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📝 AWS EC2 Security Group allows unrestricted SMTP traffic 🟢

  • Contextual name: 📝 Security Group allows unrestricted SMTP traffic 🟢
  • ID: /ce/ca/aws/ec2/security-group-allows-unrestricted-smtp-traffic
  • Located in: 📁 AWS EC2

Flags​

Our Metadata​

  • Policy Type: COMPLIANCE_POLICY
  • Policy Category:
    • SECURITY

Similar Policies​

Similar Internal Rules​

RulePoliciesFlags
✉️ dec-x-11c3009f1

Logic​

Description​

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Description​

Verify and restrict inbound Simple Mail Transfer Protocol (SMTP) traffic to AWS EC2 instances by configuring Security Groups appropriately. SMTP traffic, commonly operating on ports 25 should not be allowed from unrestricted IP ranges (0.0.0.0/0) to prevent unauthorized use of the server for email relay or other malicious activities.

Rational​

Allowing unrestricted SMTP traffic can lead to unauthorized use of your instance for email relay, making it a target for spammers and significantly increasing the risk of your IP addresses being blacklisted. This misuse can affect your reputation, disrupt legitimate communications, and violate compliance policies. By restricting SMTP access to trusted IP ranges or internal systems, you reduce these risks and maintain control over mail server usage.

Impact​

Requires proper configuration to ensure legitimate email communication is not inadvertently disrupted.

Audit​

This policy marks an EC2 Security Group as INCOMPLIANT if it contains a rule that meets all the following conditions:

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Remediation​

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Remediation​

From Command Line​

  1. Run the following command to remove or modify the unrestricted rule for SMTP access:
aws ec2 revoke-security-group-ingress \
--region {{region-name}} \
--group-id {{security-group-id}} \
--protocol {{protocol}} \
--port 25 \
--cidr {{0.0.0.0/0 or ::/0}}

  • Optionally, run the authorise-security-group-ingress command to create a new rule, specifying a trusted CIDR range instead of 0.0.0.0/0.

  1. Confirm the changes by describing the security group again and ensuring the unrestricted access rule has been removed or appropriately restricted:
aws ec2 describe-security-groups \
--region {{region-name}} \
--group-ids {{security-group-id}} \
--query 'SecurityGroups[*].IpPermissions[?FromPort==`25`].{CIDR:IpRanges[*].CidrIp,Port:FromPort}'
  1. Conduct tests to verify functionality of applications dependent on SMTP to ensure they are unaffected by the changes.

