threat-modeling.md

Threat Model Analysis for smallstep/certificates

Threat: Weak Key Generation

• Threat: Weak Key Generation
• Description: An attacker could exploit cryptographically weak private keys generated by step or the application. They might use brute-force or other cryptanalytic techniques to compromise the key. Once compromised, the attacker can impersonate the application, decrypt communications, or sign malicious code as if it were legitimate.
• Impact: Critical. Full compromise of application identity and security, leading to data breaches, service disruption, and reputational damage.
• Affected Component: step CLI, Application Key Generation Logic, Cryptographic Libraries
• Risk Severity: Critical
• Mitigation Strategies:
  • Configure step-ca to enforce strong key generation parameters (e.g., key size, algorithm).
  • Use cryptographically secure random number generators (CSPRNGs) in application code.
  • Regularly audit key generation processes and configurations.
  • Consider using Hardware Security Modules (HSMs) for key generation to ensure hardware-backed entropy.

Threat: Insecure Key Storage during Generation

• Threat: Insecure Key Storage during Generation
• Description: During the certificate generation process, private keys might be temporarily written to disk in temporary files, stored in memory without proper protection, or transmitted insecurely. An attacker gaining access to the system during this brief window could steal the private key.
• Impact: High. Compromise of private key leading to impersonation, decryption of communications, and potential data breaches.
• Affected Component: step CLI, Application Key Generation Logic, Operating System Temporary File System, System Memory
• Risk Severity: High
• Mitigation Strategies:
  • Minimize temporary storage of private keys.
  • Use secure memory handling practices to prevent keys from being swapped to disk.
  • Ensure proper cleanup of temporary files immediately after key generation.
  • Encrypt temporary storage locations if temporary storage is unavoidable.

Threat: Unauthorized Certificate Issuance

• Threat: Unauthorized Certificate Issuance
• Description: An attacker could gain unauthorized access to the step-ca server or its API. This could be through compromised credentials, exploiting vulnerabilities in the step-ca server, or social engineering. Once access is gained, the attacker can issue certificates for domains or services they do not control, effectively impersonating legitimate entities.
• Impact: Critical. Allows attackers to impersonate any service, conduct man-in-the-middle attacks, and bypass authentication, leading to complete system compromise.
• Affected Component: step-ca Server, step-ca API, Authentication and Authorization Mechanisms
• Risk Severity: Critical
• Mitigation Strategies:
  • Implement strong authentication and authorization for access to step-ca and its API (e.g., mutual TLS, API keys with strict permissions).
  • Regularly audit access logs and configurations of step-ca.
  • Harden the step-ca server and keep it updated with security patches.
  • Implement network segmentation to restrict access to step-ca to only authorized systems.

Threat: Misconfiguration of Certificate Profiles and Policies

• Threat: Misconfiguration of Certificate Profiles and Policies
• Description: Administrators might misconfigure certificate profiles or policies within step-ca, leading to the issuance of certificates with overly broad permissions (e.g., wildcard certificates where not needed), excessively long validity periods, or weak security parameters (e.g., allowing weak key algorithms). This expands the attack surface and increases the potential impact of compromised certificates.
• Impact: High. Increased attack surface, longer window of opportunity for misuse of compromised certificates, and potential for misuse of overly permissive certificates.
• Affected Component: step-ca Configuration, Certificate Profiles, Certificate Policies
• Risk Severity: High
• Mitigation Strategies:
  • Carefully define and regularly review certificate profiles and policies.
  • Implement the principle of least privilege when defining certificate permissions.
  • Use short certificate validity periods where appropriate.
  • Enforce strong security parameters in certificate profiles (e.g., minimum key size, allowed algorithms).
  • Use configuration management tools to ensure consistent and auditable configurations.

Threat: Domain Validation Bypass

• Threat: Domain Validation Bypass
• Description: If the application relies on domain validation mechanisms provided by step-ca (e.g., ACME HTTP-01, DNS-01), vulnerabilities in these mechanisms or misconfigurations could allow an attacker to bypass validation and obtain certificates for domains they do not legitimately control. This allows them to impersonate those domains.
• Impact: High. Attackers can impersonate legitimate domains and services, leading to phishing attacks, man-in-the-middle attacks, and reputational damage.
• Affected Component: step-ca ACME Server, Domain Validation Mechanisms (HTTP-01, DNS-01), DNS Infrastructure
• Risk Severity: High
• Mitigation Strategies:
  • Ensure robust domain validation methods are used and properly configured in step-ca.
  • Regularly review and test domain validation processes.
  • Monitor DNS records for unauthorized changes if using DNS-01 validation.
  • Use HTTPS for ACME HTTP-01 challenges to prevent interception.

