Adding a crates.io Security tab

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+- Feature Name: crates-io-security
+- Start Date: 2025-10-27
+- RFC PR: [rust-lang/rfcs#3872](https://github.com/rust-lang/rfcs/pull/3872)
+- Rust Issue: [rust-lang/rust#3872](https://github.com/rust-lang/rust/issues/3872)
+
+# Summary
+[summary]: #summary
+
+This RFC proposes that crates.io should provide insight into vulnerabilities and unsound
+API surface based on the RustSec advisory database.
+
+# Motivation
+[motivation]: #motivation
+
+One of the roles that crates.io serves for Rust developers is as a discovery mechanism for library
+packages. As such, it is important that users can quickly assess the quality of a given crate,
+including security considerations such as unsound code/API or known vulnerabilities.
+The RustSec advisory database is a curated database of security advisories for Rust crates,
+which tracks known vulnerabilities, unsound code, and maintenance status of crates.
+
+The Rust ecosystem has a culture of having smaller, focused crates with a clear purpose.
+As a result, many Rust projects have a large number of dependencies, which increases the
+risk of introducing problems in the final artifact via the supply chain of dependencies.
+
+We've seen an increasing number of security issues via transitive dependencies:
+
+* In 2024, some releases of the popular xz-utils package (written in C) contained
+  a [malicious backdoor] affecting OpenSSH servers running on the local system.
+* In 2025, a phishing campaign [targeted crates.io users] using the `rustfoundation.dev` domain
+  name to impersonate the Rust Foundation and steal maintainer's credentials.
+
+While known actively malicious crates would be deleted from crates.io by the responsible team,
+unintentional vulnerabilities and unsound APIs can still pose a risk to Rust developers.
+
+The Open Source Security Foundation (OpenSSF) has enumerated [Principles for Package Repository
+Security]; while crates.io already addresses many of these, one of these is:
+
+> The package repository warns of known security vulnerabilities in dependencies in the package
+> repository UI.
+
+The RustSec advisory database tooling already supports exporting advisories in the OSV format.
+
+[malicious backdoor]: https://en.wikipedia.org/wiki/XZ_Utils_backdoor
+[targeted crates.io users]: https://blog.rust-lang.org/2025/09/12/crates-io-phishing-campaign/
+[Principles for Package Repository Security]: https://repos.openssf.org/principles-for-package-repository-security.html
+
+# Guide-level explanation
+[guide-level-explanation]: #guide-level-explanation
+
+The crates.io website will display information about known vulnerabilities and unsound APIs.
+This might take the form of a Security tab on a crate's page. If there are known vulnerabilities
+for the currently selected version, the tab might be highlighted. The Security tab will be
+there whether there are existing advisories for a crate or not, and the linked page will show
+a message indicating that there are no published advisories if that is the case.
+
+Opening the Security tab for a crate should show a list of advisories that affect the crate,
+including a summary of the issue, a list of affected versions, and links to more information.
+Care should be taken to ensure that the mere existence of past vulnerabilities does not negatively
+impact the perceived quality of a crate; very popular crates are much more likely to have
+vulnerabilities reported against them, simply due to their popularity and the amount of scrutiny.
+
+The Security tab should give Rust developers a quick overview of the security status of a crate,
+and allow them to make informed decisions about whether to use the crate in their projects.
+
+While this information is available today via the RustSec website (including feeds that can
+automatically be consumed by tooling), having this information directly on crates.io would
+make it accessible and visible to a wider audience.
+
+# Reference-level explanation
+[reference-level-explanation]: #reference-level-explanation
+
+The RustSec project publishes a number of Rust crates that can be used to parse and query the
+advisory database, which can be reused in the crates.io codebase. For now, crates.io will only
+display advisories in the UI; we will not be adding API to query RustSec advisories. Downstream
+users who want to consume this data can use the RustSec crates and the [advisory-db repository]
+directly.
+
+[advisory-db repository]: https://github.com/RustSec/advisory-db
+
+# Drawbacks
+[drawbacks]: #drawbacks
+
+The RustSec project is maintained by an independent team of volunteers, so the crates.io Security
+tab will be reflecting data that is maintained by what amounts to a kind of third party.
+The Leadership Council has an [ongoing discussion] on governance for the Secure Code WG that
+governs the RustSec project, which might be relevant to this proposal.
+
+Rust developers might be scared off of using crates that have known vulnerabilities, even if
+those vulnerabilities are not relevant to their use case, or have been fixed in later versions.
+This seems like a reasonable trade-off to me -- we should allow informed users to make decisions
+that are best for their projects.
+
+[ongoing discussion]: https://github.com/rust-lang/leadership-council/issues/140
+
+# Rationale and alternatives
+[rationale-and-alternatives]: #rationale-and-alternatives
+
+crates.io is the official package repository for the Rust ecosystem, so sharing important security
+context via this interface seems like an effective way to make it accessible to a wide audience.
+
+Widely used tools like [cargo-audit] and [cargo-deny] already provide a way to check for
+security-sensitive issues in a Rust project's dependencies, but these tools are opt-in and require
+users to be aware of them and to run them. They are also more focused on auditing a project's
+existing dependencies rather than helping inform users in the discovery phase.
+
+Alternatively, we might make the RustSec advisory database available directly via cargo. This
+seems mostly unrelated to what crates.io does, and seems like an interesting future possibility.
+
+[cargo-audit]: https://crates.io/crates/cargo-audit
+[cargo-deny]: https://crates.io/crates/cargo-deny
+
+# Prior art
+[prior-art]: #prior-art
+
+Neither npm nor PyPI currently seem to provide support for displaying security advisories.
+
+# Unresolved questions
+[unresolved-questions]: #unresolved-questions
+
+This seems like a relatively straightforward feature with a limited scope. The main questions
+are about the desirability of the feature, the implementation approach, and the governance
+of the source data.
+
+# Future possibilities
+[future-possibilities]: #future-possibilities
+
+In the future, it would be valuable if lockfile updates exposed open vulnerabilities in a
+project's dependency graph in the Cargo CLI, for example on `cargo update` or `cargo check`.
+
+crates.io could extend its existing API to query advisories for a given crate.