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.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- None listed
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.
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.
Upgrade, and check permissions on every request on the server, not only in the interface. More about Missing authorization.
Is CVE-2026-90982 being exploited?
There is no known exploitation of CVE-2026-90982 in the wild and no public exploit code.
Sources
Also known as GHSA-r799-r9gc-m956.