# CVE-2026-47676: Hono: app.mount() strips mount prefix using undecoded path, causing incorrect routing for percent-encoded paths

> Attackers can cause incorrect routing in mounted sub-applications by using percent-encoded paths, potentially bypassing intended access controls or logic.

- **Severity:** Medium 5.3 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 28 May 2026
- **Updated:** 28 May 2026
- **Also known as:** ECHO-22d9-65f9-d2a1, GHSA-2gcr-mfcq-wcc3, MINI-44c8-22vw-9qxr, MINI-68j6-g2pc-r6r9, MINI-88gj-fxv3-3rf6, MINI-c296-vr9p-2gfh, MINI-g83v-fwc2-6rmh, MINI-hm7f-43fx-qc95, MINI-j3fj-vq3v-3xh5, MINI-j4x3-p9q7-645m, MINI-q6x6-m858-2vq5, MINI-qc3m-gmq6-7wrh, MINI-v7pw-cxmh-2g6w, ROOT-APP-NPM-CVE-2026-47676

## What is CVE-2026-47676?

CVE-2026-47676 is a medium-severity vulnerability in honojs hono, published on 28 May 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

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.

Weakness: CWE-693 (Protection Mechanism Failure), CWE-444 (Inconsistent Interpretation of HTTP Requests)

## Which versions are affected by CVE-2026-47676?

2 open source packages ship an affected version, including hono. It affects 1 product.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `hono` | npm | All versions | 4.12.21 |
| `hono` | npm | All versions | 4.12.21 |

Products: Hono Hono.

## How do I fix CVE-2026-47676?

Upgrade hono to 4.12.21 or later.

## Is CVE-2026-47676 being exploited?

There is no known exploitation of CVE-2026-47676 in the wild and no public exploit code.

## Other vulnerabilities in honojs hono

- [CVE-2026-27700](https://insights.sbomify.com/CVE-2026-27700/): Hono is Vulnerable to Authentication Bypass by IP Spoofing in AWS Lambda ALB conninfo (high 8.2)
- [CVE-2026-22817](https://insights.sbomify.com/CVE-2026-22817/): JWT Algorithm Confusion via Unsafe Default (HS256) in Hono JWT Middleware Allows Token Forgery and Auth Bypass (high 8.2)
- [CVE-2026-22818](https://insights.sbomify.com/CVE-2026-22818/): JWT algorithm confusion in Hono JWK Auth Middleware when JWK lacks "alg" (untrusted header.alg fallback) (high 8.2)
- [CVE-2025-62610](https://insights.sbomify.com/CVE-2025-62610/): Hono Improperly Authorizes JWT Audience Validation (high 8.1)
- [CVE-2026-29045](https://insights.sbomify.com/CVE-2026-29045/): Hono: Arbitrary file access via serveStatic vulnerability (high 7.5)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-47676 and fix it if it is affected.

What it is: CVE-2026-47676 is a medium-severity vulnerability in honojs hono, published on 28 May 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-47676 in the wild and no public exploit code.

Affected packages and fixed versions:
- hono (npm): affected all versions; fixed in 4.12.21
- hono (npm): affected all versions; fixed in 4.12.21

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-47676/ (Markdown: https://insights.sbomify.com/CVE-2026-47676/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-47676
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-47676
- OSV: https://osv.dev/vulnerability/CVE-2026-47676

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-47676/
Summaries are generated and may contain mistakes; the official description above is the record.