@fastify/static versions 8.0.0 through 9.1.0 decode percent-encoded path separators (%2F) before filesystem resolution, while Fastify's…
openjs·CWE-177·Published 2026-04-16
@fastify/static versions 8.0.0 through 9.1.0 decode percent-encoded path separators (%2F) before filesystem resolution, while Fastify's router treats them as literal characters. This mismatch allows attackers to bypass route-based middleware or guards that protect files served by @fastify/static. For example, a route guard on a protected path can be circumvented by encoding the path separator in the URL. Upgrade to @fastify/static 9.1.1 to fix this issue. There are no workarounds.
@fastify/static versions 8.0.0 through 9.1.0 decode percent-encoded path separators (%2F) before filesystem resolution, while Fastify's router treats them as literal characters. This mismatch allows attackers to bypass route-based middleware or guards that protect files served by @fastify/static. For example, a route guard on a protected path can be circumvented by encoding the path separator in the URL. Upgrade to @fastify/static 9.1.1 to fix this issue. There are no workarounds.
### 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.
### 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.
| Version | Type | Source | Base | Exp | Impact | Vector |
|---|---|---|---|---|---|---|
| 3.1 | Primary | cve.org | 5.9 | — | — | CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N |
| 3.1 | Secondary | NVD | 5.9 | 2.2 | 3.6 | CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N |
| 3.1 | Secondary | GHSA | 5.9 | — | — | CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N |