A redirect vulnerability in the `fastify-static` module version >= 4.2.4 and < 4.4.1 allows remote attackers to redirect Mozilla Firefox users to arbitrary websites via a double slash `//` followed by a domain: `http://localhost:3000//a//youtube.com/%2e%2e%2f%2e%2e`.A DOS vulnerability is possible if the URL contains invalid characters `curl --path-as-is "http://localhost:3000//^/.."`The issue shows up on all the `fastify-static` applications that set `redirect: true` option. By default, it is `false`.

Affected: npm: fastify-static

### Impact

A redirect vulnerability in the `fastify-static` module allows remote attackers to redirect Mozilla Firefox users to arbitrary websites via a double slash `//` followed by a domain: `http://localhost:3000//a//youtube.com/%2e%2e%2f%2e%2e`.

A DOS vulnerability is possible if the URL contains invalid characters `curl --path-as-is "http://localhost:3000//^/.."`

The issue shows up on all the `fastify-static` applications that set `redirect: true` option. By default, it is `false`.

### Patches The issue has been patched in `fastify-static@4.4.1`

### Workarounds If updating is not an option, you can sanitize the input URLs using the [`rewriteUrl`](https://www.fastify.io/docs/latest/Server/#rewriteurl) server option.

### References

+ Bug founder: drstrnegth + [hackerone Report](https://hackerone.com/reports/1361804)

### For more information If you have any questions or comments about this advisory: * Open an issue in [fastify-static](https://github.com/fastify/fastify-static) * Contact the [security team](https://github.com/fastify/fastify/blob/main/SECURITY.md#the-fastify-security-team)