CVE-2026-59895: hono XSS — Fix

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.

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CVSS v3.1 Score

6.1

MEDIUM

CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N

EPSS — Exploit Prediction

0.0019

Probability of exploitation

0.09%

Percentile rank

EPSS estimates the probability that this vulnerability will be exploited in the wild within the next 30 days. A higher score means more likely to be exploited.

Weakness Type (CWE)

CWE-79 Cross-site Scripting (XSS)

CWE-116 CWE-116

Affected Products

Vendor	Product	Versions
hono	hono	4.0.0 — 4.12.27

References

Advisories & Patches

https://github.com/honojs/hono/commit/cd3f6f7194f0e5c9d4b26ae0cf232018d0f388fc https://github.com/honojs/hono/security/advisories/GHSA-w62v-xxxg-mg59

Other References

https://github.com/honojs/hono/releases/tag/v4.12.27

Frequently Asked Questions

What is CVE-2026-59895? +

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. It has a CVSS v3.1 base score of 6.1 (MEDIUM).

How severe is CVE-2026-59895? +

CVE-2026-59895 has a CVSS v3.1 score of 6.1 out of 10, rated MEDIUM. This is a medium-severity vulnerability that should be remediated as part of regular maintenance. The EPSS score is 0.0019, placing it in the 0th percentile for exploitation probability.

What products are affected by CVE-2026-59895? +

CVE-2026-59895 affects products from hono, specifically: hono. Check the affected products table above for specific version ranges.

How do I check if I'm vulnerable to CVE-2026-59895? +

You can use Secably's free Website Scanner to check your website for known vulnerabilities. For infrastructure scanning, use the Port Scanner to identify exposed services that may be affected. Check the vendor advisories linked above for specific patch and version information.

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