Hono: Middleware bypass via repeated slashes in serveStatic

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

5.3 · CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N

EPSS

• CVE-2026-39407: 0.46% estimated exploitation activity in the next 30 days; percentile 39.83 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

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: 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: 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…

Published by the source

8 Apr 2026, 00:16 UTC

Last modified by the source

10 Sep 2026, 03:50 UTC

Source last checked

26 Oct 2026, 12:47 UTC

1. Revision 2 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-wmmm-f939-6g9c

2. Revision 1 · created · 24 Oct 2026

   Published from osv record GHSA-wmmm-f939-6g9c

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# Patch Next advisory brief: CVE-2026-39407

Advisory: Hono: Middleware bypass via repeated slashes in serveStatic
IDs: CVE-2026-39407, GHSA-wmmm-f939-6g9c
Record: https://patchnext.com/advisories/cve-2026-39407 (revision 2, source checked 26 Oct 2026, 12:47 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 5.3)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: hono 4.12.12. A vendor fix does not mean a deployment is fixed.

## Affected components
- npm hono: affected < 4.12.12; fixed in 4.12.12

## Suggested inspection (read-only)
- `npm ls hono --all`: lists every installed copy and version, including transitive ones. Run in the project root after `npm ci`.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on hono.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://osv.dev/vulnerability/GHSA-wmmm-f939-6g9c (OSV record GHSA-wmmm-f939-6g9c lists affected ranges: npm hono >=0 <4.12.12 (fixed))
- Verified: https://github.com/advisories/GHSA-wmmm-f939-6g9c (GitHub-reviewed advisory GHSA-wmmm-f939-6g9c lists affected ranges: npm hono >=0 <4.12.12)

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