CVE-2026-54286
Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.
NVD · uneditedHono is a Web application framework that provides support for any JavaScript runtime. Prior to 4.12.25, 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. This vulnerability is fixed in 4.12.25.
Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.
dbcve analysis · high confidenceIn Hono's serve-static package prior to 4.12.25, an encoded backslash (%5C) in the request URL path decodes to a literal backslash on Windows systems. Since Windows treats backslash as a path separator, a request for 'admin%5Csecret.txt' resolves to a file nested outside the intended static root directory, enabling path traversal to read protected files.
Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.
CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.
From the vector- Attack vector
- Network
- Complexity
- High
- Privileges
- None
- User interaction
- None
- Scope
- Unchanged
- Confidentiality
- High
- Integrity
- None
- Availability
- None
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N
Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.
dbcve checksWork through these to decide whether this CVE applies to you.
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Identify serve-static package versionRun 'npm list @hono/serve-static' or check package.json dependencies to see the installed version of @hono/serve-staticAffected if The installed version is prior to 4.12.25 (e.g., 4.12.24, 4.12.0, etc.)
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Confirm operating system is WindowsCheck the environment where the Hono application runs: run 'node -e "console.log(process.platform)"' which returns 'win32' on WindowsAffected if The application runs on Windows (process.platform equals 'win32')
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Verify static file serving is enabledInspect your Hono app configuration to confirm serve-static middleware is mounted (look for app.use('/static', serveStatic(...)) or similar pattern)Affected if Static file serving from a root directory is configured and enabled
You are affected if you are running @hono/serve-static version below 4.12.25 on Windows with static file serving enabled, as encoded backslashes in URLs can escape the static root directory.
Generated from the published advisory. Verify against your own configuration.
Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.
dbcve · scopedUpgrade Hono to version 4.12.25 or later which contains the fix for proper handling of encoded backslashes on Windows.
4.12.25
- 1. Identify your current Hono version by checking package.json or running `npm list @hono/node-server` or `pnpm list @hono/node-server`
- 2. Update Hono to version 4.12.25 or later by running `npm install hono@^4.12.25` or `pnpm add hono@^4.12.25`
- 3. If using serve-static explicitly, also ensure @hono/serve-static is updated to match: `npm install @hono/serve-static@latest`
- 4. Rebuild and restart your application
- 5. Test that static file serving works correctly on Windows and non-Windows hosts
- 6. Verify that path traversal via encoded backslashes (%5C) is now blocked - request paths containing %5C should return 404 or be sanitized
Generated from the published advisory — verify against the referenced sources before acting.
- Consultation1.0 h
- Implementation1.0 h
- Testing2.0 h
- Review / QA1.0 h
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Free · runs locallyCheck whether your project pulls in CVE-2026-54286 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.
References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.
Primary sourcesPractitioner notes
ContributedPeer-ranked notes from engineers who’ve handled CVE-2026-54286 in production — separate from our analysis above.
The advisory tells you what broke. It rarely tells you what actually worked. If you’ve dealt with this one, that detail is what the next engineer is searching for.
- The version that genuinely resolved it — not the one the vendor claimed
- A config change or rule that shut the vector down
- A gotcha in the upgrade path that cost you an afternoon
No notes yet
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- Version or environment caveats, and links to real fixes
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