---
id: CVE-2026-54286
aliases:
  - GHSA-wwfh-h76j-fc44
title: >-
  hono: Path traversal in `serve-static` on Windows via encoded backslash
  (`%5C`)
summary: >-
  hono: Path traversal in `serve-static` on Windows via encoded backslash
  (`%5C`)
severity: medium
cvss: 5.9
cwe:
  - CWE-22
vendor: hono
product: hono
ecosystem: npm
affected:
  - hono < 4.12.25
patched:
  - hono 4.12.25
published: '2026-06-16'
updated: '2026-06-16'
source: GHSA
sourceUrl: 'https://github.com/advisories/GHSA-wwfh-h76j-fc44'
references:
  - url: 'https://github.com/honojs/hono/security/advisories/GHSA-wwfh-h76j-fc44'
  - url: 'https://github.com/advisories/GHSA-wwfh-h76j-fc44'
tags:
  - ghsa
  - npm
epss: 0.00433
epssPercentile: 0.3489
ingestedAt: '2026-07-07T15:41:58.359Z'
---

## Overview

### 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

- `hono < 4.12.25`

## Remediation

Upgrade to a patched release:

- `hono 4.12.25`