NuGet's Security Gaps Exposed by npm Worm: What Protections Exist and What's Missing

In September 2025, a self-propagating worm called Shai-Hulud compromised over 500 npm packages by stealing maintainer credentials to publish malicious versions, prompting a CISA alert. The incident prompted scrutiny of whether a similar supply-chain attack could hit the NuGet ecosystem for .NET developers. NuGet does offer several defenses, including package signing with default verification since .NET 8, ID prefix reservation to block namespace impersonation, and OIDC-based Trusted Publishing to eliminate long-lived CI credentials. However, these controls only verify who published a package and that it was not tampered with in transit — they cannot determine whether the published code itself is malicious. Critically, a compromised or bad-faith maintainer account can still push harmful code that passes all current checks, and NuGet packages can carry executable logic that runs at build time, not just at runtime.