Auditing package dependencies for security vulnerabilities

About security audits

A security audit for package managers like NuGet is a process that involves analyzing the security of the packages that are included in a software project. This involves identifying vulnerabilities, evaluating risks, and making recommendations for improving security. The audit can include a review of the packages themselves, as well as any dependencies and their associated risks. The goal of the audit is to identify and mitigate any security vulnerabilities that could be exploited by attackers, such as code injection or cross-site scripting attacks.

We also have a blog post which discusses our recommended method for taking action when a package with a known vulnerability is found to be used by your project, and tools to help get more information.

Feature availability

NuGet	.NET SDK	Visual Studio	Feature
5.9	.NET 5 SDK (5.0.200)	N/A	dotnet list package --vulnerable
6.8	.NET 8 SDK (8.0.100)	Visual Studio 2022 17.8	NuGetAudit for PackageReference
6.10	N/A	Visual Studio 2022 17.10	NuGetAudit for packages.config
6.11	.NET 8 SDK (8.0.400)	Visual Studio 2022 17.11	NuGetAuditSuppress for PackageReference
6.12	.NET 9 SDK (9.0.100)	Visual Studio 2022 17.12	Audit sources. NuGetAuditSuppress for packages.config.

Running a security audit with restore

The restore command automatically runs when you do a common package operation such as loading a project for the first time, adding a new package, updating a package version, or removing a package from your project in your favorite IDE. Your dependencies are checked against a list of known vulnerabilities provided by your audit sources.

1. On the command line, navigate to your project or solution directory.
2. Run restore using your preferred tooling (i.e. dotnet, MSBuild, NuGet.exe, VisualStudio etc).
3. Review the warnings and address the known security vulnerabilities.

Configuring NuGet Audit

Audit can be configured via MSBuild properties in a .csproj or MSBuild file being evaluated as part of your project. We recommend that audit is configured at a repository level.

MSBuild Property	Default	Possible values	Notes
NuGetAuditMode	all (1)	direct and all	If you'd like to audit both top-level and transitive dependencies, you can set the value to all. NuGetAuditMode is not applicable for packages.config projects
NuGetAuditLevel	low	low, moderate, high, and critical	The minimum severity level to report. If you'd like to see moderate, high, and critical advisories (exclude low), set the value to moderate
NuGetAudit	true	true and false	If you wish to not receive security audit reports, you can opt-out of the experience entirely by setting the value to false

(1) NuGetAuditMode defaulted to direct when it was introduced in the .NET 8.0.100 SDK and VS 17.8. In .NET 9.0.100 SDK and VS 17.12 the default changed to all.

Audit Sources

Restore downloads a server's VulnerabilityInfo resource to check against the list of packages each project is using. The list of sources are defined by the auditSources element in NuGet.Config, and warning NU1905 is raised if any of the audit sources do not provide any vulnerability info. If auditSources is not defined or is cleared without adding any sources, then packageSources will be used and warning NU1905 is suppressed.

Since a common mitigation for package substitution attacks is to use a single package source that upstreams from nuget.org, so that NuGet is not configured to use nuget.org as a package source, audit sources can be used to use nuget.org (or any other source that provides vulnerability information) without also using it as a package source.

The data source for nuget.org's vulnerability database is GitHub Advisory Database. Note that the V2 protocol is deprecated, so if your nuget.config is still using the V2 endpoint, you must migrate to the V3 endpoint.

<configuration>
    <auditSources>
        <clear />
        <add key="nuget.org" value="https://api.nuget.org/v3/index.json" />
    </auditSources>
</configuration>

Audit sources are available from NuGet 6.12, .NET 9.0.100 SDK, and Visual Studio 2022 17.12. Prior to this version, NuGet Audit will only use package sources to download vulnerability information. Audit sources are not used by dotnet list package --vulnerable at this time.

Excluding advisories

You can choose to exclude specific advisories from the audit report by adding a new NuGetAuditSuppress MSBuild item for each advisory. Define a NuGetAuditSuppress item with the Include= metadata set to the advisory URL you wish to suppress.

