# CVE-2026-39408: Hono has a path traversal in toSSG() allows writing files outside the output directory

> Attackers can write files outside the intended output directory during static site generation using crafted dynamic route parameters in Hono.

- **Severity:** Medium 5.9 (`CVSS:4.0/AV:L/AC:H/AT:P/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 8 Apr 2026
- **Updated:** 10 Apr 2026
- **Also known as:** CLEANSTART-2026-BO90613, CLEANSTART-2026-FT94071, GHSA-xf4j-xp2r-rqqx, MINI-3324-w2w9-v95f, MINI-3jvg-wcg2-r32h, MINI-6r4g-m2p5-hxhm, MINI-gmq3-6v89-cc2j, MINI-wfgw-fxgc-3hqf, MINI-wmjx-f2gp-vm9w, MINI-wv7v-r7hw-2hv9

## What is CVE-2026-39408?

CVE-2026-39408 is a medium-severity path traversal vulnerability in honojs hono, published on 8 Apr 2026. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

Hono is a Web application framework that provides support for any JavaScript runtime. Prior to 4.12.12, a path traversal issue in toSSG() allows files to be written outside the configured output directory during static site generation. When using dynamic route parameters via ssgParams, specially crafted values can cause generated file paths to escape the intended output directory. This vulnerability is fixed in 4.12.12.

Weakness: CWE-22 (Improper Limitation of a Pathname to a Restricted Directory)

## Which versions are affected by CVE-2026-39408?

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


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `hono` | npm | From 4.0.0 | 4.12.12 |
| `hono` | npm | From 4.0.0 | 4.12.12 |

Products: Hono Hono.

## How do I fix CVE-2026-39408?

Upgrade hono to 4.12.12 or later.

## Is CVE-2026-39408 being exploited?

There is no known exploitation of CVE-2026-39408 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-2026-39408 and fix it if it is affected.

What it is: CVE-2026-39408 is a medium-severity path traversal vulnerability in honojs hono, published on 8 Apr 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-39408 in the wild and no public exploit code.

Affected packages and fixed versions:
- hono (npm): affected from 4.0.0; fixed in 4.12.12
- hono (npm): affected from 4.0.0; fixed in 4.12.12

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-2026-39408/ (Markdown: https://insights.sbomify.com/CVE-2026-39408/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-39408
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-39408
- OSV: https://osv.dev/vulnerability/CVE-2026-39408

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-39408/
Summaries are generated and may contain mistakes; the official description above is the record.