Nest: Middleware Bypass on Fastify via Trailing Slash

### Impact An authentication bypass vulnerability exists in `@nestjs/platform-fastify` (confirmed on version `11.1.24`, the latest available release at time of report). When middleware is registered through NestJS's `MiddlewareConsumer.forRoutes()` API on the Fastify adapter, an unauthenticated client can bypass the Nest middleware registered for that route by simply appending a trailing slash (`/`) to the request URL. This bypass works on the **default Fastify adapter configuration** — no special router options need to be enabled. Applications using the standard CRUD route shape (`GET /resource` and `GET /resource/:id`) are affected when they protect those routes with `MiddlewareConsumer.forRoutes()` middleware. ### Patches Fixed in `@nestjs/[email protected]` ### References Kudos goes to @a-tt-om

Source published

15 Jun 2026 20:36:43 UTC

Source modified

18 Jul 2026 17:30:30 UTC

Observed here

24 Oct 2026 13:17:17 UTC

Source terms

GitHub Advisory Database · CC-BY-4.0

Original source record · Cite this exact observation · Complete original publisher JSON

This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: osv · GitHub Advisory Database · CC-BY-4.0. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS_V4 · CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:H/VI:H/VA:L/SC:N/SI:N/SA:N

Publisher rating · HIGH