threat-modeling.md

Threat Model Analysis for letsencrypt/boulder

Threat: ACME Challenge Bypass

• Description: An attacker exploits a vulnerability in Boulder's ACME challenge verification logic (HTTP-01, DNS-01, TLS-ALPN-01) to bypass domain ownership validation. They craft requests that trick Boulder into issuing certificates for domains they do not control.
• Impact: Unauthorized certificate issuance for domains the attacker does not own. This enables man-in-the-middle attacks, phishing campaigns, and domain hijacking.
• Boulder Component Affected: ACME Server (Challenge Handlers, Validation Logic)
• Risk Severity: Critical
• Mitigation Strategies:
  • Thoroughly test and audit ACME challenge verification logic.
  • Implement robust input validation and sanitization.
  • Regularly update Boulder to the latest version with security patches.
  • Employ multiple validation methods where possible.
  • Implement monitoring and alerting for unusual certificate issuance patterns.

Threat: Vulnerabilities in Authorization Checks

• Description: A bug or logical flaw exists in Boulder's code responsible for authorization checks before certificate issuance. An attacker crafts a malicious request that exploits this vulnerability, bypassing intended authorization mechanisms and tricking Boulder into issuing certificates without proper validation.
• Impact: Potentially widespread unauthorized certificate issuance, leading to mass mis-issuance if the vulnerability is easily exploitable.
• Boulder Component Affected: ACME Server (Authorization Logic, Certificate Issuance Workflow)
• Risk Severity: Critical
• Mitigation Strategies:
  • Rigorous code reviews and security audits of authorization logic.
  • Implement comprehensive unit and integration tests covering authorization scenarios.
  • Employ static and dynamic code analysis tools to identify potential vulnerabilities.
  • Follow secure coding practices to minimize logical errors.

Threat: Code Injection Vulnerabilities

• Description: An attacker identifies and exploits code injection vulnerabilities (e.g., SQL injection, command injection) within Boulder's codebase. By crafting malicious input, they can inject and execute arbitrary code on the Boulder server.
• Impact: Full system compromise, data breaches (including private keys), denial of service, and manipulation of CA operations.
• Boulder Component Affected: Various Boulder Modules (depending on vulnerability location)
• Risk Severity: Critical
• Mitigation Strategies:
  • Employ secure coding practices to prevent code injection vulnerabilities.
  • Use parameterized queries or prepared statements to prevent SQL injection.
  • Sanitize and validate all user inputs.
  • Regularly perform static and dynamic code analysis.
  • Conduct penetration testing to identify injection vulnerabilities.

Threat: Operational Errors in Key Management

• Description: Human errors occur in the operational procedures for managing Boulder's private keys. This could include improper key generation, storage, rotation, or backup procedures.
• Impact: Key compromise due to mishandling, leading to full CA compromise and potential for widespread certificate mis-issuance.
• Boulder Component Affected: Key Management Procedures, Operational Processes
• Risk Severity: Critical
• Mitigation Strategies:
  • Implement robust and well-documented key management procedures.
  • Automate key management tasks where possible to reduce human error.
  • Use Hardware Security Modules (HSMs) for secure key generation and storage.
  • Train personnel on secure key management practices.
  • Regularly audit key management processes.

Threat: Account Compromise within Boulder

• Description: An attacker compromises an ACME account within Boulder. This could be through weak account security practices, vulnerabilities in Boulder's account management system, or insufficient access controls within the Boulder infrastructure.
• Impact: Unauthorized certificate issuance for domains associated with the compromised account. Potentially broader impact if account permissions are overly permissive.
• Boulder Component Affected: ACME Server (Account Management, Authorization Logic)
• Risk Severity: High
• Mitigation Strategies:
  • Enforce strong password policies for ACME accounts (if applicable).
  • Implement multi-factor authentication for administrative access to Boulder.
  • Regularly audit and review account permissions and access controls.
  • Securely store account credentials and API keys.
  • Monitor account activity for suspicious behavior.

Threat: Revocation Request Forgery or Manipulation

• Description: An attacker finds a vulnerability that allows them to forge or manipulate certificate revocation requests. They could either revoke valid certificates, causing denial of service, or prevent the revocation of compromised certificates.
• Impact: Denial of service by incorrectly revoking valid certificates. Continued use of compromised certificates if revocation is prevented. Erosion of trust in the CA.
• Boulder Component Affected: ACME Server (Revocation Request Handling), EAB Server (External Account Binding for Revocation)
• Risk Severity: High
• Mitigation Strategies:
  • Securely authenticate and authorize revocation requests.
  • Implement robust input validation and sanitization for revocation requests.
  • Use cryptographic signatures to protect the integrity of revocation requests.
  • Audit revocation requests and actions for suspicious activity.

