AWS RDS DB Instance Made Public

[metadata]
creation_date = "2024/06/29"
integration = ["aws"]
maturity = "production"
updated_date = "2026/08/05"

[rule]
author = ["Elastic"]
description = """
Identifies the creation or modification of an Amazon RDS DB instance or cluster where the "publiclyAccessible" attribute
is set to "true". Publicly accessible RDS instances expose a network endpoint on the public internet, which may allow
unauthorized access if combined with overly permissive security groups, weak authentication, or misconfigured IAM
policies. Adversaries may enable public access on an existing instance, or create a new publicly accessible instance, to
establish persistence, move data outside of controlled network boundaries, or bypass internal access controls.
"""
false_positives = [
    """
    Public access is a common configuration used to enable access from outside a private VPC. Ensure that the instance
    should not be modified in this way before taking action.
    """,
]
from = "now-6m"
index = ["filebeat-*", "logs-aws.cloudtrail-*"]
language = "eql"
license = "Elastic License v2"
name = "AWS RDS DB Instance Made Public"
note = """## Triage and analysis

### Investigating AWS RDS DB Instance Made Public

This rule detects when an Amazon RDS DB instance or cluster is created or modified with
`publiclyAccessible=true`. While some environments operate publicly accessible RDS instances,
unexpected exposure of a database to the internet is a meaningful security risk. Adversaries who
gain access to AWS credentials may modify a DB instance’s public accessibility to exfiltrate data,
establish persistence, or bypass internal network restrictions. 

#### Possible Investigation Steps

- **Identify the actor**
  - Review `aws.cloudtrail.user_identity.arn`, `aws.cloudtrail.user_identity.type`, and `access_key_id` to determine which IAM principal made the change.
  - Determine whether the user, role, or automation service typically manages RDS configurations.

- **Examine the request parameters**
  - Review `aws.cloudtrail.request_parameters` for:
    - `publiclyAccessible=true`
    - DBInstanceIdentifier / DBClusterIdentifier
    - Additional changes included in the same modification request (e.g., master user changes, security group updates)

- **Validate the target resource**
  - Determine the sensitivity of the instance:
    - What data does it store?
    - Is it production, staging, dev, or ephemeral?
  - Confirm whether the instance was previously private.

- **Assess network exposure**
  - Check associated security groups for:
    - `0.0.0.0/0` (unrestricted ingress)
    - Unexpected IP ranges  
  - Review VPC/subnet placement to determine if the instance is reachable externally.

- **Correlate with other recent CloudTrail activity**
  - Look for related events performed by the same actor:
    - `AuthorizeSecurityGroupIngress`
    - `ModifyDBInstance`
    - IAM policy modifications enabling broader DB access
  - Look for indicators of credential misuse:
    - unusual `source.ip`
    - unusual `user_agent.original`
    - MFA not used (`session_context.mfa_authenticated=false`)

- **Validate intent with owners**
  - Contact the service or database owner to confirm whether the change was an approved part of a deployment or migration.

### False Positive Analysis

- **Expected public-access configuration**
  - Some workloads intentionally require public access (e.g., internet-facing reporting tools).
  - Validate against change management tickets, deployment pipelines, or Terraform/IaC automation logs.

### Response and Remediation

- **Containment**
  - If exposure is unauthorized:
    - Modify the instance to disable public access (`publiclyAccessible=false`).
    - Restrict the security group inbound rules immediately.
    - Snapshot the instance to preserve state if compromise is suspected.

- **Investigation**
  - Review all recent actions from the same IAM principal.
  - Check for data access patterns (CloudWatch, RDS Enhanced Monitoring, VPC Flow Logs).
  - Identify whether this exposure correlates with suspicious outbound network activity.

- **Hardening**
  - Require private-only RDS instances unless explicitly documented.
  - Enforce security group least privilege and block public DB access via:
    - AWS Config rules (`rds-instance-public-access-check`)
    - Service Control Policies (SCPs) preventing public RDS settings
  - Implement continuous monitoring for network or configuration drift.

