EC2 Route Table Modified

AnalysisType: rule
Filename: aws_ec2_route_table_modified.py
RuleID: "AWS.EC2.RouteTableModified"
DisplayName: "EC2 Route Table Modified"
Enabled: true
LogTypes:
  - AWS.CloudTrail
Tags:
  - AWS
  - Exfiltration:Exfiltration Over Alternative Protocol
Reports:
  CIS:
    - 3.13
  MITRE ATT&CK:
    - TA0010:T1048
Severity: Info
Description: An EC2 Route Table was modified.
Runbook: https://docs.runpanther.io/alert-runbooks/built-in-rules/aws-ec2-route-table-modified
Reference: https://docs.aws.amazon.com/vpc/latest/userguide/WorkWithRouteTables.html
SummaryAttributes:
  - eventName
  - userAgent
  - sourceIpAddress
  - recipientAccountId
  - p_any_aws_arns
Tests:
  - Name: Route Table 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": "CreateRoute",
        "awsRegion": "us-west-2",
        "sourceIPAddress": "111.111.111.111",
        "userAgent": "console.ec2.amazonaws.com",
        "requestParameters":
          {
            "routeTableId": "rtb-1",
            "destinationCidrBlock": "0.0.0.0/0",
            "gatewayId": "igw-1",
          },
        "responseElements": { "requestID": "1", "_return": true },
        "requestID": "1",
        "eventID": "1",
        "eventType": "AwsApiCall",
        "recipientAccountId": "123456789012",
      }
  - Name: Route Table 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": "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 Route Table
    ExpectedResult: false
    Log:
      {
        "errorCode": "Blocked",
        "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": "CreateRoute",
        "awsRegion": "us-west-2",
        "sourceIPAddress": "111.111.111.111",
        "userAgent": "console.ec2.amazonaws.com",
        "requestParameters":
          {
            "routeTableId": "rtb-1",
            "destinationCidrBlock": "0.0.0.0/0",
            "gatewayId": "igw-1",
          },
        "responseElements": { "requestID": "1", "_return": true },
        "requestID": "1",
        "eventID": "1",
        "eventType": "AwsApiCall",
        "recipientAccountId": "123456789012",
      }


# ------ paired body: aws_ec2_route_table_modified.py ------

from panther_aws_helpers import aws_cloudtrail_success, aws_rule_context

# API calls that are indicative of an EC2 Route Table modification
EC2_RT_MODIFIED_EVENTS = {
    "CreateRoute",
    "CreateRouteTable",
    "ReplaceRoute",
    "ReplaceRouteTableAssociation",
    "DeleteRouteTable",
    "DeleteRoute",
    "DisassociateRouteTable",
}


def rule(event):
    return aws_cloudtrail_success(event) and event.get("eventName") in EC2_RT_MODIFIED_EVENTS


def dedup(event):
    return event.get("recipientAccountId")


def alert_context(event):
    return aws_rule_context(event)