Threat: Insecure Storage of Private Keys (Application Side)

• Threat: Insecure Storage of Private Keys (Application Side)
• Description: Private keys used by the application for TLS, mutual TLS, or signing operations might be stored insecurely on the application server. This could include storing them in plaintext files, weakly encrypted storage, or in locations accessible to unauthorized users or processes. An attacker gaining access to the application server could steal these keys.
• Impact: Critical. Compromise of private keys leading to impersonation, decryption of communications, and potential data breaches.
• Affected Component: Application Server, Key Storage Mechanisms (File System, Databases, etc.), Application Code
• Risk Severity: Critical
• Mitigation Strategies:
  • Store private keys securely using Hardware Security Modules (HSMs) or secure key management systems (KMS).
  • If HSM/KMS is not feasible, use encrypted storage with strong encryption algorithms and access controls.
  • Implement strict access control lists (ACLs) and role-based access control (RBAC) for the certificate and key store.

Threat: Unauthorized Access to Certificate and Key Store (Application Side)

• Threat: Unauthorized Access to Certificate and Key Store (Application Side)
• Description: Insufficient access controls on the application's certificate and key store could allow unauthorized users, processes, or even vulnerabilities in the application itself to access and potentially steal private keys and certificates. This could be due to weak file permissions, insecure application design, or vulnerabilities in the application code.
• Impact: High. Compromise of private keys and certificates, leading to impersonation and data breaches.
• Affected Component: Application Server, Key Storage Mechanisms, Operating System Access Control, Application Code
• Risk Severity: High
• Mitigation Strategies:
  • Implement strict access control lists (ACLs) and role-based access control (RBAC) for the certificate and key store.
  • Regularly audit access logs to the certificate and key store.
  • Apply the principle of least privilege to application processes accessing keys.
  • Harden the application server and keep it updated with security patches.

Threat: Accidental Exposure of Private Keys

• Threat: Accidental Exposure of Private Keys
• Description: Private keys could be unintentionally exposed through various channels due to developer errors, misconfigurations, or inadequate security practices. This includes logging private key material, including keys in unencrypted backups, hardcoding keys in configuration files or code, or committing keys to version control systems.
• Impact: Critical. Compromise of private keys, leading to impersonation, decryption of communications, and potential data breaches.
• Affected Component: Logging Systems, Backup Systems, Configuration Management, Version Control Systems, Application Code
• Risk Severity: Critical
• Mitigation Strategies:
  • Implement secure logging practices and avoid logging sensitive data like private keys.
  • Encrypt backups containing private keys.
  • Avoid hardcoding private keys in configuration files or code.
  • Use secrets management solutions to manage and inject secrets securely.
  • Implement pre-commit hooks and automated scanning tools to prevent accidental commits of secrets to version control.
  • Regularly scan logs, backups, and code repositories for exposed secrets.

Threat: Key Leakage through Side Channels

• Threat: Key Leakage through Side Channels
• Description: Side-channel attacks, such as timing attacks or power analysis, could potentially leak private key information from the application server's memory or hardware. These attacks exploit subtle variations in execution time, power consumption, or electromagnetic radiation to infer key material.
• Impact: High. Potential compromise of private keys, depending on the attacker's capabilities and the effectiveness of side-channel mitigations.
• Affected Component: Application Server Hardware, Cryptographic Libraries, Operating System
• Risk Severity: High
• Mitigation Strategies:
  • Employ cryptographic libraries and hardware resistant to side-channel attacks.
  • Implement mitigations at the application and system level to reduce side-channel leakage (e.g., constant-time algorithms, address space layout randomization).
  • Regularly update cryptographic libraries and operating systems with security patches that address side-channel vulnerabilities.

