GHSA-8p85-9qpw-fwgw — @fastify/middie
Fix: fastify/middie@140e0ddGHSA-8p85-9qpw-fwgw is a Improper Input Validation vulnerability in @fastify/middie. A fix is available for @fastify/middie — see the affected versions and patch details below.
@fastify/middie has Improper Path Normalization when Using Path-Scoped Middleware
Exploitation Status
No confirmed exploitation observed yet
- CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.
Exploitation and automatability from CISA’s SSVC triage for GHSA-8p85-9qpw-fwgw.
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.
Real-World Exposure
How broadly this vulnerability is actually deployed: weekly install volume shows current usage, and reverse-dependency count shows how many other packages break if it stays unpatched.
@fastify/middienpmDescription
Summary
A path normalization inconsistency in @fastify/middie can result in authentication/authorization bypass when using path-scoped middleware (for example, app.use('/secret', auth)).
When Fastify router normalization options are enabled (such as ignoreDuplicateSlashes, useSemicolonDelimiter, and related trailing-slash behavior), crafted request paths may bypass middleware checks while still being routed to protected handlers.
Impact
An unauthenticated remote attacker can access endpoints intended to be protected by middleware-based auth/authorization controls by sending specially crafted URL paths (for example, //secret or /secret;foo=bar), depending on router option configuration.
This may lead to unauthorized access to protected functionality and data exposure.
Affected versions
- Confirmed affected:
@fastify/[email protected] - All versions prior to the patch are affected.
Patched versions
- Fixed in: 9.2.0
Details
The issue is caused by canonicalization drift between:
@fastify/middiepath matching forapp.use('/prefix', ...), and- Fastify/find-my-way route lookup normalization.
Because middleware and router did not always evaluate the same normalized path, auth middleware could be skipped while route resolution still succeeded.
Workarounds
Until patched version is deployed:
- Avoid relying solely on path-scoped middie guards for auth/authorization.
- Enforce auth at route-level handlers/hooks after router normalization.
- Disable risky normalization combinations only if operationally feasible.
Resources
- Fluid Attacks Disclosure Policy: https://fluidattacks.com/advisories/policy
- Fluid Attacks advisory URL: https://fluidattacks.com/advisories/jimenez
Credits
- Cristian Vargas (Fluid Attacks Research Team) — discovery and report.
- Oscar Uribe (Fluid Attacks) — coordination and disclosure.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 📦npm | @fastify/middie | all versions | 9.2.0npm install @fastify/middie@9.2.0 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for @fastify/middie, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update @fastify/middie to 9.2.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-8p85-9qpw-fwgw 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 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like GHSA-8p85-9qpw-fwgw can be triaged on real exposure rather than presence alone.
Tailored to GHSA-8p85-9qpw-fwgw. 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-8p85-9qpw-fwgw in your dependencies?
O3 Security finds GHSA-8p85-9qpw-fwgw across npm dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.