Node.js Adapter for Hono: Path traversal in serve-static on Windows via encoded backslash (%5C)

Exploitation

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

CVSS

5.9 · CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N

EPSS

No dated EPSS signal available.

As published by the source; long descriptions are shortened.

The same as the hono core Path traversal in serve-static on Windows via encoded backslash (%5C). Summary On Windows hosts, an encoded backslash (%5C) in the request path decodes to \, which the Windows path resolver treats as a separator. serve-static then resolves a single URL segment such as admin\secret.txt into a nested file under the root and serves it, letting an attacker read static files meant to be protected behind prefix-mounted middleware. Directory escape (..) remains blocked. Details The router splits paths only on /, so /admin%5Csecret.txt is one segment and middleware on /admin/ does not run. The serve-static guard rejects ./.. and consecutive separators but lets a lone \ through; on Windows the file resolver re-splits it into the protected subtree. This affects Windows hosts serving static files via the Node, Bun, or Deno adapters that guard a static subtree with prefix-mounted middleware. Impact An unauthenticated attacker can read static files under a…

Published by the source

21 Jul 2026, 18:17 UTC

Last modified by the source

10 Sep 2026, 03:50 UTC

Source last checked

26 Oct 2026, 13:01 UTC

1. Revision 2 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-frvp-7c67-39w9

2. Revision 1 · created · 24 Oct 2026

   Published from osv record GHSA-frvp-7c67-39w9

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# Patch Next advisory brief: GHSA-frvp-7c67-39w9

Advisory: Node.js Adapter for Hono: Path traversal in `serve-static` on Windows via encoded backslash (`%5C`)
IDs: GHSA-frvp-7c67-39w9
Record: https://patchnext.com/advisories/ghsa-frvp-7c67-39w9 (revision 2, source checked 26 Oct 2026, 13:01 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 5.9)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: @hono/node-server 2.0.5, 1.19.15. A vendor fix does not mean a deployment is fixed.

## Affected components
- npm @hono/node-server: affected >= 2.0.0, < 2.0.5; < 1.19.15; fixed in 1.19.15, 2.0.5

## Suggested inspection (read-only)
- `npm ls @hono/node-server --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/node-server.
- 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-frvp-7c67-39w9 (OSV record GHSA-frvp-7c67-39w9 lists affected ranges: npm @hono/node-server >=2.0.0 =0 <1.19.15 (fixed))
- Verified: https://github.com/advisories/GHSA-frvp-7c67-39w9 (GitHub-reviewed advisory GHSA-frvp-7c67-39w9 lists affected ranges: npm @hono/node-server >=2.0.0 =0 <1.19.15)

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