Threat: Failure to Revoke Compromised Certificates

• Threat: Failure to Revoke Compromised Certificates
• Description: If a certificate is compromised (e.g., private key stolen), the revocation process might fail due to operational issues, misconfiguration in step-ca, or lack of monitoring of revocation status. This leaves the compromised certificate valid and usable by attackers even after the compromise is detected.
• Impact: High. Compromised certificates remain valid and can be misused for an extended period, allowing continued impersonation and attacks.
• Affected Component: step-ca Revocation Functionality, Certificate Revocation Lists (CRLs), Online Certificate Status Protocol (OCSP)
• Risk Severity: High
• Mitigation Strategies:
  • Implement a robust certificate revocation process using step-ca's revocation features.
  • Regularly test and monitor the revocation process to ensure it is functioning correctly.
  • Automate the revocation process as much as possible to reduce manual errors and delays.
  • Implement alerts and monitoring for certificate compromise events to trigger revocation promptly.

Threat: Ineffective Revocation Mechanisms (CRL/OCSP)

• Threat: Ineffective Revocation Mechanisms (CRL/OCSP)
• Description: If the revocation mechanisms used (CRL, OCSP) are not properly implemented, maintained, or are inaccessible to clients, clients might not be able to effectively check certificate revocation status. This could be due to misconfiguration of step-ca, network connectivity issues, or DoS attacks on revocation services. Clients might then accept revoked certificates as valid.
• Impact: High. Clients might accept revoked certificates as valid, leading to security breaches and allowing attackers to use compromised certificates undetected.
• Affected Component: step-ca CRL/OCSP Services, CRL Distribution Points, OCSP Responders, Client Certificate Validation Logic
• Risk Severity: High
• Mitigation Strategies:
  • Ensure proper configuration and availability of CRL and/or OCSP services provided by step-ca.
  • Regularly monitor the health and accessibility of revocation services.
  • Implement redundancy and caching for revocation services to improve availability and performance.
  • Configure clients to properly check certificate revocation status and handle revocation failures gracefully (e.g., fail-closed approach).

Threat: Denial of Service of Revocation Services

• Threat: Denial of Service of Revocation Services
• Description: Revocation services (CRL, OCSP) could be targeted by denial-of-service (DoS) attacks. If these services become unavailable, clients might be unable to verify certificate revocation status. In some cases, clients might be configured to bypass revocation checks if the services are unavailable, leading to acceptance of potentially revoked certificates.
• Impact: High. Clients might be forced to bypass revocation checks or accept potentially revoked certificates, increasing the risk of accepting compromised certificates. Service disruption for applications relying on revocation checks.
• Affected Component: step-ca CRL/OCSP Services, CRL Distribution Points, OCSP Responders, Network Infrastructure
• Risk Severity: High
• Mitigation Strategies:
  • Implement DoS protection for revocation services (e.g., rate limiting, firewalls, content delivery networks).
  • Consider redundancy and caching mechanisms to improve resilience of revocation services.
  • Configure clients to handle revocation service unavailability securely (e.g., fail-closed approach, fallback mechanisms).

Threat: Improper Certificate Validation (Application Side)

• Threat: Improper Certificate Validation (Application Side)
• Description: The application might not properly validate server certificates presented during TLS/mTLS connections. This could involve failing to verify the certificate chain of trust, not checking certificate expiration dates, skipping hostname verification, or ignoring revocation status. Accepting invalid certificates can expose the application to man-in-the-middle attacks and malicious servers.
• Impact: Critical. Man-in-the-middle attacks, exposure to malicious servers, and data breaches due to accepting fraudulent certificates.
• Affected Component: Application TLS/mTLS Implementation, Certificate Validation Logic, Cryptographic Libraries
• Risk Severity: Critical
• Mitigation Strategies:
  • Implement strict certificate validation in the application using robust TLS libraries.
  • Verify the certificate chain of trust up to a trusted root CA.
  • Check certificate expiration dates and validity periods.
  • Perform hostname verification to ensure the certificate is valid for the expected server hostname.
  • Implement revocation checking (CRL/OCSP) to verify the certificate is not revoked.
  • Regularly update TLS libraries to ensure they incorporate the latest security best practices.

Threat: Certificate Pinning Issues

• Threat: Certificate Pinning Issues
• Description: Incorrect implementation or management of certificate pinning can lead to two main issues: * Bypass: If pinning is not correctly enforced or can be circumvented, attackers can still perform MitM attacks. * Bricking: Incorrect pinning configuration or lack of proper certificate rotation mechanisms can lead to application failures if legitimate certificates are updated or rotated.
• Impact: High. MitM attacks if pinning is bypassed. Application unavailability or service disruption if pinning is misconfigured and causes "bricking".
• Affected Component: Application TLS/mTLS Implementation, Certificate Pinning Logic, Certificate Management Processes
• Risk Severity: High
• Mitigation Strategies:
  • Carefully implement certificate pinning, if used, and thoroughly test the implementation.
  • Ensure proper key rotation and certificate update mechanisms are in place to avoid application failures due to pinning.
  • Consider using dynamic pinning or backup pins to improve flexibility and resilience.
  • Monitor certificate expiration and rotation schedules to proactively update pins.
  • If possible, avoid hardcoding pins directly in the application and use configuration mechanisms for easier updates.

