Fastify fastify-static up to 10.1.3 Route Guard improper authorization

Summaryinfo

A vulnerability classified as problematic has been found in Fastify fastify-static up to 10.1.3. The affected element is an unknown function of the component Route Guard. Performing a manipulation results in improper authorization. This vulnerability is known as CVE-2026-90982. Remote exploitation of the attack is possible. No exploit is available. It is recommended to upgrade the affected component.

Detailsinfo

A vulnerability, which was classified as problematic, was found in Fastify fastify-static up to 10.1.3. This affects some unknown processing of the component Route Guard. The manipulation with an unknown input leads to a improper authorization vulnerability. CWE is classifying the issue as CWE-285. The product does not perform or incorrectly performs an authorization check when an actor attempts to access a resource or perform an action. This is going to have an impact on confidentiality. The summary by CVE is:

@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.

It is possible to read the advisory at github.com. This vulnerability is uniquely identified as CVE-2026-90982 since 09/14/2026. The exploitability is told to be easy. It is possible to initiate the attack remotely. No form of authentication is needed for exploitation. The technical details are unknown and an exploit is not publicly available. The attack technique deployed by this issue is T1548.002 according to MITRE ATT&CK.

Upgrading to version 10.1.4 eliminates this vulnerability.

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Productinfo

Vendor

• Fastify

Name

• fastify-static

Version

• 10.1.0
• 10.1.1
• 10.1.2
• 10.1.3

Website

• Product: https://github.com/fastify/fastify-static/

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