policy.yaml​

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Linked Framework Sections​

SectionSub SectionsInternal RulesPoliciesFlags
💼 APRA CPG 234 → 💼 36f network design — to ensure authorised network traffic flows and to reduce the impact of security compromises;2930
💼 APRA CPG 234 → 💼 45 An understanding of plausible worst case scenarios can help regulated entities identify and implement additional controls to prevent or reduce the impact of such scenarios. One example is malware that infects computers and encrypts data, both on the infected computer and any connected storage, including (corporate) networks and cloud storage. Such attacks reinforce the importance of protecting the backup environment in the event that the production environment is compromised. Common techniques to achieve this include network segmentation, highly restricted and segregated access controls and network traffic flow restrictions.3537
💼 AWS Foundational Security Best Practices v1.0.0 → 💼 [EC2.19] Security groups should not allow unrestricted access to ports with high risk10
💼 Cloudaware Framework → 💼 Threat Protection27
💼 FedRAMP High Security Controls → 💼 AC-3 Access Enforcement (L)(M)(H)3764
💼 FedRAMP High Security Controls → 💼 AC-4 Information Flow Enforcement (M)(H)23675
💼 FedRAMP High Security Controls → 💼 AC-4(21) Physical or Logical Separation of Information Flows (M)(H)1142
💼 FedRAMP High Security Controls → 💼 CM-2 Baseline Configuration (L)(M)(H)3124
💼 FedRAMP High Security Controls → 💼 CM-2(2) Automation Support for Accuracy and Currency (M)(H)14
💼 FedRAMP High Security Controls → 💼 CM-7 Least Functionality (L)(M)(H)31833
💼 FedRAMP High Security Controls → 💼 CM-7(1) Periodic Review (M)(H)1212
💼 FedRAMP High Security Controls → 💼 SC-7 Boundary Protection (L)(M)(H)10845
💼 FedRAMP High Security Controls → 💼 SC-7(4) External Telecommunications Services (M)(H)25
💼 FedRAMP High Security Controls → 💼 SC-7(5) Deny by Default — Allow by Exception (M)(H)18
💼 FedRAMP High Security Controls → 💼 SC-7(21) Isolation of System Components (H)19
💼 FedRAMP Low Security Controls → 💼 AC-3 Access Enforcement (L)(M)(H)64
💼 FedRAMP Low Security Controls → 💼 CM-2 Baseline Configuration (L)(M)(H)23
💼 FedRAMP Low Security Controls → 💼 CM-7 Least Functionality (L)(M)(H)29
💼 FedRAMP Low Security Controls → 💼 SC-7 Boundary Protection (L)(M)(H)30
💼 FedRAMP Moderate Security Controls → 💼 AC-3 Access Enforcement (L)(M)(H)64
💼 FedRAMP Moderate Security Controls → 💼 AC-4 Information Flow Enforcement (M)(H)160
💼 FedRAMP Moderate Security Controls → 💼 AC-4(21) Physical or Logical Separation of Information Flows (M)(H)42
💼 FedRAMP Moderate Security Controls → 💼 CM-2 Baseline Configuration (L)(M)(H)324
💼 FedRAMP Moderate Security Controls → 💼 CM-2(2) Automation Support for Accuracy and Currency (M)(H)14
💼 FedRAMP Moderate Security Controls → 💼 CM-7 Least Functionality (L)(M)(H)333
💼 FedRAMP Moderate Security Controls → 💼 CM-7(1) Periodic Review (M)(H)12
💼 FedRAMP Moderate Security Controls → 💼 SC-7 Boundary Protection (L)(M)(H)739
💼 FedRAMP Moderate Security Controls → 💼 SC-7(4) External Telecommunications Services (M)(H)25
💼 FedRAMP Moderate Security Controls → 💼 SC-7(5) Deny by Default — Allow by Exception (M)(H)18
💼 ISO/IEC 27001:2013 → 💼 A.9.1.2 Access to networks and network services1718
💼 NIST CSF v1.1 → 💼 PR.AC-4: Access permissions and authorizations are managed, incorporating the principles of least privilege and separation of duties1752
💼 NIST CSF v1.1 → 💼 PR.DS-5: Protections against data leaks are implemented4766
💼 NIST CSF v1.1 → 💼 PR.PT-3: The principle of least functionality is incorporated by configuring systems to provide only essential capabilities2130
💼 NIST CSF v2.0 → 💼 DE.CM-01: Networks and network services are monitored to find potentially adverse events115
