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attack-surface.md

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Attack Surface Analysis for letsencrypt/boulder

Attack Surface: ACME Request Parsing Vulnerabilities

  • Description: Flaws in how Boulder parses and processes incoming ACME requests. Malformed or malicious requests could exploit these vulnerabilities.
  • Boulder Contribution: Boulder's ACME protocol handling logic is the entry point for all certificate issuance requests. Bugs in this code directly expose the system to parsing vulnerabilities.
  • Example: An attacker crafts a specially crafted ACME request with an overly long field that triggers a buffer overflow in Boulder's request parsing code, leading to denial of service or potentially remote code execution.
  • Impact: Denial of Service, Remote Code Execution, Information Disclosure.
  • Risk Severity: High to Critical (depending on the vulnerability).
  • Mitigation Strategies:
    • Input Validation: Developers should implement robust input validation and sanitization for all ACME request fields within Boulder's code.
    • Fuzzing and Security Audits: Boulder developers should regularly perform fuzzing and security audits of the ACME request parsing code to identify and fix vulnerabilities.
    • Use Safe Parsing Libraries: Boulder developers should utilize well-vetted and secure parsing libraries to minimize the risk of parsing errors.
    • Rate Limiting: Boulder's configuration should include rate limiting on ACME request processing to mitigate DoS attacks exploiting parsing vulnerabilities.

Attack Surface: Domain Validation Bypass (DNS Challenge Manipulation)

  • Description: Attackers circumventing domain ownership validation, specifically DNS-01 challenges, to obtain certificates for domains they do not control.
  • Boulder Contribution: Boulder relies on DNS-01 challenges as a primary validation method. Weaknesses in the validation process or reliance on potentially manipulable DNS infrastructure contribute to this attack surface. Boulder's validation logic is directly responsible for the security of this process.
  • Example: An attacker exploits a vulnerability in a DNS provider's infrastructure or performs a DNS cache poisoning attack to temporarily control DNS records for a target domain. They then use this temporary control to pass Boulder's DNS-01 challenge and obtain a certificate for the domain.
  • Impact: Unauthorized Certificate Issuance, Domain Impersonation, Phishing Attacks.
  • Risk Severity: High.
  • Mitigation Strategies:
    • Multi-Perspective Validation: Boulder developers should implement validation from multiple network perspectives within Boulder's validation logic to reduce the risk of localized DNS manipulation.
    • DNSSEC Validation: Boulder should, if possible, validate DNS records using DNSSEC to ensure their authenticity and integrity.
    • Challenge Re-verification: Boulder's design should include periodic re-verification of DNS challenges during the certificate lifecycle to detect and revoke certificates issued based on temporary DNS control.
    • Consider Alternative Validation Methods: Boulder's configuration and documentation should offer and encourage the use of HTTP-01 or TLS-ALPN-01 challenges where appropriate, as they may be less susceptible to DNS-related attacks in certain scenarios.

Attack Surface: Private Key Exposure (Insecure Key Storage)

  • Description: Compromise of the CA's private keys due to insecure storage practices.
  • Boulder Contribution: Boulder is responsible for generating and storing the critical CA private keys. Insecure storage practices within the Boulder deployment environment directly lead to this attack surface. Boulder's key management design and instructions for deployment are crucial here.
  • Example: The server hosting Boulder is compromised due to a separate vulnerability. An attacker gains access to the filesystem and finds the CA private keys stored in plaintext or with weak encryption, allowing them to impersonate the CA.
  • Impact: Complete CA Compromise, Trust Anchor Breach, Widespread Certificate Forgery.
  • Risk Severity: Critical.
  • Mitigation Strategies:
    • Hardware Security Modules (HSMs): Boulder's deployment documentation and best practices should strongly recommend storing CA private keys in HSMs, which provide tamper-proof and secure key storage.
    • Strong Encryption at Rest: If HSMs are not used, Boulder's documentation should mandate encrypting private keys at rest using strong encryption algorithms and robust key management practices.
    • Access Control: Users deploying Boulder must implement strict access controls to limit access to the server and storage locations where private keys are stored, as guided by Boulder's security documentation.
    • Regular Security Audits: Users deploying Boulder should conduct regular security audits of the key storage and management infrastructure to identify and remediate vulnerabilities, following security guidelines provided by Boulder.
    • Principle of Least Privilege: Users deploying Boulder should grant only necessary permissions to users and processes accessing the key storage system, adhering to the principle of least privilege as part of secure Boulder deployment.

Attack Surface: SQL Injection Vulnerabilities

  • Description: Exploiting vulnerabilities in SQL queries used by Boulder to access its database, allowing attackers to execute arbitrary SQL commands.
  • Boulder Contribution: Boulder relies on a database to store critical data like account information, authorizations, and certificate metadata. SQL injection vulnerabilities in Boulder's database interactions directly expose this data. Boulder's code interacting with the database is the direct source of this risk.
  • Example: An attacker crafts a malicious ACME request that injects SQL code into a database query used by Boulder to process account registration. This allows the attacker to bypass authentication, extract sensitive data, or modify database records.
  • Impact: Data Breach, Data Manipulation, Account Takeover, Denial of Service.
  • Risk Severity: High to Critical (depending on the vulnerability and data exposed).
  • Mitigation Strategies:
    • Parameterized Queries/Prepared Statements: Boulder developers must use parameterized queries or prepared statements for all database interactions within Boulder's codebase to prevent SQL injection.
    • Input Sanitization: Boulder developers should sanitize and validate all user inputs before incorporating them into database queries, even when using parameterized queries as a defense in depth measure within Boulder's code.
    • Principle of Least Privilege (Database): Users deploying Boulder should grant the Boulder application only the minimum necessary database privileges required for its operation, as part of secure deployment practices.
    • Regular Security Audits (Code and Database): Boulder developers should conduct regular security audits of Boulder's codebase and database interactions to identify and remediate SQL injection vulnerabilities. Users should also audit their database configurations.

Attack Surface: Vulnerabilities in External Dependencies

  • Description: Security flaws present in third-party libraries and frameworks that Boulder depends on.
  • Boulder Contribution: Boulder, like most software, relies on external libraries. Vulnerabilities in these dependencies are indirectly part of Boulder's attack surface. Boulder's choice of dependencies and how it integrates them is the contributing factor.
  • Example: A critical vulnerability is discovered in a widely used Go library that Boulder utilizes for TLS handling. Attackers exploit this vulnerability in Boulder to perform a man-in-the-middle attack or gain remote code execution.
  • Impact: Wide range of impacts depending on the vulnerability, including Remote Code Execution, Denial of Service, Information Disclosure, etc.
  • Risk Severity: Medium to Critical (depending on the vulnerability and dependency).
  • Mitigation Strategies:
    • Dependency Scanning and Management: Boulder developers should implement automated dependency scanning tools to identify known vulnerabilities in Boulder's dependencies and integrate this into their development process.
    • Regular Dependency Updates: Boulder developers must keep all dependencies up-to-date with the latest security patches and provide clear guidance to users on how to update dependencies in their deployments.
    • Vulnerability Monitoring: Boulder developers should subscribe to security advisories and vulnerability databases for the libraries Boulder uses and proactively address reported issues.
    • Vendor Security Practices Review: Boulder developers should consider the security practices and track record of library vendors when selecting dependencies.
    • Dependency Pinning/Vendoring: Boulder's build process should utilize dependency pinning or vendoring to ensure consistent and controlled dependency versions and reduce the risk of unexpected updates introducing vulnerabilities. Boulder should also guide users on managing dependencies in their deployments.