What’s Vulnerable › Vulnerabilities

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

• Severity: medium (CVSS 6.1 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.3% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-07-08 · updated 2026-10-25
• Weakness: CWE-79

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 products

• honojs hono: from 4.0.0 before 4.12.27 — fixed in 4.12.27

How to fix

Upgrade to a fixed version: honojs hono 4.12.27. Check the vendor advisory for mitigations.

References

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

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