<ItemGroup>
    <NuGetAuditSuppress Include="https://github.com/advisories/XXXX" />
</ItemGroup>

Similar to the other NuGet audit configuration properties, NuGetAuditSuppress items can be defined at the project or repository level.

NuGetAuditSuppress is available for PackageReference projects starting from NuGet 6.11, Visual Studio 17.11, and the .NET 8.0.400 SDK. It is available for packages.config with Visual Studio 17.12 and NuGet 6.12.

Warning codes

Warning Code	Reason
NU1900	Error communicating with package source, while getting vulnerability information.
NU1901	Package with low severity detected
NU1902	Package with moderate severity detected
NU1903	Package with high severity detected
NU1904	Package with critical severity detected
NU1905	An audit source does not provide a vulnerability database

You can customize your build to treat these warnings as errors to treat warnings as errors, or treat warnings not as errors. For example, if you're already using <TreatWarningsAsErrors> to treat all (C#, NuGet, MSBuild, etc) warnings as errors, you can use <WarningsNotAsErrors>NU1901;NU1902;NU1903;NU1904</WarningsNotAsErrors> to prevent vulnerabilities discovered in the future from breaking your build. Alternatively, if you want to keep low and moderate vulnerabilities as warnings, but treat high and critical vulnerabilities as errors, and you're not using TreatWarningsAsErrors, you can use <WarningsAsErrors>NU1903;NU1904</WarningsAsErrors>.

Note

MSBuild properties for message severity such as NoWarn and TreatWarningsAsErrors are not supported for packages.config projects.

dotnet list package --vulnerable

Once a project is successfully restored, dotnet list package has a --vulnerable argument to filter the packages based on which packages have known vulnerabilities. Note that --include-transitive is not default, so should be included

Actions when packages with known vulnerabilities are reported

We also have a blog post which discusses our recommended method for taking action when a package with a known vulnerability is found to be used by your project, and tools to help get more information.

Security vulnerabilities found with updates

If security vulnerabilities are found and updates are available for the package, you can either:

• Edit the .csproj or other package version location (Directory.Packages.props) with a newer version containing a security fix.
• Use the NuGet package manager user interface in Visual Studio to update the individual package.
• Run the dotnet add package command with the respective package ID to update to the latest version.

Security vulnerabilities found with no updates

In the case that a known vulnerability exists in a package without a security fix, you can do the following.

• Check for any mitigating factors outlined in the advisory report.
• Use a suggested package if the package is marked deprecated or is abandoned.
• If the package is open source, consider contributing a fix.
• Open an issue in the package's issue tracker.

Check for mitigating factors

Review the security advisor for any mitigating factors that may allow you to continue using the package with the vulnerability. The vulnerability may only exist when the code is used on a specific framework, operating system, or a special function is called.

Use a suggested package

In the case that a security advisory is reported for the package you're using and the package is marked deprecated or seems abandoned, consider using any suggested alternate package the package author has declared or a package comprising of similar functionality that is maintained.

Contribute a fix

If a fix does not exist for the security advisory, you may want to suggest changes that addresses the vulnerability in a pull request on package's open source repository or contact the author through the Contact owners section on the NuGet.org package detail page.

Open an issue

If you do not want to fix the vulnerability or are unable to update or replace the package, open an issue in the package's issue tracker or preferred contact method. On NuGet.org, you can navigate to the package details page and click Report package which will guide you to get in contact with the author.

No security vulnerabilities found

If no security vulnerabilities are found, this means that packages with known vulnerabilities were not found in your package graph at the present moment of time you checked. Since the advisory database can be updated at any time, we recommend regularly checking your dotnet restore output and ensuring the same in your continuous integration process.

Summary

Security auditing features are crucial for maintaining the security and integrity of software projects. These features provide you with an additional layer of protection against security vulnerabilities and ensures that you can use open source packages with confidence.