Medium severity · published Jul 8, 2026
CVE-2026-59895
Hono: Server-Side XSS via JSX Escaping Bypass in cx() Utility
6.1
CVSS
0.3%
EPSS
No
On KEV
Description
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.
CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
Required
Confidentiality
Low
Integrity
Low
Availability
None
Scope
Changed
Exploitation
Is it being used?
Exploit prediction (EPSS)0.3% · higher than 26% of CVEs
Exploited in the wildNo evidence yet
CISA KEVNot listed
Ransomware campaign useNot known
Affected products
Which versions
HO
hono · honojs
>= 4.0.0, < 4.12.27 · source: vendor, NVD
References
NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-59895
CVE.org
https://www.cve.org/CVERecord?id=CVE-2026-59895
Patch
https://github.com/honojs/hono/commit/cd3f6f7194f0e5c9d4b26ae0cf232018d0f388fc
Release Notes
https://github.com/honojs/hono/releases/tag/v4.12.27
Vendor Advisory
https://github.com/honojs/hono/security/advisories/GHSA-w62v-xxxg-mg59
More from hono
9.8
CVE-2026-29045
Hono: Arbitrary file access via serveStatic vulnerability
8.1
CVE-2025-62610
Hono Improperly Authorizes JWT Audience Validation
7.5
CVE-2026-39408
Hono has a path traversal in toSSG() allows writing files outside the output directory
7.5
CVE-2026-27700
Hono is Vulnerable to Authentication Bypass by IP Spoofing in AWS Lambda ALB conninfo
7.5
CVE-2025-58362
Hono contains a flaw in URL path parsing, potentially leading to path confusion