AWS VPC Default Security Group Restrictions

Severity: low
Compliance: CIS 4.3; PCI 1.2.1
Tags: AWS, Security Control, Initial Access:External Remote Services
Reference: https://docs.aws.amazon.com/vpc/latest/userguide/VPC_SecurityGroups.html
Source: github.com/panther-labs/panther-analysis

This policy validates that the default Security Group for a given AWS VPC is restricting all inbound and outbound traffic.

MITRE ATT&CK coverage

Tactic	Techniques
Initial Access	`T1133` External Remote Services

Rule body yaml

AnalysisType: policy
Filename: aws_vpc_default_security_restrictions.py
PolicyID: "AWS.VPC.DefaultSecurityGroup.Restrictions"
DisplayName: "AWS VPC Default Security Group Restrictions "
Enabled: true
ResourceTypes:
  - AWS.EC2.VPC
Tags:
  - AWS
  - Security Control
  - Initial Access:External Remote Services
Reports:
  CIS:
    - 4.3
  PCI:
    - 1.2.1
  MITRE ATT&CK:
    - TA0001:T1133
Severity: Low
Description: >
  This policy validates that the default Security Group for a given AWS VPC is restricting all inbound and outbound traffic.
Runbook: >
  https://docs.runpanther.io/alert-runbooks/built-in-policies/aws-vpc-default-security-group-restricts-all-traffic
Reference: https://docs.aws.amazon.com/vpc/latest/userguide/VPC_SecurityGroups.html
#Tests:
#  -
#    Name: Default Security Group Has IP Permissions
#    ExpectedResult: false
#    Resource:
#      {
#        "CidrBlock": "172.31.0.0/16",
#        "CidrBlockAssociationSet": [
#          {
#            "AssociationId": "vpc-cidr-assoc-112233",
#            "CidrBlock": "172.0.0.0/16",
#            "CidrBlockState": {
#              "State": "associated",
#              "StatusMessage": null
#            }
#          }
#        ],
#        "DhcpOptionsId": "dopt-1122e3344",
#        "FlowLogs": null,
#        "InstanceTenancy": "default",
#        "Ipv6CidrBlockAssociationSet": null,
#        "IsDefault": true,
#        "NetworkAcls": [
#          {
#            "Associations": [
#              {
#                "NetworkAclAssociationId": "aclassoc-1122abc444",
#                "NetworkAclId": "acl-123abc",
#                "SubnetId": "subnet-123abc"
#              },
#              {
#                "NetworkAclAssociationId": "aclassoc-123abc",
#                "NetworkAclId": "acl-1122abc",
#                "SubnetId": "subnet-112233aabb"
#              }
#            ],
#            "Entries": [
#              {
#                "CidrBlock": "0.0.0.0/0",
#                "Egress": false,
#                "IcmpTypeCode": null,
#                "Ipv6CidrBlock": null,
#                "PortRange": null,
#                "Protocol": "-1",
#                "RuleAction": "deny",
#                "RuleNumber": 12345
#              }
#            ],
#            "IsDefault": true,
#            "NetworkAclId": "acl-123aabb",
#            "OwnerId": "112233445566",
#            "Tags": null,
#            "VpcId": "vpc-1234321"
#          }
#        ],
#        "OwnerId": "112233445566",
#        "RouteTables": [
#          {
#            "Associations": [
#              {
#                "Main": true,
#                "RouteTableAssociationId": "rtbassoc-1122aa33",
#                "RouteTableId": "rtb-1122abc33",
#                "SubnetId": null
#              }
#            ],
#            "OwnerId": "112233445566",
#            "PropagatingVgws": null,
#            "RouteTableId": "rtb-11223344",
#            "Routes": [
#              {
#                "DestinationCidrBlock": "0.0.0.0/0",
#                "DestinationIpv6CidrBlock": null,
#                "DestinationPrefixListId": null,
#                "EgressOnlyInternetGatewayId": null,
#                "GatewayId": "igw-abc123",
#                "InstanceId": null,
#                "InstanceOwnerId": null,
#                "NatGatewayId": null,
#                "NetworkInterfaceId": null,
#                "Origin": "CreateRoute",
#                "State": "active",
#                "TransitGatewayId": null,
#                "VpcPeeringConnectionId": null
#              }
#            ],
#            "Tags": null,
#            "VpcId": "vpc-11223344"
#          }
#        ],
#        "SecurityGroups": [
#          {
#            "Description": "default VPC security group",
#            "GroupId": "sg-abc123",
#            "GroupName": "default",