💼 NIST CSF v2.0 → 💼 DE.CM-09: Computing hardware and software, runtime environments, and their data are monitored to find potentially adverse events134
💼 NIST CSF v2.0 → 💼 ID.AM-03: Representations of the organization's authorized network communication and internal and external network data flows are maintained45
💼 NIST CSF v2.0 → 💼 PR.AA-05: Access permissions, entitlements, and authorizations are defined in a policy, managed, enforced, and reviewed, and incorporate the principles of least privilege and separation of duties88
💼 NIST CSF v2.0 → 💼 PR.DS-01: The confidentiality, integrity, and availability of data-at-rest are protected114
💼 NIST CSF v2.0 → 💼 PR.DS-02: The confidentiality, integrity, and availability of data-in-transit are protected94
💼 NIST CSF v2.0 → 💼 PR.DS-10: The confidentiality, integrity, and availability of data-in-use are protected108
💼 NIST CSF v2.0 → 💼 PR.IR-01: Networks and environments are protected from unauthorized logical access and usage66
💼 NIST SP 800-53 Revision 5 → 💼 AC-4 Information Flow Enforcement326885
💼 NIST SP 800-53 Revision 5 → 💼 AC-4(21) Information Flow Enforcement _ Physical or Logical Separation of Information Flows3742
💼 NIST SP 800-53 Revision 5 → 💼 CA-9(1) Internal System Connections _ Compliance Checks20
💼 NIST SP 800-53 Revision 5 → 💼 CM-2 Baseline Configuration723
💼 NIST SP 800-53 Revision 5 → 💼 CM-2(2) Baseline Configuration _ Automation Support for Accuracy and Currency14
💼 NIST SP 800-53 Revision 5 → 💼 CM-7 Least Functionality923
💼 NIST SP 800-53 Revision 5 → 💼 SC-7 Boundary Protection29447
💼 NIST SP 800-53 Revision 5 → 💼 SC-7(4) Boundary Protection _ External Telecommunications Services25
💼 NIST SP 800-53 Revision 5 → 💼 SC-7(5) Boundary Protection _ Deny by Default — Allow by Exception418
💼 NIST SP 800-53 Revision 5 → 💼 SC-7(11) Boundary Protection _ Restrict Incoming Communications Traffic19
💼 NIST SP 800-53 Revision 5 → 💼 SC-7(16) Boundary Protection _ Prevent Discovery of System Components20
💼 NIST SP 800-53 Revision 5 → 💼 SC-7(21) Boundary Protection _ Isolation of System Components19
💼 PCI DSS v3.2.1 → 💼 1.1 Establish and implement firewall and router configuration standards7138
💼 PCI DSS v3.2.1 → 💼 1.1.6 Documentation of business justification and approval for use of all services, protocols, and ports allowed, including documentation of security features implemented for those protocols considered to be insecure.127
💼 PCI DSS v3.2.1 → 💼 1.2.1 Restrict inbound and outbound traffic to that which is necessary for the cardholder data environment, and specifically deny all other traffic.1035
💼 PCI DSS v4.0.1 → 💼 1.2.1 Configuration standards for NSC rulesets are defined, implemented, maintained.34
💼 PCI DSS v4.0.1 → 💼 1.2.5 All services, protocols, and ports allowed are identified, approved, and have a defined business need.27
💼 PCI DSS v4.0.1 → 💼 1.2.6 Security features are defined and implemented for all services, protocols, and ports that are in use and considered to be insecure, such that the risk is mitigated.27
💼 PCI DSS v4.0.1 → 💼 1.3.1 Inbound traffic to the CDE is restricted.35
💼 PCI DSS v4.0.1 → 💼 1.3.2 Outbound traffic from the CDE is restricted.35
💼 PCI DSS v4.0 → 💼 1.2.1 Configuration standards for NSC rulesets are defined, implemented, maintained.2434
💼 PCI DSS v4.0 → 💼 1.2.5 All services, protocols, and ports allowed are identified, approved, and have a defined business need.1527
💼 PCI DSS v4.0 → 💼 1.2.6 Security features are defined and implemented for all services, protocols, and ports that are in use and considered to be insecure, such that the risk is mitigated.627
💼 PCI DSS v4.0 → 💼 1.3.1 Inbound traffic to the CDE is restricted.735
💼 PCI DSS v4.0 → 💼 1.3.2 Outbound traffic from the CDE is restricted.35
💼 SOC 2 → 💼 CC6.1-7 Restricts Access to Information Assets1326
💼 SOC 2 → 💼 CC6.6-1 Restricts Access1619
💼 UK Cyber Essentials → 💼 1.2 Prevent access to the administrative interface from the internet3638