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🛡️ AWS EC2 Security Group allows unrestricted Telnet traffic🟢

  • Contextual name: 🛡️ Security Group allows unrestricted Telnet traffic🟢
  • ID: /ce/ca/aws/ec2/security-group-allows-unrestricted-telnet-traffic
  • Tags:
  • Policy Type: COMPLIANCE_POLICY
  • Policy Categories: SECURITY

Logic​

Similar Policies​

Description​

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Description​

Verify that Telnet traffic to AWS EC2 instances is restricted. The Telnet protocol, operating on port 23, should not be open to all IP ranges (0.0.0.0/0) due to its lack of encryption and inherent security vulnerabilities.

Rational​

Telnet transmits data, including credentials, in plaintext, making it highly susceptible to interception and exploitation by malicious actors. Allowing unrestricted Telnet access exposes instances to potential unauthorized access, data compromise, and increased vulnerability to man-in-the-middle attacks. By restricting Telnet traffic to trusted sources, you mitigate these risks and improve the overall security posture of your AWS environment. It's also encouraged to adopt secure alternatives, such as SSH, which provide encrypted communication.

Impact​

Requires configuration adjustments to ensure legitimate traffic is not disrupted.

Audit​

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

  • The Direction is set to Inbound.

... see more

Remediation​

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Remediation​

From Command Line​

  1. Run the following command to remove or modify the unrestricted rule for Telnet access:
aws ec2 revoke-security-group-ingress \
--region {{region-name}} \
--group-id {{security-group-id}} \
--protocol {{protocol}} \
--port 23 \
--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==`23`].{CIDR:IpRanges[*].CidrIp,Port:FromPort}'
  1. Conduct tests to verify functionality of applications dependent on Telnet to ensure they are unaffected by the changes.
  2. Where possible, migrate services using Telnet to secure alternatives like SSH. Update configurations to use SSH and disable Telnet services.

policy.yaml​

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Linked Framework Sections​

SectionSub SectionsInternal RulesPoliciesFlagsCompliance
💼 AWS Foundational Security Best Practices v1.0.0 → 💼 [EC2.19] Security groups should not allow unrestricted access to ports with high risk10no data
💼 Cloudaware Framework → 💼 Threat Protection36no data
💼 FedRAMP High Security Controls → 💼 AC-4 Information Flow Enforcement (M)(H)23789no data
💼 FedRAMP High Security Controls → 💼 AC-4(21) Physical or Logical Separation of Information Flows (M)(H)1152no data
💼 FedRAMP High Security Controls → 💼 CM-2 Baseline Configuration (L)(M)(H)3130no data
💼 FedRAMP High Security Controls → 💼 CM-2(2) Automation Support for Accuracy and Currency (M)(H)16no data
💼 FedRAMP High Security Controls → 💼 CM-7 Least Functionality (L)(M)(H)31833no data
💼 FedRAMP High Security Controls → 💼 SC-7 Boundary Protection (L)(M)(H)10864no data
💼 FedRAMP High Security Controls → 💼 SC-7(4) External Telecommunications Services (M)(H)35no data
💼 FedRAMP High Security Controls → 💼 SC-7(5) Deny by Default — Allow by Exception (M)(H)18no data
💼 FedRAMP High Security Controls → 💼 SC-7(21) Isolation of System Components (H)28no data
💼 FedRAMP Low Security Controls → 💼 CM-2 Baseline Configuration (L)(M)(H)29no data
💼 FedRAMP Low Security Controls → 💼 CM-7 Least Functionality (L)(M)(H)29no data
💼 FedRAMP Low Security Controls → 💼 SC-7 Boundary Protection (L)(M)(H)40no data
💼 FedRAMP Moderate Security Controls → 💼 AC-4 Information Flow Enforcement (M)(H)173no data
💼 FedRAMP Moderate Security Controls → 💼 AC-4(21) Physical or Logical Separation of Information Flows (M)(H)52no data
💼 FedRAMP Moderate Security Controls → 💼 CM-2 Baseline Configuration (L)(M)(H)330no data
💼 FedRAMP Moderate Security Controls → 💼 CM-2(2) Automation Support for Accuracy and Currency (M)(H)16no data
💼 FedRAMP Moderate Security Controls → 💼 CM-7 Least Functionality (L)(M)(H)333no data
💼 FedRAMP Moderate Security Controls → 💼 SC-7 Boundary Protection (L)(M)(H)753no data
💼 FedRAMP Moderate Security Controls → 💼 SC-7(4) External Telecommunications Services (M)(H)35no data
💼 FedRAMP Moderate Security Controls → 💼 SC-7(5) Deny by Default — Allow by Exception (M)(H)18no data
💼 NIST CSF v2.0 → 💼 DE.CM-01: Networks and network services are monitored to find potentially adverse events150no data
💼 NIST CSF v2.0 → 💼 DE.CM-09: Computing hardware and software, runtime environments, and their data are monitored to find potentially adverse events149no data
💼 NIST CSF v2.0 → 💼 ID.AM-03: Representations of the organization's authorized network communication and internal and external network data flows are maintained76no data
💼 NIST CSF v2.0 → 💼 PR.DS-01: The confidentiality, integrity, and availability of data-at-rest are protected164no data
💼 NIST CSF v2.0 → 💼 PR.DS-02: The confidentiality, integrity, and availability of data-in-transit are protected140no data
💼 NIST CSF v2.0 → 💼 PR.DS-10: The confidentiality, integrity, and availability of data-in-use are protected156no data
💼 NIST CSF v2.0 → 💼 PR.IR-01: Networks and environments are protected from unauthorized logical access and usage103no data
💼 NIST SP 800-53 Revision 5 → 💼 AC-4 Information Flow Enforcement326999no data
💼 NIST SP 800-53 Revision 5 → 💼 AC-4(21) Information Flow Enforcement _ Physical or Logical Separation of Information Flows3752no data
💼 NIST SP 800-53 Revision 5 → 💼 CA-9(1) Internal System Connections _ Compliance Checks32no data
💼 NIST SP 800-53 Revision 5 → 💼 CM-2 Baseline Configuration729no data
💼 NIST SP 800-53 Revision 5 → 💼 CM-2(2) Baseline Configuration _ Automation Support for Accuracy and Currency16no data
💼 NIST SP 800-53 Revision 5 → 💼 CM-7 Least Functionality923no data
💼 NIST SP 800-53 Revision 5 → 💼 SC-7 Boundary Protection29466no data
💼 NIST SP 800-53 Revision 5 → 💼 SC-7(4) Boundary Protection _ External Telecommunications Services35no data
💼 NIST SP 800-53 Revision 5 → 💼 SC-7(5) Boundary Protection _ Deny by Default — Allow by Exception418no data
💼 NIST SP 800-53 Revision 5 → 💼 SC-7(11) Boundary Protection _ Restrict Incoming Communications Traffic28no data
💼 NIST SP 800-53 Revision 5 → 💼 SC-7(16) Boundary Protection _ Prevent Discovery of System Components29no data
💼 NIST SP 800-53 Revision 5 → 💼 SC-7(21) Boundary Protection _ Isolation of System Components28no data