#            "IpPermissions": [
#              {
#                "FromPort": null,
#                "IpProtocol": "-1",
#                "IpRanges": null,
#                "Ipv6Ranges": null,
#                "PrefixListIds": null,
#                "ToPort": null,
#                "UserIdGroupPairs": [
#                  {
#                    "Description": null,
#                    "GroupId": "sg-abc123",
#                    "GroupName": null,
#                    "PeeringStatus": null,
#                    "UserId": "1122334455",
#                    "VpcId": null,
#                    "VpcPeeringConnectionId": null
#                  }
#                ]
#              }
#            ],
#            "IpPermissionsEgress": [
#              {
#                "FromPort": null,
#                "IpProtocol": "-1",
#                "IpRanges": [
#                  {
#                    "CidrIp": "0.0.0.0/0",
#                    "Description": null
#                  }
#                ],
#                "Ipv6Ranges": null,
#                "PrefixListIds": null,
#                "ToPort": null,
#                "UserIdGroupPairs": null
#              }
#            ],
#            "OwnerId": "112233445566",
#            "Tags": null,
#            "VpcId": "vpc-123454321"
#          }
#        ],
#        "StaleSecurityGroups": [
#          {
#            "Description": "default VPC security group",
#            "GroupId": "sg-abc567",
#            "GroupName": "default",
#            "StaleIpPermissions": null,
#            "StaleIpPermissionsEgress": [
#              {
#                "FromPort": 5555,
#                "IpProtocol": "tcp",
#                "IpRanges": null,
#                "PrefixListIds": null,
#                "ToPort": 5555,
#                "UserIdGroupPairs": [
#                  {
#                    "Description": null,
#                    "GroupId": "sg-abc567",
#                    "GroupName": "default",
#                    "PeeringStatus": "deleted",
#                    "UserId": "123456789012",
#                    "VpcId": "vpc-abc111222333444",
#                    "VpcPeeringConnectionId": null
#                  }
#                ]
#              }
#            ],
#            "VpcId": "vpc-abc123"
#          }
#        ],
#        "State": "available",
#        "Tags": null,
#        "VpcId": "vpc-1234321"
#      }
#  -
#    Name: Default Security Group Has Inbound IP Permissions
#    ExpectedResult: false
#    Resource:
#      {
#        "CidrBlock": "172.31.0.0/16",
#        "CidrBlockAssociationSet": [
#          {
#            "AssociationId": "vpc-cidr-assoc-112233",
#            "CidrBlock": "172.0.0.0/16",
#            "CidrBlockState": {
#              "State": "associated",
#              "StatusMessage": null
#            }
#          }
#        ],
#        "DhcpOptionsId": "dopt-1122e3344",
#        "FlowLogs": null,
#        "InstanceTenancy": "default",
#        "Ipv6CidrBlockAssociationSet": null,
#        "IsDefault": true,
#        "NetworkAcls": [
#          {
#            "Associations": [
#              {
#                "NetworkAclAssociationId": "aclassoc-1122abc444",
#                "NetworkAclId": "acl-123abc",
#                "SubnetId": "subnet-123abc"
#              },
#              {
#                "NetworkAclAssociationId": "aclassoc-123abc",
#                "NetworkAclId": "acl-1122abc",
#                "SubnetId": "subnet-112233aabb"
#              }
#            ],
#            "Entries": [
#              {
#                "CidrBlock": "0.0.0.0/0",
#                "Egress": false,
#                "IcmpTypeCode": null,
#                "Ipv6CidrBlock": null,
#                "PortRange": null,
#                "Protocol": "-1",
#                "RuleAction": "deny",
#                "RuleNumber": 12345
#              }
#            ],
#            "IsDefault": true,
#            "NetworkAclId": "acl-123aabb",
#            "OwnerId": "112233445566",
#            "Tags": null,
#            "VpcId": "vpc-1234321"
#          }
#        ],
#        "OwnerId": "112233445566",
#        "RouteTables": [
#          {
#            "Associations": [
#              {
#                "Main": true,
#                "RouteTableAssociationId": "rtbassoc-1122aa33",
#                "RouteTableId": "rtb-1122abc33",
