mitigations.md

Mitigation Strategies Analysis for mesonbuild/meson

Mitigation Strategy: Dependency Pinning and Verification (Meson wrap System)

Mitigation Strategy: Dependency Pinning and Verification (Meson wrap System)

• Description:

  1. Identify wrap Dependencies: List all external dependencies managed through Meson's wrap system (subprojects).
  2. wrap-file Mode: For dependencies fetched as archives, use the wrap-file mode in your [wrap-file] sections within the subprojects directory.
  3. Specify source_url: Provide the exact URL to the dependency's archive within the [wrap-file] section.
  4. Specify source_filename: Provide the exact filename of the dependency's archive within the [wrap-file] section.
  5. Calculate SHA-256 Hash: Download the dependency archive manually and calculate its SHA-256 checksum.
  6. Specify source_hash: Add the calculated SHA-256 hash to the source_hash field in the [wrap-file] section.
  7. wrap-git Mode: For dependencies fetched from Git repositories, use the wrap-git mode.
  8. Specify url: Provide the URL to the Git repository within the [wrap-git] section.
  9. Specify revision: Use the full 40-character commit hash (not a branch or tag) in the revision field of the [wrap-git] section.
  10. Regular Audits: Periodically review your subprojects/*.wrap files to ensure they are still pointing to the correct versions and hashes.

• Threats Mitigated:

  • Supply Chain Attacks (High Severity): Prevents attackers from injecting malicious code via compromised wrap dependencies.
  • Dependency Confusion (High Severity): Ensures you're using the intended version of a wrap dependency.
  • Accidental Dependency Updates (Medium Severity): Prevents unintended upgrades of wrap dependencies.

• Impact:

  • Supply Chain Attacks: Significantly reduces the risk for dependencies managed by wrap.
  • Dependency Confusion: Eliminates the risk for wrap dependencies.
  • Accidental Dependency Updates: Eliminates the risk for wrap dependencies.

• Currently Implemented:

  • (Example - Needs to be filled in): Partially implemented. wrap-file is used for some dependencies with SHA-256 hashes, but wrap-git dependencies are using branch names instead of commit hashes.

• Missing Implementation:

  • (Example - Needs to be filled in):
    • All wrap-git dependencies in subprojects/*.wrap files need to be updated to use full commit hashes.
    • A system for regularly auditing subprojects/*.wrap files needs to be established.

Mitigation Strategy: Code Review of meson.build Files

• Mitigation Strategy: Code Review of meson.build Files

• Description: (This strategy directly involves reviewing Meson build files, so it's included)

  1. Establish Review Process: Make review of all meson.build files (including those from dependencies brought in via wrap or direct dependencies) a mandatory part of your code review.
  2. Focus Areas (Meson-Specific):
     • run_command(): Scrutinize all uses of run_command().
     • Custom Targets: Examine custom targets that execute shell commands.
     • find_program(): Check how external programs are located and used, looking for potential PATH manipulation.
     • meson.get_compiler(): Review how compilers are obtained and configured.
     • dependency(): Examine how dependencies are declared and used.
     • File/Network Operations: Be wary of any unusual file or network access within the meson.build file.
  3. Multiple Reviewers: Have at least two developers review each meson.build file.
  4. Automated Checks (Optional): Develop or use linters/scripts to flag potentially dangerous constructs in meson.build files (e.g., searching for run_command()).

• Threats Mitigated:

  • Malicious meson.build Files (High Severity): Reduces the risk of malicious code in build files.
  • Unintentional Vulnerabilities in meson.build (Medium Severity): Helps identify and fix insecure coding practices within Meson build files.

• Impact:

  • Malicious meson.build Files: Significantly reduces the risk.
  • Unintentional Vulnerabilities: Reduces the risk by catching common mistakes.

• Currently Implemented:

  • (Example): Basic code review is performed, but it doesn't specifically focus on the security aspects of meson.build files. Dependency meson.build files are not consistently reviewed.

• Missing Implementation:

  • (Example):
    • Establish a formal process for reviewing all meson.build files, including those from dependencies.
    • Create checklists/guidelines for reviewing meson.build files for security.
    • Implement automated checks for potentially dangerous constructs.

Mitigation Strategy: Controlled Use of run_command() (within meson.build)

• Mitigation Strategy: Controlled Use of run_command() (within meson.build)

• Description:

  1. Minimize Usage: Avoid run_command() in your meson.build files whenever possible. Use Meson's built-in functions (e.g., dependency(), find_program(), custom targets, generators) instead.
  2. Input Validation: If you must use run_command(), rigorously validate and sanitize all inputs within your meson.build file, especially if they come from external sources or are derived from Meson variables that could be manipulated.
  3. Whitelisting: If possible, implement whitelisting within your meson.build file to restrict the commands that run_command() can execute.
  4. Avoid Shell Interpolation: Pass arguments to commands as separate strings in a list to run_command(), rather than constructing a single command string. Meson's API encourages this, but double-check.
  5. Error Handling: Check the return code and output of run_command() within your meson.build file to detect and handle errors.

• Threats Mitigated:

  • Command Injection (High Severity): Prevents attackers from injecting arbitrary commands via run_command() in meson.build.
  • Arbitrary Code Execution (High Severity): Reduces the risk of executing malicious code through run_command() in meson.build.

• Impact:

  • Command Injection: Significantly reduces the risk if input validation and whitelisting are correctly implemented within the meson.build file.
  • Arbitrary Code Execution: Reduces the risk by limiting the attack surface within the meson.build file.

