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Mitigation Strategies Analysis for nuget/nuget.client

Mitigation Strategy: Explicitly Configure Trusted Package Sources

  • Description:

    1. Identify Trusted Sources: Determine which NuGet feeds are absolutely necessary and trustworthy. This likely includes a private internal feed and may include nuget.org or other public feeds, but only after careful vetting.
    2. Modify NuGet.Config: Edit the NuGet.Config file (typically located at %AppData%\NuGet\NuGet.Config for user-level, or in the solution/project directory).
    3. Clear Default Sources: Remove or disable the default nuget.org entry if it's not explicitly trusted for all packages.
    4. Add Trusted Sources: Add <add key="MyPrivateFeed" value="https://mycompany.pkgs.visualstudio.com/_packaging/MyFeed/nuget/v3/index.json" /> entries for each trusted source, providing the correct URL.
    5. Configure Credentials (if needed): If your private feed requires authentication, configure the necessary credentials within the NuGet.Config file or using environment variables, following secure credential management practices.
    6. Test Configuration: Run dotnet restore (or the equivalent in your build process) to ensure that packages are being restored from the expected sources. This uses NuGet.Client under the hood.
    7. Regular Review: Schedule periodic reviews (e.g., quarterly) of the NuGet.Config to ensure it remains up-to-date and reflects the current trust model.

  • List of Threats Mitigated:

    • Dependency Confusion/Substitution Attacks: (Severity: High) - Prevents attackers from publishing malicious packages with the same name as internal packages on a public feed, tricking the build system into downloading the malicious version.
    • Typosquatting Attacks: (Severity: Medium) - Reduces the risk of accidentally installing a package from a malicious source due to a typo in the package name or source URL.
    • Compromised Public Feed: (Severity: High) - Limits the impact if a public feed (like nuget.org) is compromised, as you're only using it for a limited, vetted set of packages (if at all).

  • Impact:

    • Dependency Confusion: Risk significantly reduced (almost eliminated if using Package Source Mapping in conjunction).
    • Typosquatting: Risk reduced, but not eliminated (human error is still possible).
    • Compromised Public Feed: Impact significantly reduced; only packages explicitly allowed from that source are affected.

  • Currently Implemented: Partially. NuGet.Config exists at the solution level and specifies our internal feed. nuget.org is also included, but not restricted.

  • Missing Implementation: nuget.org is not restricted via Package Source Mapping. We need to implement Package Source Mapping to fully mitigate dependency confusion. We also need a documented, regular review process for NuGet.Config.

Mitigation Strategy: Package Source Mapping

  • Description:

    1. Analyze Dependencies: Identify which packages come from which sources. Use dotnet list package --include-transitive to understand the full dependency graph.
    2. Edit NuGet.Config: Within the <packageSourceMapping> section of your NuGet.Config file, define mappings.
    3. Define Patterns: Use <packageSource> elements to specify patterns. For example: 
      <packageSourceMapping>
  <packageSource key="nuget.org">
    <package pattern="Newtonsoft.Json" />
    <package pattern="Microsoft.*" />
  </packageSource>
  <packageSource key="MyPrivateFeed">
    <package pattern="*" />
  </packageSource>
</packageSourceMapping>
      This example states that Newtonsoft.Json and packages starting with Microsoft. must come from nuget.org, while all other packages must come from MyPrivateFeed.
    4. Test Thoroughly: After implementing Package Source Mapping, thoroughly test the build and application to ensure that all dependencies are resolved correctly. Incorrect mappings can break the build. This testing directly exercises NuGet.Client's resolution logic.
    5. Regular Review: Review and update the mappings as dependencies change. This should be part of the dependency update process.

  • List of Threats Mitigated:

    • Dependency Confusion/Substitution Attacks: (Severity: High) - This is the primary mitigation for dependency confusion. It ensures that packages are only downloaded from their designated sources.
    • Compromised Public Feed: (Severity: High) - Further limits the impact of a compromised public feed by strictly controlling which packages can be sourced from it.

  • Impact:

    • Dependency Confusion: Risk almost eliminated when implemented correctly.
    • Compromised Public Feed: Impact significantly reduced; only explicitly mapped packages are at risk.

  • Currently Implemented: No.

  • Missing Implementation: This is entirely missing and needs to be implemented in the solution-level NuGet.Config.

Mitigation Strategy: Require Signed Packages

  • Description:

    1. Identify Trusted Signers: Determine which authors or repositories you trust to sign packages. This might involve using a company-internal CA or trusting specific public certificates.
    2. Configure NuGet.Config: Add a <trustedSigners> section to your NuGet.Config file.
    3. Add Signers: Add entries for each trusted signer, specifying their certificate details (e.g., fingerprint, subject name). You can trust authors or repositories.
    4. Set Verification Mode: Set the signatureValidationMode to require in the <config> section of NuGet.Config. This forces signature verification by NuGet.Client.
    5. Test: Attempt to install an unsigned package or a package signed by an untrusted signer. The installation should fail, confirming that NuGet.Client is enforcing the policy.
    6. Establish Signing Process: If you publish your own packages, establish a secure process for signing them using a trusted certificate.

  • List of Threats Mitigated:

    • Package Tampering: (Severity: High) - Prevents the installation of packages that have been modified after being signed.
    • Compromised Package Source (Partial Mitigation): (Severity: High) - Even if a package source is compromised, an attacker cannot inject a modified package without a valid signature. However, they could still serve an older, signed, vulnerable version (see rollback protection below).

  • Impact:

    • Package Tampering: Risk significantly reduced.
    • Compromised Package Source: Provides a strong layer of defense, but doesn't fully mitigate all risks.

  • Currently Implemented: No.

  • Missing Implementation: Needs to be implemented in the solution-level NuGet.Config. We also need to define our trusted signers.

Mitigation Strategy: Keep NuGet.Client Updated

  • Description:
    1. Check for Updates: Regularly check for updates to the NuGet client tools (e.g., dotnet, Visual Studio, NuGet Package Manager). These tools embed and use NuGet.Client.
    2. Update Tools: Install the latest stable versions of these tools.
    3. Automate (if possible): Consider automating the update process for build agents and developer machines.
  • List of Threats Mitigated:
    • Vulnerabilities in NuGet.Client: (Severity: Variable, from Low to Critical) - Reduces the risk of exploiting vulnerabilities in the NuGet client itself.
  • Impact:
    • Vulnerabilities in NuGet.Client: Reduces the risk, depending on the specific vulnerabilities patched in each update.
  • Currently Implemented: Partially. Developers are responsible for updating their own tools.
  • Missing Implementation: We need a more consistent process for ensuring build agents and developer machines are using up-to-date NuGet client tools. We could consider using a centralized package management system for developer tools.