# CVE-2026-90982: @fastify/static vulnerable to route guard bypass via path case-folding

> Attackers can bypass route guards to read protected files on case-insensitive filesystems by altering path letter case.

- **Severity:** Medium 5.3 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/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:** 17 Sep 2026
- **Updated:** 17 Sep 2026
- **Also known as:** GHSA-r799-r9gc-m956

## What is CVE-2026-90982?

CVE-2026-90982 is a medium-severity missing authorization vulnerability in @fastify/static, published on 17 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

@fastify/static is a Fastify plugin that serves static files from a configured root directory. In versions before 10.1.4, on a case-insensitive filesystem such as Windows or the default macOS volume, a route guard or allowedPath restriction can be bypassed by altering the letter case of a path segment. The route matcher is case-sensitive while the filesystem is not, so a request that changes the case of a protected segment does not match the guarded route and falls through to the static handler, yet the filesystem resolves it to the same protected file. As a result, an unauthenticated request can read a file that a route guard or allowedPath was configured to protect. The issue does not affect case-sensitive filesystems and is not a directory traversal, since nothing is served from outside the configured root. The issue is fixed in @fastify/static 10.1.4, which validates the requested path against its actual on-disk spelling and rejects case-aliased paths before authorization. As a workaround, serve static files from a case-sensitive filesystem, or ensure route guards and allowedPath rules account for every letter-case variant of the protected paths.

Weakness: CWE-284 (Improper Access Control), CWE-178 (Improper Handling of Case Sensitivity)

## Which versions are affected by CVE-2026-90982?


## How do I fix CVE-2026-90982?

No fix has been published for CVE-2026-90982 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-90982 being exploited?

There is no known exploitation of CVE-2026-90982 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-90982 and fix it if it is affected.

What it is: CVE-2026-90982 is a medium-severity missing authorization vulnerability in @fastify/static, published on 17 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-2026-90982 in the wild and no public exploit code.

Affected product: @fastify/static. 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-2026-90982/ (Markdown: https://insights.sbomify.com/CVE-2026-90982/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-90982
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-90982
- OSV: https://osv.dev/vulnerability/CVE-2026-90982

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-90982/
Summaries are generated and may contain mistakes; the official description above is the record.