#                "SubnetId": null
#              }
#            ],
#            "OwnerId": "112233445566",
#            "PropagatingVgws": null,
#            "RouteTableId": "rtb-11223344",
#            "Routes": [
#              {
#                "DestinationCidrBlock": "0.0.0.0/0",
#                "DestinationIpv6CidrBlock": null,
#                "DestinationPrefixListId": null,
#                "EgressOnlyInternetGatewayId": null,
#                "GatewayId": "igw-abc123",
#                "InstanceId": null,
#                "InstanceOwnerId": null,
#                "NatGatewayId": null,
#                "NetworkInterfaceId": null,
#                "Origin": "CreateRoute",
#                "State": "active",
#                "TransitGatewayId": null,
#                "VpcPeeringConnectionId": null
#              }
#            ],
#            "Tags": null,
#            "VpcId": "vpc-11223344"
#          }
#        ],
#        "SecurityGroups": [
#          {
#            "Description": "default VPC security group",
#            "GroupId": "sg-abc123",
#            "GroupName": "default",
#            "IpPermissions": [
#              {
#                "FromPort": null,
#                "IpProtocol": "-1",
#                "IpRanges": null,
#                "Ipv6Ranges": null,
#                "PrefixListIds": null,
#                "ToPort": null,
#                "UserIdGroupPairs": [
#                  {
#                    "Description": null,
#                    "GroupId": "sg-abc123",
#                    "GroupName": null,
#                    "PeeringStatus": null,
#                    "UserId": "1122334455",
#                    "VpcId": null,
#                    "VpcPeeringConnectionId": null
#                  }
#                ]
#              }
#            ],
#            "IpPermissionsEgress": null,
#            "OwnerId": "112233445566",
#            "Tags": null,
#            "VpcId": "vpc-123454321"
#          }
#        ],
#        "StaleSecurityGroups": [
#          {
#            "Description": "default VPC security group",
#            "GroupId": "sg-abc567",
#            "GroupName": "default",
#            "StaleIpPermissions": null,
#            "StaleIpPermissionsEgress": [
#              {
#                "FromPort": 5555,
#                "IpProtocol": "tcp",
#                "IpRanges": null,
#                "PrefixListIds": null,
#                "ToPort": 5555,
#                "UserIdGroupPairs": [
#                  {
#                    "Description": null,
#                    "GroupId": "sg-abc567",
#                    "GroupName": "default",
#                    "PeeringStatus": "deleted",
#                    "UserId": "123456789012",
#                    "VpcId": "vpc-abc111222333444",
#                    "VpcPeeringConnectionId": null
#                  }
#                ]
#              }
#            ],
#            "VpcId": "vpc-abc123"
#          }
#        ],
#        "State": "available",
#        "Tags": null,
#        "VpcId": "vpc-1234321"
#      }
#  -
#    Name: Default Security Group Has No IP Permissions
#    ExpectedResult: true
#    Resource:
#      {
#        "CidrBlock": "172.31.0.0/16",
#        "CidrBlockAssociationSet": [
#          {
#            "AssociationId": "vpc-cidr-assoc-112233",
#            "CidrBlock": "172.0.0.0/16",
#            "CidrBlockState": {
#              "State": "associated",
#              "StatusMessage": null
#            }
#          }
#        ],
#        "DhcpOptionsId": "dopt-1122e3344",
#        "FlowLogs": null,
#        "InstanceTenancy": "default",
#        "Ipv6CidrBlockAssociationSet": null,
#        "IsDefault": true,
#        "NetworkAcls": [
#          {
#            "Associations": [
#              {
#                "NetworkAclAssociationId": "aclassoc-1122abc444",
#                "NetworkAclId": "acl-123abc",
#                "SubnetId": "subnet-123abc"
#              },
#              {
#                "NetworkAclAssociationId": "aclassoc-123abc",
#                "NetworkAclId": "acl-1122abc",
#                "SubnetId": "subnet-112233aabb"
#              }
#            ],
#            "Entries": [
#              {
#                "CidrBlock": "0.0.0.0/0",
#                "Egress": false,
#                "IcmpTypeCode": null,
