CVE-2026-39407 is a medium-severity (CVSS 5.3) Path Traversal vulnerability in hono. A fix is available for hono — see the affected versions and patch details below.
Hono has a middleware bypass via repeated slashes in serveStatic
Exploitation Status
No confirmed exploitation observed yet
- CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
- 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-2026-39407.
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
Where this sits among everything scored
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
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.
Details
The routing layer and serveStatic handle repeated slashes differently.
For example:
/admin/secret.txt => matches /admin/*
/admin//secret.txt => may not match /admin/*
However, serveStatic may interpret both paths as the same file location (e.g., admin/secret.txt) and return the file.
This inconsistency allows a request such as:
GET //admin/secret.txt
to bypass middleware registered on /admin/* and access protected files.
The issue has been fixed by rejecting paths that contain repeated slashes, ensuring consistent behavior between route matching and static file resolution.
Impact
An attacker can access static files that are intended to be protected by route-based middleware by using repeated slashes in the request path.
This can lead to unauthorized access to sensitive files under the static root.
This issue affects applications that rely on serveStatic together with route-based middleware for access control.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 📦npm | hono | all versions | 4.12.12npm install hono@4.12.12 |
Affected Products
honohonoDetection & 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 4.12.12 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-39407 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-2026-39407 in your dependencies?
Find it across npm, including transitive dependencies.