CVE-2026-84365 Hono: Incomplete fix for CVE-2026-39408: `toSSG()` still writes files outside the output directory
Attackers can write files outside the output directory during static site generation if route parameters are untrusted, potentially altering deployment artifacts.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- A user has to click or open something
- Fix
- Available
What is CVE-2026-84365?
CVE-2026-84365 is a medium-severity path traversal vulnerability in honojs hono, published on 1 Sep 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.
Official description
Hono is a Web application framework that provides support for any JavaScript runtime. From 4.12.12 until 4.13.5, the fix released for CVE-2026-39408 does not cover every traversal sequence, and toSSG() can still write files outside the configured output directory when a route parameter contains consecutive parent-directory segments. Static site generation builds each output path from the route path and values supplied through ssgParams, then verifies that the result stays inside the output directory using the same normalization routine that built the path. That routine does not fully collapse runs of consecutive parent-directory segments, allowing a path that the check accepts to resolve outside the output directory, and the check also treats output directories that differ in how they are rooted as equivalent. This arises when an application generates a static site from route parameter values it does not fully control, such as slugs from a CMS, API, or user submission. An untrusted ssgParams value can create or overwrite files elsewhere in the build environment and alter generated artifacts or deployment output. The vulnerability affects build-time static site generation only; request-time routing and applications with entirely developer-controlled ssgParams values are not affected. This issue is fixed in version 4.13.5.
Weakness: CWE-22
Which versions are affected by CVE-2026-84365?
2 open source packages ship an affected version, including hono.
| Package | Affected | Fixed in |
|---|---|---|
hono npm | All versions | 4.13.5 |
hono npm | All versions | 4.13.5 |
How do I fix CVE-2026-84365?
Upgrade hono to 4.13.5 or later.
Upgrade, and resolve every user-supplied path against an allowed base folder before opening it. More about Path traversal.
Is CVE-2026-84365 being exploited?
There is no known exploitation of CVE-2026-84365 in the wild and no public exploit code.
Sources
Also known as CLEANSTART-2026-UQ77202, ECHO-a753-f273-abba, GHSA-gqvv-2mrq-wpjv, MINI-5qpr-7mqh-mh78, MINI-629w-9c48-v78m, MINI-6jxh-5vgh-6f7w and 5 more.