Vulnerability · Published Jul 8, 2026 · Assigned by GitHub_M

CVE-2026-59895Hono: Server-Side XSS via JSX Escaping Bypass in cx() Utility

Medium 6.1

In plain English

A medium-severity cross-site scripting in hono from honojs. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.3% (higher than 26% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.

Severity (CVSS 3.1)6.1Medium

Exploit odds (30 days)0.3%top 74.1% of all CVEs

Exploited in the wildNo reportsCISA SSVC: none

Attack toolingNoneno public tooling known

Official 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.

Affected packages & fixed versions

Ecosystem	Package	Fixed in	Advisory
npm	hono	4.12.27	GHSA-w62v-xxxg-mg59

Affected products (as reported)

Vendor	Product	Versions
honojs	hono	>= 4.0.0, < 4.12.27

Weakness: CWE-79, CWE-116 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N

References

https://github.com/honojs/hono/security/advisories/GHSA-w62v-xxxg-mg59 x_refsource_CONFIRM
https://github.com/honojs/hono/commit/cd3f6f7194f0e5c9d4b26ae0cf232018d0f388fc x_refsource_MISC
https://github.com/honojs/hono/releases/tag/v4.12.27 x_refsource_MISC