CVE-2026-54286: hono Path Traversal Vulnerability

MODERATE
Advisory Identifier: GHSA-wwfh-h76j-fc44
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CVSS 5.9
CWE-22
Published
Advisory Summary

CVE-2026-54286 is a MODERATE (CVSS 5.9) path traversal vulnerability (CWE-22: Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal')) affecting hono libraries in the npm ecosystem. The issue involves path traversal in `serve-static` on windows via encoded backslash (`%5c`). Remediation is available by upgrading affected packages to version 4.12.25.

CVE-2026-54286 at a Glance

CVE Identifier CVE-2026-54286
GHSA Identifier GHSA-wwfh-h76j-fc44
Severity MODERATE
CVSS v3.1 Base Score 5.9
CWE Classification CWE-22: Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal')
Affected Product hono
Package Ecosystem npm
Published Date
Last Updated

Security Impact

CVSS: 5.9

The security impact metrics below are parsed directly from the CVSS v3.1 vector string (CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N).

Attack Vector Network (AV:N)
Attack Complexity High (AC:H)
Privileges Required None (PR:N)
User Interaction None (UI:N)
Scope Unchanged (S:U)
Confidentiality High (C:H)
Integrity None (I:N)
Availability None (A:N)

How to Fix CVE-2026-54286

To remediate this vulnerability, upgrade all affected hono dependencies to a patched release. Both direct and transitive dependencies should be checked, as frameworks or security libraries may pull in vulnerable versions transitively.

hono fixed: 4.12.25 
npm install hono@4.12.25
Verify Direct and Transitive Dependencies

Run the following command in your project directory to verify that all resolved dependencies use the patched release: 

npm ls hono

How to Check if You Are Affected

To determine whether your Node.js application is affected by CVE-2026-54286, inspect your project dependencies using npm:

npm ls hono

Analyze the terminal output to locate any version of hono in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 4.12.25), your application is affected.

Note: The npm ls hono command inspects dependencies declared in your package.json and lockfile; it does not perform automated runtime dynamic scanning.

Technical Details

Vulnerability Mechanism & Technical Analysis

This vulnerability is classified under CWE-22: Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal'), where the product uses external input to construct a pathname that is intended to identify a file or directory that is located underneath a restricted parent directory, but the product does not properly neutralize special elements within the pathname that can cause the pathname to resolve to a location that is outside of the restricted directory. In hono, software state validation or input boundaries are circumvented during processing. Review the official source advisory statement below for specific affected components, classes, and reproduction details.

Source Advisory Statement

### 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 is not possible.

CVE-2026-54286 Affected hono Versions

1 component(s)
Fixed Versions:
4.12.25
Product / Package Ecosystem Affected Versions Fixed Version
hono
npm/hono
npm
< 4.12.25
4.12.25

References

GitHub Advisory / Wiki ADVISORY
https://github.com/honojs/hono/security/advisories/GHSA-wwfh-h76j-fc44
NVD — CVE-2026-54286 NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-54286
hono Source Repository REPOSITORY
https://github.com/honojs/hono

Frequently Asked Questions

What is CVE-2026-54286?
CVE-2026-54286 is a security vulnerability in hono involving Path traversal in `serve-static` on Windows via encoded backslash (`%5C`) under CWE-22: Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal').
Which hono versions are affected?
Affected versions include releases prior to 4.12.25 across affected packages: hono.
What version fixes CVE-2026-54286?
Upgrading to 4.12.25 (or the latest patched release for your respective branch) resolves the vulnerability.
Is hono affected?
Yes, hono is affected in releases prior to 4.12.25. Upgrade your dependency to 4.12.25 or later.
What is the CVSS score of CVE-2026-54286?
CVE-2026-54286 has a CVSS v3.1 base score of 5.9 (MODERATE) with vector string CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N.
What CWE is associated with CVE-2026-54286?
CVE-2026-54286 is classified under CWE-22: Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal') (The product uses external input to construct a pathname that is intended to identify a file or directory that is located underneath a restricted parent directory, but the product does not properly neutralize special elements within the pathname that can cause the pathname to resolve to a location that is outside of the restricted directory.).
How can I check npm dependencies for CVE-2026-54286?
Run the dependency tree command: 'npm ls hono'. This command lists direct and transitive dependencies in your build configuration so you can verify if a vulnerable version is resolved.
Machine-readable OSV JSON OSV v1.5 Schema
Normalized schema output
View Raw JSON 
{
  "schema_version" : "1.4.0",
  "id" : "GHSA-wwfh-h76j-fc44",
  "modified" : "2026-07-21T15:27:07Z",
  "published" : "2026-06-16T14:09:03Z",
  "aliases" : [ "CVE-2026-54286" ],
  "summary" : "hono: Path traversal in `serve-static` on Windows via encoded backslash (`%5C`)",
  "details" : "### Summary\n\nOn 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.\n\n### Details\n\nThe 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.\n\nThis affects Windows hosts serving static files via the Node, Bun, or Deno adapters that guard a static subtree with prefix-mounted middleware.\n\n### Impact\n\nAn 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 is not possible.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "npm",
      "name" : "hono"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "4.12.25"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/honojs/hono/security/advisories/GHSA-wwfh-h76j-fc44"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-54286"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/honojs/hono"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-22" ],
    "severity" : "MODERATE",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-06-16T14:09:03Z",
    "nvd_published_at" : "2026-06-22T18:16:47Z"
  }
}