threat-modeling.md

Threat Model Analysis for homebrew/homebrew-cask

Threat: Compromised Cask Repository

• Threat: Compromised Cask Repository
• Description: An attacker gains control of a Homebrew Cask repository (official or a third-party tap). They inject malicious cask definitions or modify existing ones. This allows them to distribute malware by manipulating the cask formula to download malicious binaries or execute malicious scripts during the brew cask install process.
• Impact: Users installing casks from the compromised repository unknowingly install malware, backdoors, or compromised applications. This can lead to complete system compromise, data theft, and loss of control over the affected system.
• Affected Component: Cask Repositories (GitHub repositories, Git infrastructure), Cask Definition Retrieval mechanism.
• Risk Severity: Critical
• Mitigation Strategies:
  • Prioritize Official Repository: Primarily rely on the official homebrew/cask repository as it has a higher level of scrutiny.
  • Thorough Tap Vetting: If using third-party taps, rigorously vet them for security practices, reputation, and maintainer trustworthiness before adding them. Regularly audit and review used taps.
  • Repository Integrity Monitoring: Monitor official and used tap repositories for unusual commits, unauthorized changes, or suspicious activity.
  • HTTPS Enforcement: Ensure all communication with cask repositories is strictly over HTTPS to prevent man-in-the-middle attacks during repository updates and cask definition retrieval.
  • Checksum Verification (Feature Request): Advocate for and ideally implement checksum verification of cask definitions and downloaded application binaries within Homebrew Cask itself to ensure integrity.

Threat: Malicious Cask Install Scripts

• Threat: Malicious Cask Install Scripts
• Description: Attackers inject malicious code into the install, uninstall, or other lifecycle scripts embedded within a cask definition. When a user executes brew cask install for a compromised cask, this malicious code is executed on their system with the user's privileges. This can enable attackers to perform actions like downloading and executing further malware, modifying system settings for persistence, or exfiltrating sensitive data.
• Impact: Arbitrary code execution on the user's system with user privileges. This can result in significant system compromise, including data theft, malware installation, creation of backdoors, and potentially privilege escalation if combined with other vulnerabilities.
• Affected Component: Cask Definitions (Ruby scripts within cask files), brew cask install command execution, Ruby interpreter used by Homebrew Cask.
• Risk Severity: High
• Mitigation Strategies:
  • Manual Cask Definition Review: Before installing any cask, especially from less familiar sources, manually review the cask definition file. Pay close attention to the install and other script blocks, looking for suspicious, obfuscated, or unexpected code.
  • Static Analysis Tooling (Future Enhancement): Develop or utilize static analysis tools specifically designed to scan cask definitions for potentially malicious code patterns or behaviors.
  • Least Privilege Installation Practices: Run brew cask install under a user account with the lowest necessary privileges to limit the potential damage from malicious script execution. Avoid running brew cask install as root or administrator.
  • Sandboxing/Containerization (Advanced Mitigation): Explore and implement sandboxing or containerization technologies to isolate the brew cask install process, restricting its access to the broader system and limiting the impact of malicious scripts.
  • Community Vetting and Reporting: Rely on community vigilance and reporting mechanisms to identify and flag suspicious or malicious casks. Encourage users to share their cask reviews and security findings.