# CVE-2026-85184: @fastify/middie vulnerable to path-scoped middleware bypass via absolute-form request target

> Attackers can bypass path-scoped authentication middleware in Fastify applications by using absolute-form request targets, allowing unauthorized access to protected routes.

- **Severity:** Critical 9.1 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 4 Sep 2026
- **Updated:** 4 Sep 2026
- **Also known as:** GHSA-hx87-8wv7-pjv8

## What is CVE-2026-85184?

CVE-2026-85184 is a critical authentication bypass vulnerability in @fastify/middie, published on 4 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

@fastify/middie versions >= 9.1.0 and before 9.3.4 decide whether to run path-scoped middleware by matching against the raw request target, while the Fastify router resolves an absolute-form request target to its path before dispatching. Because the two layers evaluate different strings, a request using an absolute-form target reaches the route handler while the path-scoped middleware, such as authentication or authorization, is skipped. An unauthenticated network attacker can use this to bypass path-based access controls in a Fastify application that relies on middie for those controls. Users should upgrade to @fastify/middie 9.3.4 or later.

Weakness: CWE-436 (Interpretation Conflict)

## Which versions are affected by CVE-2026-85184?

It affects 1 product.


Products: Fastify Fastify\/Middie.

## How do I fix CVE-2026-85184?

No fix has been published for CVE-2026-85184 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-85184 being exploited?

There is no known exploitation of CVE-2026-85184 in the wild and no public exploit code.

## Other vulnerabilities in @fastify/middie

- [CVE-2026-14198](https://insights.sbomify.com/CVE-2026-14198/): @fastify/middie vulnerable to authorization bypass via encoded slash in path parameter values (critical 9.1)
- [CVE-2026-6270](https://insights.sbomify.com/CVE-2026-6270/): @fastify/middie vulnerable to middleware authentication bypass in child plugin scopes (critical 9.1)
- [CVE-2026-22031](https://insights.sbomify.com/CVE-2026-22031/): Fastify Middie Middleware Path Bypass (high 8.4)
- [CVE-2026-2880](https://insights.sbomify.com/CVE-2026-2880/): @fastify/middie has an improper path normalization vulnerability (high 8.2)
- [CVE-2026-14181](https://insights.sbomify.com/CVE-2026-14181/): @fastify/middie standalone engine vulnerable to Denial of Service via malformed percent-encoded paths (high 7.5)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-85184 and fix it if it is affected.

What it is: CVE-2026-85184 is a critical authentication bypass vulnerability in @fastify/middie, published on 4 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-85184 in the wild and no public exploit code.

Affected product: @fastify/middie. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-85184/ (Markdown: https://insights.sbomify.com/CVE-2026-85184/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-85184
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-85184
- OSV: https://osv.dev/vulnerability/CVE-2026-85184

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-85184/
Summaries are generated and may contain mistakes; the official description above is the record.