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Node.js Adapter for Hono: Path traversal in `serve-static` on Windows via encoded backslash (`%5C`)GHSA-frvp-7c67-39w9

MEDIUMFix: honojs/node-server@cd076e1

GHSA-frvp-7c67-39w9 is a medium-severity (CVSS 5.9) vulnerability in @hono/node-server. A fix is available for @hono/node-server — see the affected versions and patch details below.

Published
Updated
Affected
2 pkgs
Patched
2 / 2
Exploits
None indexed
Exploitation data as of Sep 10, 2026 · OSV.dev, FIRST.org (EPSS)

Real-World Exposure

2 pkgs affected

How broadly this vulnerability is actually deployed: weekly install volume shows current usage, and reverse-dependency count shows how many other packages break if it stays unpatched.

4Kother npm packages depend on this — each one inherits the vulnerability until it's patched upstream
@hono/node-servernpm
96.8Mdownloads / week

Description

The same as the hono core Path traversal in serve-static on Windows via encoded backslash (%5C).

Summary

On Windows hosts, an encoded backslash (%5C) in the request path decodes to \, which the Windows path resolver treats as a separator. serve-static then resolves a single URL segment such as admin\secret.txt into a nested file under the root and serves it, letting an attacker read static files meant to be protected behind prefix-mounted middleware. Directory escape (..) remains blocked.

Details

The router splits paths only on /, so /admin%5Csecret.txt is one segment and middleware on /admin/* does not run. The serve-static guard rejects ./.. and consecutive separators but lets a lone \ through; on Windows the file resolver re-splits it into the protected subtree.

This affects Windows hosts serving static files via the Node, Bun, or Deno adapters that guard a static subtree with prefix-mounted middleware.

Impact

An unauthenticated attacker can read static files under a middleware-guarded prefix on Windows hosts. The read stays within the configured root; escape outside the root is not possible.

Affected Packages

2 total 2 fixed
EcosystemPackageVulnerable rangeFix
📦npm@hono/node-server≥ 2.0.0&&< 2.0.52.0.5npm install @hono/node-server@2.0.5
📦npm@hono/node-serverall versions1.19.15npm install @hono/node-server@1.19.15

Detection & mitigation playbook

Open-source dependency

  1. Detect

    Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for @hono/node-server, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

  2. Fix

    Update @hono/node-server to 2.0.5 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-frvp-7c67-39w9 is resolved across your whole dependency graph.

  3. Workarounds

    Resolve every user-supplied path to its canonical form and reject anything that escapes the intended directory, and run the component under an account that has no read or write access outside the directory it legitimately serves.

Frequently Asked Questions

The same as the `hono` core [Path traversal in `serve-static` on Windows via encoded backslash (`%5C`)](https://github.com/honojs/hono/security/advisories/GHSA-wwfh-h76j-fc44). ### Summary On Windows hosts, an encoded backslash (`%5C`) in the request path decodes to `\`, which the Windows path resolver treats as a separator. `serve-static` then resolves a single URL segment such as `admin\secret.txt` into a nested file under the root and serves it, letting an attacker read static files meant to be protected behind prefix-mounted middleware. Directory escape (`..`) remains blocked. ### Detai
O3 Security · Impact-Aware SCA

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Node.js Adapter for Hono: Path traversal in `serve-static`…