• Currently Implemented:

  • (Example): run_command() is used in a few places in meson.build, but input validation is not consistently applied.

• Missing Implementation:

  • (Example):
    • Review all uses of run_command() in meson.build and implement rigorous input validation.
    • Replace run_command() calls with safer Meson alternatives where possible.
    • Implement whitelisting for allowed commands within meson.build, if feasible.

Mitigation Strategy: Explicit Compiler and Linker Flags (within meson.build)

• Mitigation Strategy: Explicit Compiler and Linker Flags (within meson.build)

• Description:

  1. Identify Security Flags: Research security-related compiler/linker flags for your platform and language.
  2. add_project_arguments: Use add_project_arguments in your meson.build file to add compiler flags for the entire project.
  3. add_global_arguments: Use add_global_arguments cautiously for global flags in your meson.build file.
  4. add_project_link_arguments: Use add_project_link_arguments in your meson.build file for linker flags.
  5. Language Specificity: Use the language keyword (e.g., language: 'c') in your meson.build file.
  6. Compiler Feature Checks: Use Meson functions like compiler.has_argument() in your meson.build file to check for compiler support before adding flags.
  7. Consistency: Ensure consistent flags across build configurations within your meson.build file.
  8. Documentation: Document flags and their purpose within your meson.build file or associated documentation.

• Threats Mitigated:

  • Buffer Overflows (High Severity): Flags like stack protection help.
  • Code Injection (High Severity): ASLR and DEP/NX make injection harder.
  • Return-oriented Programming (ROP) (High Severity): RELRO and similar flags increase ROP difficulty.

• Impact:

  • Buffer Overflows: Significantly reduces exploitability.
  • Code Injection: Makes injection significantly more difficult.
  • ROP: Increases the difficulty of ROP attacks.

• Currently Implemented:

  • (Example): Some basic compiler flags are set in meson.build, but not a comprehensive set of security flags. Linker flags are not explicitly configured for security.

• Missing Implementation:

  • (Example):
    • Add a comprehensive set of security-related compiler and linker flags to meson.build.
    • Implement compiler feature checks in meson.build for portability.
    • Document the purpose of each security flag in meson.build or related documentation.

Mitigation Strategy: Controlled Use of find_program() (within meson.build)

• Mitigation Strategy: Controlled Use of find_program() (within meson.build)

• Description:

  1. Minimize System PATH Reliance: When using find_program() in your meson.build file, be as specific as possible about the expected location of the program. Avoid relying solely on the system's PATH environment variable.
  2. required Keyword: Use the required: true keyword with find_program() in your meson.build file. This will cause the build to fail if the program is not found.
  3. version Keyword: If possible, use the version keyword to specify the required version of the program.
  4. native Keyword: Use native: true when the tool is needed by the build machine, and not for cross-compilation.
  5. check Method: Always check the .found() method of the object returned by find_program() in your meson.build file to ensure the program was actually found before using it.
  6. Alternatives: If dealing with a library, prefer using Meson's dependency() mechanism instead of find_program(). dependency() provides better control and version management.

• Threats Mitigated:

  • Dependency Hijacking (Medium Severity): Reduces the risk of an attacker placing a malicious executable in a location earlier in the PATH than the intended program.
  • Unexpected Program Behavior (Medium Severity): Ensures that the correct version of a program is used, preventing unexpected behavior due to version mismatches.

• Impact:

  • Dependency Hijacking: Reduces the risk by making it harder to hijack program lookups.
  • Unexpected Program Behavior: Improves build reliability and consistency.

• Currently Implemented:

  • (Example): find_program() is used in meson.build, but the required keyword and version checks are not consistently used. Reliance on PATH is not minimized.

• Missing Implementation:

  • (Example):
    • Review all uses of find_program() in meson.build and add the required: true keyword.
    • Specify version requirements using the version keyword where possible.
    • Minimize reliance on the system PATH by providing more specific paths.
    • Always check the .found() method before using the result of find_program().
    • Consider replacing find_program() with dependency() for libraries.

Mitigation Strategy: Reproducible Builds (Meson Configuration)

• Mitigation Strategy: Reproducible Builds (Meson Configuration)

• Description:

  1. Meson Options: Review Meson's documentation on reproducible builds and configure your meson.build and meson_options.txt files accordingly. This may involve:
     • Setting specific options related to timestamp handling.
     • Avoiding features that introduce non-determinism.
     • Using consistent compiler and linker flags (as covered in a previous strategy).
  2. Deterministic Inputs: Ensure all inputs to the build process are deterministic. This is primarily managed outside of Meson (e.g., using containers, pinning dependency versions), but your meson.build file should not introduce non-determinism.
  3. Avoid Non-Deterministic Constructs: Within your meson.build file, avoid:
     • Using the current date or time.
     • Generating random numbers.
     • Relying on external factors that might change between builds (e.g., network access).
  4. Verification: This is done outside of Meson, but is crucial for confirming reproducibility.

• Threats Mitigated:

  • Build Artifact Tampering (Medium Severity): Makes tampering easier to detect.
  • Supply Chain Attacks (Medium Severity): Helps verify the build process hasn't been compromised.

• Impact:

  • Build Artifact Tampering: Improves detection capabilities.
  • Supply Chain Attacks: Provides an additional layer of verification.

• Currently Implemented:

  • (Example): Not implemented. No specific steps have been taken in meson.build or meson_options.txt to ensure reproducible builds.

• Missing Implementation:

  • (Example):
    • Review Meson's documentation on reproducible builds and configure meson.build and meson_options.txt accordingly.
    • Ensure that meson.build does not introduce any non-deterministic behavior.