AWS Network ACL Overly Permissive Entry Created

Severity: medium
Log types: AWS.CloudTrail
Tags: AWS, Persistence:Account Manipulation
Reference: https://docs.aws.amazon.com/vpc/latest/userguide/vpc-network-acls.html#nacl-rules
Source: github.com/panther-labs/panther-analysis

A Network ACL entry that allows access from anywhere was added.

MITRE ATT&CK coverage

Tactic	Techniques
Persistence	`T1098` Account Manipulation

Rule body yaml

AnalysisType: rule
Filename: aws_network_acl_permissive_entry.py
RuleID: "AWS.CloudTrail.NetworkACLPermissiveEntry"
DisplayName: "AWS Network ACL Overly Permissive Entry Created"
Enabled: true
LogTypes:
  - AWS.CloudTrail
Tags:
  - AWS
  - Persistence:Account Manipulation
Severity: Medium
Reports:
  MITRE ATT&CK:
    - TA0003:T1098
Description: >
  A Network ACL entry that allows access from anywhere was added.
Runbook: >
  Remove the overly permissive Network ACL entry and add a new entry with more restrictive permissions.
Reference: https://docs.aws.amazon.com/vpc/latest/userguide/vpc-network-acls.html#nacl-rules
SummaryAttributes:
  - userAgent
  - sourceIpAddress
  - recipientAccountId
  - p_any_aws_arns
Tests:
  - Name: Overly Permissive Entry Added
    ExpectedResult: true
    Log:
      {
        "awsRegion": "us-west-2",
        "eventID": "1111",
        "eventName": "CreateNetworkAclEntry",
        "eventSource": "ec2.amazonaws.com",
        "eventTime": "2019-01-01T00:00:00Z",
        "eventType": "AwsApiCall",
        "eventVersion": "1.05",
        "recipientAccountId": "123456789012",
        "requestID": "1111",
        "requestParameters":
          {
            "aclProtocol": "6",
            "cidrBlock": "0.0.0.0/0",
            "egress": false,
            "icmpTypeCode": {},
            "networkAclId": "acl-1111",
            "portRange": { "from": 700, "to": 702 },
            "ruleAction": "allow",
            "ruleNumber": 12,
          },
        "responseElements": { "_return": true, "requestId": "1111" },
        "sourceIPAddress": "111.111.111.111",
        "userAgent": "Mozilla/2.0 (compatible; NEWT ActiveX; Win32)",
        "userIdentity":
          {
            "accessKeyId": "1111",
            "accountId": "123456789012",
            "arn": "arn:aws:sts::123456789012:assumed-role/example-role/example-user",
            "principalId": "1111",
            "sessionContext":
              {
                "attributes":
                  {
                    "creationDate": "2019-01-01T00:00:00Z",
                    "mfaAuthenticated": "true",
                  },
                "sessionIssuer":
                  {
                    "accountId": "123456789012",
                    "arn": "arn:aws:iam::123456789012:role/example-role",
                    "principalId": "1111",
                    "type": "Role",
                    "userName": "example-role",
                  },
                "webIdFederationData": {},
              },
            "type": "AssumedRole",
          },
      }
  - Name: Not Overly Permissive Entry Added
    ExpectedResult: false
    Log:
      {
        "awsRegion": "us-west-2",
        "eventID": "1111",
        "eventName": "CreateNetworkAclEntry",
        "eventSource": "ec2.amazonaws.com",
        "eventTime": "2019-01-01T00:00:00Z",
        "eventType": "AwsApiCall",
        "eventVersion": "1.05",
        "recipientAccountId": "123456789012",
        "requestID": "1111",
        "requestParameters":
          {
            "aclProtocol": "6",
            "cidrBlock": "111.111.111.111/32",
            "egress": false,
            "icmpTypeCode": {},
            "networkAclId": "acl-1111",
            "portRange": { "from": 700, "to": 702 },
            "ruleAction": "allow",
            "ruleNumber": 12,
          },
        "responseElements": { "_return": true, "requestId": "1111" },
        "sourceIPAddress": "111.111.111.111",
        "userAgent": "Mozilla/2.0 (compatible; NEWT ActiveX; Win32)",
        "userIdentity":
          {
            "accessKeyId": "1111",
            "accountId": "123456789012",
            "arn": "arn:aws:sts::123456789012:assumed-role/example-role/example-user",
            "principalId": "1111",
            "sessionContext":
              {
                "attributes":
                  {
                    "creationDate": "2019-01-01T00:00:00Z",
                    "mfaAuthenticated": "true",
                  },
                "sessionIssuer":
                  {
                    "accountId": "123456789012",
                    "arn": "arn:aws:iam::123456789012:role/example-role",
                    "principalId": "1111",
                    "type": "Role",
                    "userName": "example-role",
                  },
                "webIdFederationData": {},
              },
            "type": "AssumedRole",
          },
      }
  - Name: Error Adding Overly Permissive Entry
    ExpectedResult: false
    Log:
      {
        "awsRegion": "us-west-2",
        "errorCode": "ValidationError",
        "eventID": "1111",
        "eventName": "CreateNetworkAclEntry",
        "eventSource": "ec2.amazonaws.com",
        "eventTime": "2019-01-01T00:00:00Z",
        "eventType": "AwsApiCall",
        "eventVersion": "1.05",
        "recipientAccountId": "123456789012",
        "requestID": "1111",
        "requestParameters":
          {
            "aclProtocol": "6",
            "cidrBlock": "0.0.0.0/0",
            "egress": false,
            "icmpTypeCode": {},
            "networkAclId": "acl-1111",
            "portRange": { "from": 700, "to": 702 },
            "ruleAction": "allow",
            "ruleNumber": 12,
          },
        "responseElements": { "_return": true, "requestId": "1111" },
        "sourceIPAddress": "111.111.111.111",
        "userAgent": "Mozilla/2.0 (compatible; NEWT ActiveX; Win32)",
        "userIdentity":
          {
            "accessKeyId": "1111",
            "accountId": "123456789012",
            "arn": "arn:aws:sts::123456789012:assumed-role/example-role/example-user",
            "principalId": "1111",
            "sessionContext":
              {
                "attributes":
                  {
                    "creationDate": "2019-01-01T00:00:00Z",
                    "mfaAuthenticated": "true",
                  },
                "sessionIssuer":
                  {
                    "accountId": "123456789012",
                    "arn": "arn:aws:iam::123456789012:role/example-role",
                    "principalId": "1111",
                    "type": "Role",
                    "userName": "example-role",
                  },
                "webIdFederationData": {},
              },
            "type": "AssumedRole",
          },
      }

Detection logic

Condition

not (errorCode is_not_null or errorMessage is_not_null or eventName ne "CreateNetworkAclEntry")
requestParameters.cidrBlock eq "0.0.0.0/0"
requestParameters.ruleAction eq "allow"
requestParameters.egress eq "False"

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)
`eventName`	ne	`CreateNetworkAclEntry`

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
`requestParameters.cidrBlock`	eq	`0.0.0.0/0`
`requestParameters.egress`	eq	`False`
`requestParameters.ruleAction`	eq	`allow`

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)