GHSA-r4wm-x892-vjmx
Nest has a Fastify URL Encoding Middleware Bypass
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
Blast Radius
Weekly download volume for affected packages — a proxy for how broadly this vulnerability is deployed.
@nestjs/platform-fastifynpmDescription
Impact
What kind of vulnerability is it? Who is impacted?
A NestJS application using @nestjs/platform-fastify can allow bypass of any middleware when Fastify path-normalization options (e.g., ignoreTrailingSlash, ignoreDuplicateSlashes, useSemicolonDelimiter) are enabled. In affected route-scoped middleware setups, variant paths may skip middleware checks while still reaching the protected handler.
The bug is a path canonicalization mismatch between middleware matching and route matching in Nest’s Fastify adapter.
Nest passes Fastify routerOptions (such as ignoreTrailingSlash, ignoreDuplicateSlashes, useSemicolonDelimiter) to the Fastify router in packages/platform-fastify/adapters/fastify-adapter.ts:253.
But middleware execution is decided by a separate regex check over req.originalUrl in packages/platform-fastify/adapters/fastify-adapter.ts:706 and packages/platform-fastify/adapters/fastify-adapter.ts:713.
If that regex does not match, Nest does next() and skips the middleware (packages/platform-fastify/adapters/fastify-adapter.ts:714), while Fastify may still normalize the same path and route it to the protected handler. So the vulnerability exists because security checks (middleware) and request dispatch(router) use different URL interpretations.
This is a fail-open design issue (inconsistent normalization), not just a bad app config: non-default router options make the mismatch reachable.
Patches
Fixed in @nestjs/[email protected]
References
Credit goes to Fluidattacks (Cristian Vargas) https://fluidattacks.com/advisories/neton
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 📦npm | @nestjs/platform-fastify | all versions | 11.1.14 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for @nestjs/platform-fastify. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.
Fix
Update @nestjs/platform-fastify to 11.1.14 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-r4wm-x892-vjmx is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 pinpoints whether GHSA-r4wm-x892-vjmx is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.
Tailored to GHSA-r4wm-x892-vjmx. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is GHSA-r4wm-x892-vjmx in your dependencies?
O3 detects GHSA-r4wm-x892-vjmx across npm dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.