- **Recovery**
  - Restore the database to a private subnet if necessary.
  - Rotate credentials used by the DB instance and associated applications.
  - Document the incident and update policies or IaC templates to prevent recurrence.

### Additional Information:

- **[AWS IR Playbooks](https://github.com/aws-samples/aws-incident-response-playbooks/blob/c151b0dc091755fffd4d662a8f29e2f6794da52c/playbooks/)** 
- **[AWS Customer Playbook Framework](https://github.com/aws-samples/aws-customer-playbook-framework/tree/a8c7b313636b406a375952ac00b2d68e89a991f2/docs)** 
- **Security Best Practices:** [AWS Knowledge Center – Security Best Practices](https://aws.amazon.com/premiumsupport/knowledge-center/security-best-practices/).
"""
references = [
    "https://docs.aws.amazon.com/AmazonRDS/latest/APIReference/API_ModifyDBInstance.html",
    "https://docs.aws.amazon.com/AmazonRDS/latest/UserGuide/Overview.DBInstance.Modifying.html",
    "https://cloud.hacktricks.xyz/pentesting-cloud/aws-security/aws-persistence/aws-rds-persistence#make-instance-publicly-accessible-rds-modifydbinstance",
    "https://cloud.hacktricks.xyz/pentesting-cloud/aws-security/aws-privilege-escalation/aws-rds-privesc#rds-createdbinstance",
]
risk_score = 47
rule_id = "9efb3f79-b77b-466a-9fa0-3645d22d1e7f"
severity = "medium"
tags = [
    "Domain: Cloud",
    "Platform: AWS",
    "Data Source: AWS CloudTrail",
    "Service: AWS RDS",
    "Tactic: Defense Evasion",
    "Tactic: Persistence",
    "Rule Type: Event Correlation (EQL)",
    "Resources: Investigation Guide",
]
timestamp_override = "event.ingested"
type = "eql"

query = '''
any where data_stream.dataset == "aws.cloudtrail"
    and event.provider == "rds.amazonaws.com"
    and event.outcome == "success"
    and (
        (event.action == "ModifyDBInstance" and stringContains(aws.cloudtrail.request_parameters, "publiclyAccessible=true"))
        or
        (event.action in ("CreateDBInstance", "CreateDBCluster") and stringContains(aws.cloudtrail.request_parameters, "publiclyAccessible=true"))
    )
    and not user_agent.original like~ ("*Terraform*",  "*Pulumi*")
'''


[[rule.threat]]
framework = "MITRE ATT&CK"

[[rule.threat.technique]]
id = "T1133"
name = "External Remote Services"
reference = "https://attack.mitre.org/techniques/T1133/"

[[rule.threat.technique]]
id = "T1556"
name = "Modify Authentication Process"
reference = "https://attack.mitre.org/techniques/T1556/"

[[rule.threat.technique.subtechnique]]
id = "T1556.009"
name = "Conditional Access Policies"
reference = "https://attack.mitre.org/techniques/T1556/009/"

[rule.threat.tactic]
id = "TA0003"
name = "Persistence"
reference = "https://attack.mitre.org/tactics/TA0003/"

[[rule.threat]]
framework = "MITRE ATT&CK"

[rule.threat.tactic]
id = "TA0005"
name = "Defense Evasion"
reference = "https://attack.mitre.org/tactics/TA0005/"
[rule.investigation_fields]
field_names = [
    "@timestamp",
    "user.name",
    "user_agent.original",
    "source.ip",
    "aws.cloudtrail.user_identity.arn",
    "aws.cloudtrail.user_identity.type",
    "aws.cloudtrail.user_identity.access_key_id",
    "event.action",
    "event.outcome",
    "cloud.account.id",
    "cloud.region",
    "aws.cloudtrail.request_parameters",
    "aws.cloudtrail.response_elements",
]