GHSA-x428-ghpx-8j92 CVE-2026-6414
@fastify/static vulnerable to route guard bypass via encoded path separators
- Severity
- 5.9 / 10
- Medium · CVSS 3.1
- Exploit chance (EPSS)
- 0.42%
- Chance of exploitation in the next 30 days. Higher than 36.53% of scored vulnerabilities.
- Known exploited
- No
- Not in CISA's catalog
- Weakness
- CWE-177 Improper Handling of URL Encoding (Hex Encoding)
- Fix
9.1.1- Upgrade @fastify/static to this version or later
Description
Impact
@fastify/static v9.1.0 and earlier decodes percent-encoded path separators (%2F) before filesystem resolution, but Fastify's router treats them as literal characters. This creates a routing mismatch: route guards on /admin/* do not match /admin%2Fsecret.html, but @fastify/static decodes it to /admin/secret.html and serves the file.
Applications that rely on route-based middleware or guards to protect files served by @fastify/static can be bypassed with encoded path separators.
Patches
Upgrade to @fastify/static >= 9.1.1.
Workarounds
None. Upgrade to the patched version.
Affected versions
npm
| Package | Vulnerable | Fixed in |
|---|---|---|
| @fastify/static | >= 8.0.0, < 9.1.1 |
9.1.1 |
How to fix
Move to the fixed version or later with your package manager, update the lockfile, and run your tests. If the package only arrives through another dependency, upgrade that dependency first. If none of its releases pulls a fixed version yet, force the version with your package manager's override.
@fastify/static npm → 9.1.1
- npm
npm install @fastify/static@9.1.1- yarn
yarn add @fastify/static@9.1.1- pnpm
pnpm add @fastify/static@9.1.1
Severity breakdown
CVSS 3.1 5.9
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N
- Attack vector
- Network
- Attack complexity
- High
- Privileges required
- None
- User interaction
- None
- Scope
- Unchanged
- Confidentiality
- High
- Integrity
- None
- Availability
- None
Weakness
CWE-177: Improper Handling of URL Encoding (Hex Encoding)
The product does not properly handle when all or part of an input has been URL encoded.
How to prevent it
- Architecture and Design: Avoid making decisions based on names of resources (e.g. files) if those resources can have alternate names.
- Implementation: Assume all input is malicious. Use an "accept known good" input validation strategy, i.e., use a list of acceptable inputs that strictly conform to specifications. Reject any input that does not strictly conform to specifications, or transform it into something that does. When performing input validation, consider all potentially relevant properties, including length, type of input, the full range of acceptable values, missing or extra inputs, syntax, consistency across related fields, and conformance to business rules. As an example of business rule logic, "boat" may be syntactically valid because it only contains alphanumeric characters, but it is not valid if the input is only expected to contain colors such as "red" or "blue." Do not rely exclusively on looking for malicious or malformed inputs. This is likely to miss at least one undesirable input, especially if the code's environment changes. This can give attackers enough room to bypass the intended validation. However, denylists can be useful for detecting potential attacks or determining which inputs are so malformed that they should be rejected outright.
- Implementation: Inputs should be decoded and canonicalized to the application's current internal representation before being validated (CWE-180). Make sure that the application does not decode the same input twice (CWE-174). Such errors could be used to bypass allowlist validation schemes by introducing dangerous inputs after they have been checked.
References
Advisories
Packages
Other links
Timeline
- Published
- Last updated by the source
- Latest EPSS score
Related advisories
| Advisory | Severity | Why it's related |
|---|---|---|
| CVE-2026-76504 A vulnerability in the API session-based authentication management of Cisco Catalyst SD-WAN Manager could allow an unauthenticated, remote attacker to access… | Critical Known exploited | Same weakness, CWE-177 |
| GHSA-jqff-g426-hqxp fast-uri vulnerable to host confusion via percent-encoded scheme normalization | High | Same weakness, CWE-177 |
| GHSA-q5qw-h33p-qvwr Hono vulnerable to arbitrary file access via serveStatic vulnerability | Critical | Same weakness, CWE-177 |
| GHSA-fvhj-4qfh-q2hm Traefik incorrectly processes fragment in the URL, leads to Authorization Bypass | Medium | Same weakness, CWE-177 |
| GHSA-g8q8-fggx-9r3q Keycloak vulnerable to path traversal via double URL encoding | Critical | Same weakness, CWE-177 |
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