EC2 VPC Modified

Severity: informational
Group by: recipientAccountId
Compliance: CIS 3.14
Log types: AWS.CloudTrail
Tags: AWS, Security Control, Defense Evasion:Impair Defenses
Reference: https://docs.aws.amazon.com/vpc/latest/userguide/configure-your-vpc.html
Source: github.com/panther-labs/panther-analysis

An EC2 VPC was modified.

MITRE ATT&CK coverage

Tactic	Techniques
Stealth	`T1562` Impair Defenses

Rule body yaml

AnalysisType: rule
Filename: aws_ec2_vpc_modified.py
RuleID: "AWS.EC2.VPCModified"
DisplayName: "EC2 VPC Modified"
Enabled: true
LogTypes:
  - AWS.CloudTrail
Tags:
  - AWS
  - Security Control
  - Defense Evasion:Impair Defenses
Reports:
  CIS:
    - 3.14
  MITRE ATT&CK:
    - TA0005:T1562
Severity: Info
DedupPeriodMinutes: 720 # 12 hours
Description: An EC2 VPC was modified.
Runbook: https://docs.runpanther.io/alert-runbooks/built-in-rules/aws-ec2-vpc-modified
Reference: https://docs.aws.amazon.com/vpc/latest/userguide/configure-your-vpc.html
SummaryAttributes:
  - eventName
  - userAgent
  - sourceIpAddress
  - recipientAccountId
  - p_any_aws_arns
Tests:
  - Name: VPC 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":
              {
                "sessionIssuer":
                  {
                    "type": "Role",
                    "principalId": "1111",
                    "arn": "arn:aws:iam::123456789012:role/tester",
                    "accountId": "123456789012",
                    "userName": "tester",
                  },
                "webIdFederationData": {},
                "attributes":
                  {
                    "mfaAuthenticated": "true",
                    "creationDate": "2019-01-01T00:00:00Z",
                  },
              },
          },
        "eventTime": "2019-01-01T00:00:00Z",
        "eventSource": "ec2.amazonaws.com",
        "eventName": "CreateVpc",
        "awsRegion": "us-west-2",
        "sourceIPAddress": "111.111.111.111",
        "userAgent": "console.ec2.amazonaws.com",
        "requestParameters":
          {
            "cidrBlock": "0.0.0.0/26",
            "instanceTenancy": "default",
            "amazonProvidedIpv6CidrBlock": false,
          },
        "responseElements":
          {
            "requestID": "1",
            "vpc":
              {
                "vpcId": "vpc-1",
                "state": "pending",
                "ownerId": "123456789012",
                "cidrBlock": "0.0.0.0/26",
                "cidrBlockAssociationSet":
                  {
                    "items":
                      [
                        {
                          "cidrBlock": "0.0.0.0/26",
                          "associationId": "vpc-cidr-assoc-1",
                          "cidrBlockState": { "state": "associated" },
                        },
                      ],
                  },
                "ipv6CidrBlockAssociationSet": {},
                "dhcpOptionsId": "dopt-1",
                "instanceTenancy": "default",
                "tagSet": {},
                "isDefault": false,
              },
          },
        "requestID": "1",
        "eventID": "1",
        "eventType": "AwsApiCall",
        "recipientAccountId": "123456789012",
      }
  - Name: VPC Not Modified
    ExpectedResult: false
    Log:
      {
        "eventVersion": "1.05",
        "userIdentity":
          {
            "type": "AssumedRole",
            "principalId": "1111:tester",
            "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": "DescribeVpcs",
        "awsRegion": "us-west-2",
        "sourceIPAddress": "111.111.111.111",
        "userAgent": "Mozilla",
        "requestParameters": { "vpcSet": {}, "filterSet": {} },
        "responseElements": null,
        "requestID": "1",
        "eventID": "1",
        "eventType": "AwsApiCall",
        "recipientAccountId": "123456789012",
      }
  - Name: Error Modifying VPC
    ExpectedResult: false
    Log:
      {
        "errorCode": "UnknownParameter",
        "eventVersion": "1.05",
        "userIdentity":
          {
            "type": "AssumedRole",
            "principalId": "1111:tester",
            "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": "true",
                    "creationDate": "2019-01-01T00:00:00Z",
                  },
              },
          },
        "eventTime": "2019-01-01T00:00:00Z",
        "eventSource": "ec2.amazonaws.com",
        "eventName": "CreateVpc",
        "awsRegion": "us-west-2",
        "sourceIPAddress": "111.111.111.111",
        "userAgent": "console.ec2.amazonaws.com",
        "requestParameters":
          {
            "cidrBlock": "0.0.0.0/26",
            "instanceTenancy": "default",
            "amazonProvidedIpv6CidrBlock": false,
          },
        "responseElements":
          {
            "requestID": "1",
            "vpc":
              {
                "vpcId": "vpc-1",
                "state": "pending",
                "ownerId": "123456789012",
                "cidrBlock": "0.0.0.0/26",
                "cidrBlockAssociationSet":
                  {
                    "items":
                      [
                        {
                          "cidrBlock": "0.0.0.0/26",
                          "associationId": "vpc-cidr-assoc-1",
                          "cidrBlockState": { "state": "associated" },
                        },
                      ],
                  },
                "ipv6CidrBlockAssociationSet": {},
                "dhcpOptionsId": "dopt-1",
                "instanceTenancy": "default",
                "tagSet": {},
                "isDefault": false,
              },
          },
        "requestID": "1",
        "eventID": "1",
        "eventType": "AwsApiCall",
        "recipientAccountId": "123456789012",
      }

Detection logic

Condition

not (errorCode is_not_null or errorMessage is_not_null)
eventName in ["CreateVpc", "DeleteVpc", "ModifyVpcAttribute", "AcceptVpcPeeringConnection", "CreateVpcPeeringConnection", "DeleteVpcPeeringConnection", "RejectVpcPeeringConnection", "AttachClassicLinkVpc", "DetachClassicLinkVpc", "DisableVpcClassicLink", "EnableVpcClassicLink"]

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	`AcceptVpcPeeringConnection` `AttachClassicLinkVpc` `CreateVpc` `CreateVpcPeeringConnection` `DeleteVpc` `DeleteVpcPeeringConnection` `DetachClassicLinkVpc` `DisableVpcClassicLink` `EnableVpcClassicLink` `ModifyVpcAttribute` `RejectVpcPeeringConnection`

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`

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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)