AWS Lambda Public Access

Severity: high
Tags: AWS, Data Protection
Reference: https://docs.aws.amazon.com/config/latest/developerguide/lambda-function-public-access-prohibited.html
Source: github.com/panther-labs/panther-analysis

This policy ensures that the function policy attached to the Lambda resource prohibits public access

MITRE ATT&CK coverage

Tactic	Techniques
Initial Access	`T1190` Exploit Public-Facing Application

Rule body yaml

AnalysisType: policy
Filename: aws_lambda_public_access.py
PolicyID: "AWS.Lambda.PublicAccess"
DisplayName: "AWS Lambda Public Access"
Enabled: true
ResourceTypes:
  - AWS.Lambda.Function
Tags:
  - AWS
  - Data Protection
Reports:
  MITRE ATT&CK:
    - TA0001:T1190
Severity: High
Description: >
  This policy ensures that the function policy attached to the Lambda resource prohibits public access
Reference: https://docs.aws.amazon.com/config/latest/developerguide/lambda-function-public-access-prohibited.html
Tests:
  - Name: AWS Lambda Public Access
    ExpectedResult: false
    Resource:
      AccountId: "123456789"
      Arn: arn:aws:lambda:us-west-2:123456789:function:some-name
      CodeSha256: azertyuiopqsdfghjklm
      CodeSize: 1234
      Description: Some description
      Handler: some-name.lambda_handler
      LastModified: 2024-09-13T15:23:51.000+0000
      MemorySize: 128
      Name: some-name
      Policy:
        Policy: '{"Version":"2012-10-17","Id":"default","Statement":[{"Sid":"AllowExecutionFromCloudWatch","Effect":"Allow","Principal":{"AWS":"*"},"Action":"lambda:InvokeFunction","Resource":"arn:aws:lambda:us-west-2:123456789:function:some-name"}]}'
        RevisionId: 123456789-1234-1234-1234-123456789123
      Region: us-west-2
      ResourceId: arn:aws:lambda:us-west-2:123456789:function:some-name
      ResourceType: AWS.Lambda.Function
      RevisionId: 123456789-1234-1234-1234-123456789123
      Role: arn:aws:iam::123456789:role/some-name
      Timeout: 10
      Version: $LATEST
  - Name: AWS Lambda Condition for Access
    ExpectedResult: true
    Resource:
      AccountId: "123456789"
      Arn: arn:aws:lambda:us-west-2:123456789:function:some-name
      CodeSha256: azertyuiopqsdfghjklm
      CodeSize: 1234
      Description: Some description
      Handler: some-name.lambda_handler
      LastModified: 2024-09-13T15:23:51.000+0000
      MemorySize: 128
      Name: some-name
      Policy:
        Policy: '{"Version":"2012-10-17","Id":"default","Statement":[{"Sid":"AllowExecutionFromCloudWatch","Effect":"Allow","Principal":{"AWS":"*"},"Action":"lambda:InvokeFunction","Resource":"arn:aws:lambda:us-west-2:123456789:function:some-name","Condition":{"ArnLike":{"AWS:SourceArn":"arn:aws:events:us-west-2:123456789:rule/some-name"}}}]}'
        RevisionId: 123456789-1234-1234-1234-123456789123
      Region: us-west-2
      ResourceId: arn:aws:lambda:us-west-2:123456789:function:some-name
      ResourceType: AWS.Lambda.Function
      RevisionId: 123456789-1234-1234-1234-123456789123
      Role: arn:aws:iam::123456789:role/some-name
      Timeout: 10
      Version: $LATEST
  - Name: AWS Lambda Effect Not Allow
    ExpectedResult: true
    Resource:
      AccountId: "123456789"
      Arn: arn:aws:lambda:us-west-2:123456789:function:some-name
      CodeSha256: azertyuiopqsdfghjklm
      CodeSize: 1234
      Description: Some description
      Handler: some-name.lambda_handler
      LastModified: 2024-09-13T15:23:51.000+0000
      MemorySize: 128
      Name: some-name
      Policy:
        Policy: '{"Version":"2012-10-17","Id":"default","Statement":[{"Sid":"AllowExecutionFromCloudWatch","Effect":"Block","Principal":{"AWS":"*"},"Action":"lambda:InvokeFunction","Resource":"arn:aws:lambda:us-west-2:123456789:function:some-name","Condition":{"ArnLike":{"AWS:SourceArn":"arn:aws:events:us-west-2:123456789:rule/some-name"}}}]}'
        RevisionId: 123456789-1234-1234-1234-123456789123
      Region: us-west-2
      ResourceId: arn:aws:lambda:us-west-2:123456789:function:some-name
      ResourceType: AWS.Lambda.Function
      RevisionId: 123456789-1234-1234-1234-123456789123
      Role: arn:aws:iam::123456789:role/some-name
