dbcve.org
HonoApplication

CVE-2026-47676

MEDIUM · 5.3 CVSS v3.1 Published 2026-05-28
Fix available
A fix is available. Upgrade to 4.12.21 or later.
See remediation →
62/100
Remediation priority · Elevated
Remotely reachable No privileges Zero-click

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 · unedited
Hono is a Web application framework that provides support for any JavaScript runtime. Prior to 4.12.21, app.mount() strips the mount prefix from the incoming request path using the raw URL pathname, while route matching is performed against the percent-decoded path. This inconsistency causes the prefix to be stripped at the wrong position when the path contains percent-encoded multi-byte characters, resulting in the mounted sub-application receiving an incorrect path. This vulnerability is fixed in 4.12.21.

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 confidence

In Hono prior to 4.12.21, the app.mount() function strips the mount prefix from incoming request paths using the raw URL pathname, while route matching is performed against the percent-decoded path. When a path contains percent-encoded multi-byte characters (e.g., UTF-8 characters), this inconsistency causes the prefix to be stripped at the wrong position, resulting in the mounted sub-application receiving an incorrect or malformed path.

MitigationUpgrade Hono to version 4.12.21 or later. Applications using app.mount() with paths that may contain percent-encoded characters should test that mounted sub-applications receive the correct path after the upgrade.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

NVD · CPE data
HonoApplication
Affected:< 4.12.21

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
Low
Privileges
None
User interaction
None
Scope
Unchanged
Confidentiality
Low
Integrity
None
Availability
None

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/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 checks

Work through these to decide whether this CVE applies to you.

  1. Check your Hono version
    Run `npm list hono` or check your package.json dependencies to identify the installed version of the Hono framework.
    Affected if The installed version is lower than 4.12.21 (the fixed version). Compare your version against the affected range of < 4.12.21.
  2. Identify app.mount() usage
    Search your codebase for occurrences of `app.mount(` or `.mount(` to determine if your application uses the mount functionality.
    Affected if Your code contains app.mount() calls that mount sub-applications to specific path prefixes.
  3. Examine mount path parameters
    Review the path arguments passed to app.mount() calls. Look for static mount paths or dynamic paths that could receive user-supplied values.
    Affected if Mount paths include or could receive percent-encoded characters, particularly multi-byte UTF-8 characters (e.g., non-ASCII characters, international text).
  4. Inspect request path handling
    If possible, add logging in your mounted sub-application to inspect the incoming request path it receives. Compare the received path against what was originally requested.
    Affected if The mounted sub-application receives a path that differs from the expected path after the mount prefix is stripped, indicating incorrect path normalization.

You are affected if you are running Hono version lower than 4.12.21 AND using app.mount() with paths that contain or could contain percent-encoded multi-byte characters, resulting in the mounted sub-application receiving malformed paths.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

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 · scoped
Upgrade available Upgrade to 4.12.21 or later
Fixed in 4.12.21
Interim mitigation

Upgrade Hono to version 4.12.21 or later. Applications using app.mount() with paths that may contain percent-encoded characters should test that mounted sub-applications receive the correct path after the upgrade.

Recommended fix High confidence

4.12.21

  1. Check your current Hono version by running `npm list hono` or looking at your package.json
  2. Update Hono to version 4.12.21 or later by running `npm install hono@^4.12.21` or `npm update hono`
  3. Verify the installation was successful by running `npm list hono` and confirming the version is 4.12.21 or higher
  4. Test your application's mounted routes, particularly those with percent-encoded characters in paths, to confirm the fix works correctly

Generated from the published advisory — verify against the referenced sources before acting.

Fix this in Hono Scoped from the published advisory
  • Consultation1.0 h
  • Implementation1.0 h
  • Testing2.0 h
  • Review / QA1.0 h
5.0 hours of engineering $860
Get the upgrade done

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $1,376.

Scan for this in your stack

Free · runs locally
dbcve dependency scanner

Check whether your project pulls in CVE-2026-47676 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.

Get it on GitHub Scan in the browser

References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2026-47676 in production — separate from our analysis above.

No notes yet

Be the first to add a field note for this CVE — a mitigation you’ve verified, a version caveat, or a link to a working fix. Sign in above to contribute.

What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
  • Verified mitigations, workarounds, and config changes
  • Version or environment caveats, and links to real fixes
  • No weaponised exploit code, or anything meant to cause harm
  • No spam, self-promotion, credentials, or personal data