CVE-2026-84365 is a medium-severity (CVSS 6.5) Path Traversal vulnerability in hono. A fix is available for hono — see the affected versions and patch details below.
Hono: Incomplete fix for CVE-2026-39408: `toSSG()` still writes files outside the output directory
Exploitation Status
No confirmed exploitation observed yet
- CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.
Exploitation and automatability from CISA’s SSVC triage for CVE-2026-84365.
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
CVE-2026-84365 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.
Where this sits among everything scored
Of 395,249 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Counts from FIRST.org, log-scaled.
Real-World Exposure
How broadly this vulnerability is actually deployed: weekly install volume shows current usage, and reverse-dependency count shows how many other packages break if it stays unpatched.
hononpmDescription
Summary
The fix released for CVE-2026-39408 does not cover every traversal sequence. toSSG() can still write files outside the configured output directory when a route parameter contains consecutive parent-directory segments.
Details
Static site generation builds each output path from the route path and the values supplied through ssgParams, then verifies that the result stays inside the output directory. That check normalizes the path with the same routine that built it, and the routine did not fully collapse runs of consecutive parent-directory segments. A value carrying enough of them produces a path the check accepts, but the filesystem resolves outside the output directory.
The earlier fix handled a single parent-directory segment, so it blocks the sequence reported at the time while leaving longer runs unhandled. The check also treated output directories that differ only 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 — slugs coming from a CMS, an API, or user submissions.
Impact
A value reaching ssgParams from an untrusted source can cause build output to be written outside the intended output directory, carrying whatever content the route handler produced.
This may lead to:
- files being created or overwritten elsewhere in the build environment
- generated artifacts or deployment output being altered
This affects build-time static site generation only; request-time routing is not affected. Applications whose ssgParams values are entirely developer-controlled are not affected.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 📦npm | hono | all versions | 4.13.5npm install hono@4.13.5 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for hono, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update hono to 4.13.5 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-84365 is resolved across your whole dependency graph.
Workarounds
Resolve every user-supplied path to its canonical form and reject anything that escapes the intended directory, and run the component under an account that has no read or write access outside the directory it legitimately serves.
Frequently Asked Questions
Is CVE-2026-84365 in your dependencies?
Find it across npm, including transitive dependencies.