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Medium, CVSS 5.9amended

hono: Path traversal in serve-static on Windows via encoded backslash (%5C)

CVE-2026-54286GHSA-wwfh-h76j-fc44

What to do

Vendor fix available. Upgrade each affected package to the fixed version on its release line (hono 4.12.25), redeploy, then verify what is actually installed.

This page has no inventory attached, so it cannot say whether you are affected. A vendor fix is not proof that your deployment is fixed.

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Affected packages

  • npm hono

    Affected
    < 4.12.25
    Fixed in
    4.12.25

Sources

Severity and exploitation
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
  • CVE-2026-54286: 0.43% estimated exploitation activity in the next 30 days; percentile 37.65 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.
Source description

As published by the source; long descriptions are shortened.

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 middleware-guarded prefix on Windows hosts. The read stays within the configured root; escape outside the root…

Dates and revisions
Published by the source
Last modified by the source
Source last checked
  1. Revision 2 · amended ·

    Amended from ghsa record GHSA-wwfh-h76j-fc44

  2. Revision 1 · created ·

    Published from osv record GHSA-wwfh-h76j-fc44

Agent brief

Preview the exact text before you copy it. Commands are read-only suggestions; review them before running anything.

# Patch Next advisory brief: CVE-2026-54286

Advisory: hono: Path traversal in `serve-static` on Windows via encoded backslash (`%5C`)
IDs: CVE-2026-54286, GHSA-wwfh-h76j-fc44
Record: https://patchnext.com/advisories/cve-2026-54286 (revision 2, source checked 26 Oct 2026, 12:57 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 4.12.25. A vendor fix does not mean a deployment is fixed.

## Affected components
- npm hono: affected < 4.12.25; fixed in 4.12.25

## 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-wwfh-h76j-fc44 (OSV record GHSA-wwfh-h76j-fc44 lists affected ranges: npm hono >=0 <4.12.25 (fixed))
- Verified: https://github.com/advisories/GHSA-wwfh-h76j-fc44 (GitHub-reviewed advisory GHSA-wwfh-h76j-fc44 lists affected ranges: npm hono >=0 <4.12.25)

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