CVE-2026-39406 is a medium-severity (CVSS 5.3) Path Traversal vulnerability in @hono/node-server. A fix is available for @hono/node-server — see the affected versions and patch details below.
@hono/node-server 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-2026-39406.
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
How urgent is this, really
CVE-2026-39406 plotted by exploitation likelihood (EPSS) against impact (CVSS). The shaded corner — EPSS 50%+ and CVSS 7.0+ — is where this CVE doesn't sit, though severity or exploitability alone can still warrant action.
Where this sits among everything scored
Of 378,567 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Real counts from FIRST.org, not a sample — log-scaled since the landscape is heavily right-skewed.
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.
@hono/node-servernpmDescription
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/*
This inconsistency allows a request such as:
GET //admin/secret.txt
to bypass middleware registered on /admin/* and access protected files.
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/node-server | all versions | 1.19.13npm install @hono/node-server@1.19.13 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for @hono/node-server, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update @hono/node-server to 1.19.13 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-39406 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like CVE-2026-39406 can be triaged on real exposure rather than presence alone.
Tailored to CVE-2026-39406. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is CVE-2026-39406 in your dependencies?
O3 Security finds CVE-2026-39406 across npm dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.