#                "Ipv6CidrBlock": null,
#                "PortRange": null,
#                "Protocol": "-1",
#                "RuleAction": "deny",
#                "RuleNumber": 12345
#              }
#            ],
#            "IsDefault": true,
#            "NetworkAclId": "acl-123aabb",
#            "OwnerId": "112233445566",
#            "Tags": null,
#            "VpcId": "vpc-1234321"
#          }
#        ],
#        "OwnerId": "112233445566",
#        "RouteTables": [
#          {
#            "Associations": [
#              {
#                "Main": true,
#                "RouteTableAssociationId": "rtbassoc-1122aa33",
#                "RouteTableId": "rtb-1122abc33",
#                "SubnetId": null
#              }
#            ],
#            "OwnerId": "112233445566",
#            "PropagatingVgws": null,
#            "RouteTableId": "rtb-11223344",
#            "Routes": [
#              {
#                "DestinationCidrBlock": "0.0.0.0/0",
#                "DestinationIpv6CidrBlock": null,
#                "DestinationPrefixListId": null,
#                "EgressOnlyInternetGatewayId": null,
#                "GatewayId": "igw-abc123",
#                "InstanceId": null,
#                "InstanceOwnerId": null,
#                "NatGatewayId": null,
#                "NetworkInterfaceId": null,
#                "Origin": "CreateRoute",
#                "State": "active",
#                "TransitGatewayId": null,
#                "VpcPeeringConnectionId": null
#              }
#            ],
#            "Tags": null,
#            "VpcId": "vpc-11223344"
#          }
#        ],
#        "SecurityGroups": [
#          {
#            "Description": "default VPC security group",
#            "GroupId": "sg-abc123",
#            "GroupName": "default",
#            "IpPermissions": null,
#            "IpPermissionsEgress": null,
#            "OwnerId": "112233445566",
#            "Tags": null,
#            "VpcId": "vpc-123454321"
#          }
#        ],
#        "StaleSecurityGroups": [
#          {
#            "Description": "default VPC security group",
#            "GroupId": "sg-abc567",
#            "GroupName": "default",
#            "StaleIpPermissions": null,
#            "StaleIpPermissionsEgress": [
#              {
#                "FromPort": 5555,
#                "IpProtocol": "tcp",
#                "IpRanges": null,
#                "PrefixListIds": null,
#                "ToPort": 5555,
#                "UserIdGroupPairs": [
#                  {
#                    "Description": null,
#                    "GroupId": "sg-abc567",
#                    "GroupName": "default",
#                    "PeeringStatus": "deleted",
#                    "UserId": "123456789012",
#                    "VpcId": "vpc-abc111222333444",
#                    "VpcPeeringConnectionId": null
#                  }
#                ]
#              }
#            ],
#            "VpcId": "vpc-abc123"
#          }
#        ],
#        "State": "available",
#        "Tags": null,
#        "VpcId": "vpc-1234321"
#      }
#  -
#    Name: Default Security Group Has Outbound IP Permissions
#    ExpectedResult: false
#    Resource:
#      {
#        "CidrBlock": "172.31.0.0/16",
#        "CidrBlockAssociationSet": [
#          {
#            "AssociationId": "vpc-cidr-assoc-112233",
#            "CidrBlock": "172.0.0.0/16",
#            "CidrBlockState": {
#              "State": "associated",
#              "StatusMessage": null
#            }
#          }
#        ],
#        "DhcpOptionsId": "dopt-1122e3344",
#        "FlowLogs": null,
#        "InstanceTenancy": "default",
#        "Ipv6CidrBlockAssociationSet": null,
#        "IsDefault": true,
#        "NetworkAcls": [
#          {
#            "Associations": [
#              {
#                "NetworkAclAssociationId": "aclassoc-1122abc444",
#                "NetworkAclId": "acl-123abc",
#                "SubnetId": "subnet-123abc"
#              },
#              {
#                "NetworkAclAssociationId": "aclassoc-123abc",
#                "NetworkAclId": "acl-1122abc",
#                "SubnetId": "subnet-112233aabb"
#              }
#            ],
#            "Entries": [
#              {
#                "CidrBlock": "0.0.0.0/0",
#                "Egress": false,
#                "IcmpTypeCode": null,
