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.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
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
Which versions are affected by CVE-2026-39408?
2 open source packages ship an affected version, including hono. It affects 1 product.
| Package | Affected | Fixed in |
|---|---|---|
hono npm | From 4.0.0 | 4.12.12 |
hono npm | From 4.0.0 | 4.12.12 |
Products include Hono Hono.
How do I fix CVE-2026-39408?
Upgrade hono to 4.12.12 or later.
Upgrade, and resolve every user-supplied path against an allowed base folder before opening it. More about Path traversal.
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 Hono is Vulnerable to Authentication Bypass by IP Spoofing in AWS Lambda ALB conninfo
- CVE-2026-22817 JWT Algorithm Confusion via Unsafe Default (HS256) in Hono JWT Middleware Allows Token Forgery and Auth Bypass
- CVE-2026-22818 JWT algorithm confusion in Hono JWK Auth Middleware when JWK lacks "alg" (untrusted header.alg fallback)
- CVE-2025-62610 Hono Improperly Authorizes JWT Audience Validation
- CVE-2026-29045 Hono: Arbitrary file access via serveStatic vulnerability
Sources
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 and 4 more.