` `CreateCustomerGateway` `CreateInternetGateway` `DeleteCustomerGateway` `DeleteInternetGateway` `DetachInternetGateway`

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`

`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)