ASP.NET Core: Checking NuGet Dependencies for Known Vulnerabilities

Introduction

A .NET application can contain vulnerable dependencies even when its own code has no obvious security flaw. These dependencies may be direct packages referenced by the project or transitive packages pulled in by another library.

Regular dependency audits help teams identify known vulnerabilities, assess exposure, and prioritize remediation before a release reaches production.

1. Understand direct and transitive dependencies

A direct dependency is explicitly referenced by your project. A transitive dependency is brought in by another package.

For example, an ASP.NET Core application might reference an HTTP client library that depends on additional packages. Those transitive packages can also introduce vulnerabilities.

Inspect the dependency tree and package versions rather than reviewing only the entries in the project file. The package that introduces a vulnerable dependency may not be the package that needs to be updated.

2. Use the .NET CLI to find vulnerable packages

Run the vulnerability audit command from the relevant project or solution directory:

dotnet list package --vulnerable --include-transitive

This reports known vulnerabilities identified by the package tooling and available vulnerability information. Command syntax and output can vary across SDK versions.

You can also inspect outdated dependencies:

dotnet list package --outdated

A package being outdated does not automatically mean it is vulnerable, and a package that is current is not automatically free from security issues. Treat these as separate checks.

3. Assess severity and actual exposure

A vulnerability report is a starting point for investigation. Review the advisory, affected versions, fixed versions, severity, and conditions required for exploitation.

Ask practical questions:

• Is the vulnerable code used by the application?
• Is the affected functionality reachable from an untrusted request?
• Does the vulnerability apply to this package version and runtime?
• Is a patched version available?
• Would upgrading introduce breaking changes that need additional testing?

Do not ignore a vulnerability merely because the affected code appears unused. Dependency reachability can be difficult to establish, and a package may be invoked indirectly.

4. Upgrade the responsible package

Update the direct package that introduces the vulnerable dependency when an appropriate fix is available:

dotnet add package Example.Library --version 2.4.1

The package name and version are illustrative; choose a verified fixed version from the relevant security advisory.

If the vulnerable dependency is transitive, you may need to upgrade the parent package that brings it in. Adding a direct reference to force a transitive version can sometimes work, but it must be compatible with the parent library and should not replace a proper upstream fix without review.

After updating, restore packages and rerun the vulnerability audit.

5. Integrate auditing into CI

Manual checks are useful, but they can be forgotten during busy release cycles. Run dependency audits in continuous integration and decide which findings should block a build.

For example, a pipeline step can execute:

dotnet restore
dotnet list package --vulnerable --include-transitive
dotnet build --no-restore
dotnet test

For strict enforcement, configure the pipeline to fail when policy-defined vulnerability conditions are met. Do not assume that every informational command automatically returns a failure status for every finding; verify the behavior of the SDK and use the appropriate audit configuration for your pipeline.

Also consider dependency review tools, repository security alerts, and automated update proposals.

6. Verify the fix before release

After upgrading a package, run tests that cover the affected behavior. Check API compatibility, serialization, authentication, database access, and other relevant integration points.

Then confirm that the vulnerability no longer appears in the dependency audit and review the final dependency tree. Keep a record of accepted risks and the reasoning behind any temporary exceptions.

A patched dependency is important, but an untested upgrade can introduce availability or correctness problems of its own.

7. Make dependency security an ongoing process

A one-time audit cannot protect an application indefinitely because new vulnerabilities are discovered over time.

Include dependency checks in routine maintenance, release preparation, and incident response. Keep package updates manageable, monitor security advisories for critical dependencies, and make it easy for the team to understand who owns remediation.

Conclusion

NuGet vulnerability auditing helps .NET teams discover known risks in both direct and transitive dependencies. Combine automated scanning with advisory review, tested upgrades, and clear remediation policies to make dependency security a repeatable part of the release process.