Threat: Improper Certificate Chain Building and Validation

• Threat: Improper Certificate Chain Building and Validation
• Description: The application might not correctly build and validate the entire certificate chain presented by a server. This could lead to accepting certificates signed by untrusted or compromised intermediate CAs, even if the root CA is trusted. Incorrect chain validation can bypass the intended trust model and allow MitM attacks.
• Impact: High. Acceptance of malicious certificates and potential MitM attacks due to flawed chain validation.
• Affected Component: Application TLS/mTLS Implementation, Certificate Chain Validation Logic, Cryptographic Libraries
• Risk Severity: High
• Mitigation Strategies:
  • Use robust TLS libraries that correctly handle certificate chain building and validation.
  • Ensure the application trusts only the intended root CA(s) and properly validates the chain up to the root.
  • Regularly update TLS libraries to incorporate security patches and best practices for chain validation.
  • Test certificate chain validation logic thoroughly with various valid and invalid certificate chains.

Threat: Weak Passphrases for Key Encryption

• Threat: Weak Passphrases for Key Encryption
• Description: If private keys are encrypted at rest using passphrases (e.g., when stored on disk), using weak passphrases makes them vulnerable to brute-force attacks. An attacker gaining access to the encrypted key file could easily decrypt it if the passphrase is weak.
• Impact: High. Compromise of private keys if encryption is bypassed due to weak passphrases, leading to impersonation and data breaches.
• Affected Component: Key Storage Mechanisms, Key Encryption Processes, Password Management
• Risk Severity: High
• Mitigation Strategies:
  • Enforce strong passphrase policies for key encryption (minimum length, complexity requirements).
  • Use key derivation functions (KDFs) like Argon2, bcrypt, or scrypt to strengthen passphrases and make brute-force attacks more computationally expensive.
  • Consider using password managers or secrets management tools to generate and manage strong passphrases.
  • Prefer hardware-backed key storage (HSMs) or KMS where passphrases are not directly involved in key protection.

Threat: Loss of Private Keys

• Threat: Loss of Private Keys
• Description: Private keys could be lost due to various reasons, including hardware failures, accidental deletion, inadequate backup procedures, or natural disasters. Loss of keys can lead to service disruptions, inability to decrypt data, and the need for certificate re-issuance and system reconfiguration.
• Impact: High. Service disruptions, data inaccessibility, operational overhead for key recovery and re-issuance.
• Affected Component: Key Storage Mechanisms, Backup Systems, Disaster Recovery Processes
• Risk Severity: High
• Mitigation Strategies:
  • Implement robust key backup and recovery procedures.
  • Store backups securely and separately from the primary key storage location.
  • Test key recovery processes regularly to ensure they are functional.
  • Consider using redundant key storage mechanisms (e.g., HSM clusters, distributed KMS).
  • Implement versioning and audit trails for key management operations.

Threat: Key Compromise due to Insider Threats

• Threat: Key Compromise due to Insider Threats
• Description: Malicious insiders with privileged access to systems, key stores, or step-ca infrastructure could intentionally compromise private keys for malicious purposes. This could involve stealing keys, modifying key material, or issuing unauthorized certificates.
• Impact: Critical. Significant security breaches, impersonation, data theft, and potential long-term damage due to intentional malicious actions by trusted insiders.
• Affected Component: Key Management Processes, Access Control Systems, Personnel Security, step-ca Infrastructure, Application Infrastructure
• Risk Severity: Critical
• Mitigation Strategies:
  • Implement strong access controls and the principle of least privilege for all systems and key stores.
  • Enforce separation of duties to prevent any single individual from having complete control over key management processes.
  • Implement comprehensive monitoring and auditing of privileged access and key management operations.
  • Conduct thorough background checks and security awareness training for personnel with access to sensitive key material.
  • Implement incident response plans to detect and respond to insider threats effectively.