CVE-2026-39407 Hono has a middleware bypass via repeated slashes in serveStatic
Attackers can bypass route-based authorization middleware to access protected static files by using repeated slashes in request paths.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-39407?
CVE-2026-39407 is a medium-severity missing authorization vulnerability in honojs hono, published on 8 Apr 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 4.12.12, a path handling inconsistency in serveStatic allows protected static files to be accessed by using repeated slashes (//) in the request path. When route-based middleware (e.g., /admin/*) is used for authorization, the router may not match paths containing repeated slashes, while serveStatic resolves them as normalized paths. This can lead to a middleware bypass. This vulnerability is fixed in 4.12.12.
Weakness: CWE-22
Which versions are affected by CVE-2026-39407?
2 open source packages ship an affected version, including hono. It affects 1 product.
| Package | Affected | Fixed in |
|---|---|---|
hono npm | All versions | 4.12.12 |
hono npm | All versions | 4.12.12 |
Products include Hono Hono.
How do I fix CVE-2026-39407?
Upgrade hono to 4.12.12 or later.
Upgrade, and check permissions on every request on the server, not only in the interface. More about Missing authorization.
Is CVE-2026-39407 being exploited?
There is no known exploitation of CVE-2026-39407 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-PI04588, CLEANSTART-2026-QM34993, GHSA-wmmm-f939-6g9c, MINI-5gg9-7cgg-fwc7, MINI-9rcg-gqj8-7qq6, MINI-ch98-5rh5-5r6r and 5 more.