Medium
Hono: Server-Side XSS via JSX Escaping Bypass in cx() Utility
Type: advisorySources: OSV
Hono is a Web application framework that provides support for any JavaScript runtime. From 4.0.0 before 4.12.27, cx() in hono/css composes class names from plain strings but marks the result as already escaped without HTML-escaping the input, allowing untrusted className values used in a JSX class attribute during server-side rendering to break out of the attribute and inject arbitrary markup. This issue is fixed in version 4.12.27.
- Products
- Not specified
- Affected versions
- Not specified
- Fixed versions
- Not specified
- CVEs
- CVE-2026-59895
- Confirmed fixed CVEs
- Not specified
- Updated in this feed
- 4 Nov 2026, 13:22 UTC · Revision 1
Source evidence
Hono: Server-Side XSS via JSX Escaping Bypass in cx() Utility
core-osv · Original sourcePublished 8 Jul 2026, 16:09 UTC
Hono is a Web application framework that provides support for any JavaScript runtime. From 4.0.0 before 4.12.27, cx() in hono/css composes class names from plain strings but marks the result as already escaped without HTML-escaping the input, allowing untrusted className values used in a JSX class attribute during server-side rendering to break out of the attribute and inject arbitrary markup. This issue is fixed in version 4.12.27.
osv:CVE-2026-59895
Complete source record
{
"id": "b2174c06ab1e4afce6d864dced8a3d84d02821fcba7950456b1cb5b4dbdc17ef",
"url": "https://osv.dev/vulnerability/CVE-2026-59895",
"method": "structured",
"payload": {
"kind": "advisory",
"title": "Hono: Server-Side XSS via JSX Escaping Bypass in cx() Utility",
"summary": "Hono is a Web application framework that provides support for any JavaScript runtime. From 4.0.0 before 4.12.27, cx() in hono/css composes class names from plain strings but marks the result as already escaped without HTML-escaping the input, allowing untrusted className values used in a JSX class attribute during server-side rendering to break out of the attribute and inject arbitrary markup. This issue is fixed in version 4.12.27.",
"evidence": "osv:CVE-2026-59895",
"products": [],
"severity": "medium",
"structured": {
"id": "CVE-2026-59895",
"aliases": [
"CVE-2026-59895",
"GHSA-w62v-xxxg-mg59"
],
"metrics": [
{
"type": "CVSS_V3",
"score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N"
}
],
"affected": [
{
"ranges": [
{
"repo": "https://github.com/honojs/hono",
"type": "GIT",
"events": [
{
"introduced": "ca6f36511094522b84b6575d99bde4728bcea87c"
},
{
"fixed": "97c6fe1f12298c715eb7b2da65b4b6e0d81682bb"
},
{
"fixed": "cd3f6f7194f0e5c9d4b26ae0cf232018d0f388fc"
}
],
"database_specific": {
"extracted_events": [
{
"cpe": "cpe:2.3:a:hono:hono:*:*:*:*:*:node.js:*:*",
"range": [
{
"introduced": "4.0.0"
},
{
"fixed": "4.12.27"
}
],
"source": "CPE_RANGE"
},
{
"range": [
{
"fixed": "cd3f6f7194f0e5c9d4b26ae0cf232018d0f388fc"
}
],
"source": "REFERENCES_COMMIT"
},
{
"range": [
{
"fixed": "97c6fe1f12298c715eb7b2da65b4b6e0d81682bb"
}
],
"source": "REFERENCES_TAG",
"original_tag": "v4.12.27"
}
]
}
}
],
"versions": [
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"v4.12.25",
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],
"database_specific": {
"source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-59895.json"
}
}
],
"modified": "2026-10-28T02:30:35.559935508Z",
"provider": "osv",
"references": [
"https://github.com/honojs/hono/releases/tag/v4.12.27",
"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/59xxx/CVE-2026-59895.json",
"https://github.com/honojs/hono/security/advisories/GHSA-w62v-xxxg-mg59",
"https://nvd.nist.gov/vuln/detail/CVE-2026-59895",
"https://github.com/honojs/hono/commit/cd3f6f7194f0e5c9d4b26ae0cf232018d0f388fc"
],
"provider_metadata": {
"cwe_ids": [
"CWE-116",
"CWE-79"
],
"cna_assigner": "GitHub_M",
"osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/59xxx/CVE-2026-59895.json"
}
},
"related_cves": [
{
"value": "CVE-2026-59895",
"evidence": "/id"
}
],
"security_relevant": true,
"severity_evidence": "/severity/0/score"
},
"source_id": "core-osv",
"document_id": 503002,
"published_at": "2026-07-08T16:09:51.273+00:00"
}