Hono is a Web application framework that provides support for any JavaScript runtime. Prior to 4.12.25, 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. This vulnerability is fixed in 4.12.25.
PUBLISHED5.2CWE-22
Hono: Path traversal in `serve-static` on Windows via encoded backslash (`%5C`)
Problem type
Affected products
honojs
hono
< 4.12.25 - AFFECTED
References
GitHub Security Advisories
GHSA-wwfh-h76j-fc44
hono: Path traversal in `serve-static` on Windows via encoded backslash (`%5C`)
https://github.com/advisories/GHSA-wwfh-h76j-fc44Summary
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.
JSON source
https://cveawg.mitre.org/api/cve/CVE-2026-54286Click to expand
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"assignerShortName": "GitHub_M",
"dateUpdated": "2026-06-22T17:14:40.133Z",
"dateReserved": "2026-06-12T17:46:37.292Z",
"datePublished": "2026-06-22T17:14:40.133Z",
"state": "PUBLISHED"
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"dateUpdated": "2026-06-22T17:14:40.133Z"
},
"title": "Hono: Path traversal in `serve-static` on Windows via encoded backslash (`%5C`)",
"descriptions": [
{
"lang": "en",
"value": "Hono is a Web application framework that provides support for any JavaScript runtime. Prior to 4.12.25, 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. This vulnerability is fixed in 4.12.25."
}
],
"affected": [
{
"vendor": "honojs",
"product": "hono",
"versions": [
{
"version": "< 4.12.25",
"status": "affected"
}
]
}
],
"problemTypes": [
{
"descriptions": [
{
"lang": "en",
"description": "CWE-22: Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal')",
"cweId": "CWE-22",
"type": "CWE"
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}
],
"references": [
{
"url": "https://github.com/honojs/hono/security/advisories/GHSA-wwfh-h76j-fc44",
"name": "https://github.com/honojs/hono/security/advisories/GHSA-wwfh-h76j-fc44",
"tags": [
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"metrics": [
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"cvssV3_1": {
"version": "3.1",
"vectorString": "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N",
"attackVector": "NETWORK",
"attackComplexity": "HIGH",
"privilegesRequired": "NONE",
"userInteraction": "NONE",
"scope": "UNCHANGED",
"confidentialityImpact": "HIGH",
"integrityImpact": "NONE",
"availabilityImpact": "NONE",
"baseScore": 5.9,
"baseSeverity": "MEDIUM"
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}
}