#                "Ipv6CidrBlock": null,
#                "PortRange": null,
#                "Protocol": "-1",
#                "RuleAction": "deny",
#                "RuleNumber": 12345
#              }
#            ],
#            "IsDefault": true,
#            "NetworkAclId": "acl-123aabb",
#            "OwnerId": "112233445566",
#            "Tags": null,
#            "VpcId": "vpc-1234321"
#          }
#        ],
#        "OwnerId": "112233445566",
#        "RouteTables": [
#          {
#            "Associations": [
#              {
#                "Main": true,
#                "RouteTableAssociationId": "rtbassoc-1122aa33",
#                "RouteTableId": "rtb-1122abc33",
#                "SubnetId": null
#              }
#            ],
#            "OwnerId": "112233445566",
#            "PropagatingVgws": null,
#            "RouteTableId": "rtb-11223344",
#            "Routes": [
#              {
#                "DestinationCidrBlock": "0.0.0.0/0",
#                "DestinationIpv6CidrBlock": null,
#                "DestinationPrefixListId": null,
#                "EgressOnlyInternetGatewayId": null,
#                "GatewayId": "igw-abc123",
#                "InstanceId": null,
#                "InstanceOwnerId": null,
#                "NatGatewayId": null,
#                "NetworkInterfaceId": null,
#                "Origin": "CreateRoute",
#                "State": "active",
#                "TransitGatewayId": null,
#                "VpcPeeringConnectionId": null
#              }
#            ],
#            "Tags": null,
#            "VpcId": "vpc-11223344"
#          }
#        ],
#        "SecurityGroups": [
#          {
#            "Description": "default VPC security group",
#            "GroupId": "sg-abc123",
#            "GroupName": "default",
#            "IpPermissions": null,
#            "IpPermissionsEgress": [
#              {
#                "FromPort": null,
#                "IpProtocol": "-1",
#                "IpRanges": [
#                  {
#                    "CidrIp": "0.0.0.0/0",
#                    "Description": null
#                  }
#                ],
#                "Ipv6Ranges": null,
#                "PrefixListIds": null,
#                "ToPort": null,
#                "UserIdGroupPairs": null
#              }
#            ],
#            "OwnerId": "112233445566",
#            "Tags": null,
#            "VpcId": "vpc-123454321"
#          }
#        ],
#        "StaleSecurityGroups": [
#          {
#            "Description": "default VPC security group",
#            "GroupId": "sg-abc567",
#            "GroupName": "default",
#            "StaleIpPermissions": null,
#            "StaleIpPermissionsEgress": [
#              {
#                "FromPort": 5555,
#                "IpProtocol": "tcp",
#                "IpRanges": null,
#                "PrefixListIds": null,
#                "ToPort": 5555,
#                "UserIdGroupPairs": [
#                  {
#                    "Description": null,
#                    "GroupId": "sg-abc567",
#                    "GroupName": "default",
#                    "PeeringStatus": "deleted",
#                    "UserId": "123456789012",
#                    "VpcId": "vpc-abc111222333444",
#                    "VpcPeeringConnectionId": null
#                  }
#                ]
#              }
#            ],
#            "VpcId": "vpc-abc123"
#          }
#        ],
#        "State": "available",
#        "Tags": null,
#        "VpcId": "vpc-1234321"
#      }

Detection logic

Rule logic imperative Python

from panther_aws_helpers import BadLookup, resource_lookup
def policy(resource):
    default_id = f"arn:aws:ec2:{resource['Region']}:{resource['AccountId']}:security-group/{resource['DefaultSecurityGroupId']}"
    try:
        default_sg = resource_lookup(default_id)
    except BadLookup:
        return True
    return default_sg["IpPermissions"] is None and default_sg["IpPermissionsEgress"] is None

The parser cannot express this rule's logic as a field filter; the imperative Python above is the detection.

`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)

AWS VPC Default Security Group Restrictions

MITRE ATT&CK coverage

Rule body yaml

Detection logic

Rule logic imperative Python

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