Threat: Delayed or Failed Revocation Propagation

• Description: Issues in the process of propagating revocation information from Boulder's core system to OCSP responders and CRL distribution points. Delays or failures in propagation mean revocation status is not updated in a timely manner.
• Impact: A window of vulnerability where compromised certificates remain trusted by clients until revocation information is fully propagated.
• Boulder Component Affected: Revocation Propagation Mechanisms (from Core to OCSP/CRL)
• Risk Severity: High
• Mitigation Strategies:
  • Implement robust and reliable propagation mechanisms.
  • Monitor propagation processes for delays and failures.
  • Implement alerting for propagation issues.
  • Regularly test and verify revocation propagation.

Threat: Authentication and Authorization Bypass within Boulder

• Description: An attacker discovers vulnerabilities that allow them to bypass authentication or authorization mechanisms within Boulder's internal components or administrative interfaces. This grants them unauthorized access to sensitive functionalities.
• Impact: Unauthorized access to sensitive Boulder functionalities, potentially leading to configuration changes, data manipulation, certificate mis-issuance, or system compromise.
• Boulder Component Affected: Authentication and Authorization Modules, Administrative Interfaces
• Risk Severity: High
• Mitigation Strategies:
  • Implement robust authentication and authorization mechanisms.
  • Follow the principle of least privilege for access control.
  • Regularly audit and review access controls and permissions.
  • Securely configure administrative interfaces and restrict access.

Threat: Memory Safety Issues

• Description: Boulder code contains memory safety vulnerabilities like buffer overflows, use-after-free, or other memory corruption issues. An attacker can exploit these vulnerabilities, potentially leading to crashes, denial of service, or remote code execution.
• Impact: Denial of service, system instability, or in severe cases, remote code execution and full system compromise.
• Boulder Component Affected: Various Boulder Modules (depending on vulnerability location, often in C/C++ components if used)
• Risk Severity: High
• Mitigation Strategies:
  • Use memory-safe programming languages where possible.
  • Employ memory safety tools and techniques during development (e.g., static analysis, fuzzing).
  • Regularly update dependencies and libraries to patch known memory safety vulnerabilities.
  • Implement runtime memory safety checks if feasible.

Threat: Logic Errors in Certificate Processing

• Description: Logical flaws exist in Boulder's certificate processing logic. An attacker crafts specific certificate requests that exploit these flaws, leading to unexpected behavior, security vulnerabilities, or incorrect certificate issuance.
• Impact: Issuance of malformed or insecure certificates, vulnerabilities exploitable through crafted certificate requests, potential for denial of service or other unexpected behavior.
• Boulder Component Affected: Certificate Processing Modules (e.g., Certificate Generation, Validation)
• Risk Severity: High
• Mitigation Strategies:
  • Rigorous testing of certificate processing logic with various valid and invalid inputs.
  • Formal verification techniques where applicable.
  • Code reviews focusing on logical correctness and edge cases.
  • Fuzzing certificate processing components with malformed or unusual certificate requests.

Threat: Protocol Confusion or Exploitation

• Description: An attacker exploits ambiguities or weaknesses in Boulder's implementation of the ACME protocol. This could involve sending unexpected or malformed ACME messages that trigger unintended behavior or security vulnerabilities in Boulder's protocol handling.
• Impact: Unintended actions, security breaches, or denial of service due to protocol implementation flaws.
• Boulder Component Affected: ACME Server (Protocol Handling, Message Parsing)
• Risk Severity: High
• Mitigation Strategies:
  • Adhere strictly to the ACME protocol specifications.
  • Implement robust protocol parsing and validation.
  • Conduct thorough testing of ACME protocol implementation with various valid and invalid messages.
  • Participate in ACME protocol standardization and interoperability testing.

Threat: Insecure Session Management in ACME

• Description: Weaknesses in how Boulder manages ACME sessions, potentially allowing session hijacking or unauthorized access to ACME accounts. This could involve predictable session identifiers, insecure session storage, or lack of proper session expiration.
• Impact: Account takeover and unauthorized certificate management by hijacking ACME sessions.
• Boulder Component Affected: ACME Server (Session Management)
• Risk Severity: High
• Mitigation Strategies:
  • Use strong, unpredictable session identifiers.
  • Securely store session data (e.g., encrypted storage).
  • Implement proper session expiration and timeout mechanisms.
  • Use HTTPS for all ACME communication to protect session data in transit.

Threat: Insecure Configuration of Boulder

• Description: Boulder is misconfigured with insecure settings. This could include weak key generation parameters, insecure storage of private keys, overly permissive access controls, or insecure network configurations.
• Impact: Weakened security posture, increased risk of key compromise, unauthorized access, and other vulnerabilities.
• Boulder Component Affected: Configuration Files, Deployment Settings
• Risk Severity: High
• Mitigation Strategies:
  • Follow security best practices for Boulder configuration.
  • Use strong key generation parameters and secure key storage mechanisms (HSM if applicable).
  • Implement least privilege access controls.
  • Secure network configurations (firewalls, network segmentation).
  • Regularly review and audit Boulder configurations.