      Timeout: 10
      Version: $LATEST
  - Name: AWS Lambda Principal Specified
    ExpectedResult: true
    Resource:
      AccountId: "123456789"
      Arn: arn:aws:lambda:us-west-2:123456789:function:some-name
      CodeSha256: azertyuiopqsdfghjklm
      CodeSize: 1234
      Description: Some description
      Handler: some-name.lambda_handler
      LastModified: 2024-09-13T15:23:51.000+0000
      MemorySize: 128
      Name: some-name
      Policy:
        Policy: '{"Version":"2012-10-17","Id":"default","Statement":[{"Sid":"AllowExecutionFromCloudWatch","Effect":"Allow","Principal":{"Service":"events.amazonaws.com"},"Action":"lambda:InvokeFunction","Resource":"arn:aws:lambda:us-west-2:123456789:function:some-name","Condition":{"ArnLike":{"AWS:SourceArn":"arn:aws:events:us-west-2:123456789:rule/some-name"}}}]}'
        RevisionId: 123456789-1234-1234-1234-123456789123
      Region: us-west-2
      ResourceId: arn:aws:lambda:us-west-2:123456789:function:some-name
      ResourceType: AWS.Lambda.Function
      RevisionId: 123456789-1234-1234-1234-123456789123
      Role: arn:aws:iam::123456789:role/some-name
      Timeout: 10
      Version: $LATEST
  - Name: AWS Lambda No Policy
    ExpectedResult: true
    Resource:
      AccountId: "123456789"
      Arn: arn:aws:lambda:us-west-2:123456789:function:some-name
      CodeSha256: azertyuiopqsdfghjklm
      CodeSize: 1234
      Description: Some description
      Handler: some-name.lambda_handler
      LastModified: 2024-09-13T15:23:51.000+0000
      MemorySize: 128
      Name: some-name
      Region: us-west-2
      ResourceId: arn:aws:lambda:us-west-2:123456789:function:some-name
      ResourceType: AWS.Lambda.Function
      RevisionId: 123456789-1234-1234-1234-123456789123
      Role: arn:aws:iam::123456789:role/some-name
      Timeout: 10
      Version: $LATEST
  - Name: AWS Lambda Unauthenticated Public Access 
    ExpectedResult: false
    Resource:
      AccountId: "123456789"
      Arn: arn:aws:lambda:us-west-2:123456789:function:some-name
      CodeSha256: azertyuiopqsdfghjklm
      CodeSize: 1234
      Description: Some description
      Handler: some-name.lambda_handler
      LastModified: 2024-09-13T15:23:51.000+0000
      MemorySize: 128
      Name: some-name
      Policy:
        Policy: '{"Version":"2012-10-17","Id":"default","Statement":[{"Sid":"AllowExecutionFromCloudWatch","Effect":"Allow","Principal":{"AWS":"*"},"Action":"lambda:InvokeFunction","Resource":"arn:aws:lambda:us-west-2:123456789:function:some-name","Condition":{"StringEquals":{"lambda:FunctionUrlAuthType":"NONE"}}}]}'
        RevisionId: 123456789-1234-1234-1234-123456789123
      Region: us-west-2
      ResourceId: arn:aws:lambda:us-west-2:123456789:function:some-name
      ResourceType: AWS.Lambda.Function
      RevisionId: 123456789-1234-1234-1234-123456789123
      Role: arn:aws:iam::123456789:role/some-name
      Timeout: 10
      Version: $LATEST

Detection logic

Rule logic imperative Python

import json

from panther_base_helpers import deep_get


def policy(resource):
    json_policy = json.loads(deep_get(resource, "Policy", "Policy", default="{}"))
    if any(
        (statement.get("Principal") == "*" or deep_get(statement, "Principal", "AWS") == "*")
        and statement.get("Effect") == "Allow"
        and (
            statement.get("Condition", {}) == {}
            or deep_get(statement, "Condition", "StringEquals", "lambda:FunctionUrlAuthType")
            == "NONE"
        )
        for statement in json_policy.get("Statement", [])
    ):
        return False
    return True


def severity(resource):
    json_policy = json.loads(deep_get(resource, "Policy", "Policy", default="{}"))
    if not any(
        deep_get(statement, "Condition", "StringEquals", "lambda:FunctionUrlAuthType") == "NONE"
        for statement in json_policy.get("Statement", [])
    ):
        return "LOW"
    return "DEFAULT"

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 Lambda Public Access

MITRE ATT&CK coverage

Rule body yaml

Detection logic

Rule logic imperative Python

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