# CVE-2026-126359: Hono: `css` helper does not escape a closing tag split between the template and an interpolated value, allowing HTML injection

Status: published. Published: 2026-11-12. Updated: 2026-11-12.

Hono is a Web application framework that provides support for any JavaScript runtime. From 3.12.0 until 4.13.16, the css helper in hono/css escapes interpolated string values separately and therefore fails to neutralize a closing style tag when < ends the template text or a preceding value and / begins the next attacker-controlled value. During server-side rendering, the combined output can close the <Style /> element early and cause the remainder of the interpolated value to be interpreted as HTML. Applications that place an untrusted string immediately after < in a css template, including adjacent untrusted interpolations, can expose viewers to attacker-controlled HTML or script and information accessible to that page. Other uses of the css helper are not affected. This issue is fixed in version 4.13.16.

## Remediation

No remediation reported in collected sources

## Affected products and versions

- honojs / hono: >= 3.12.0, < 4.13.16 (affected). Source: CNA: GitHub_M

## Severity and prioritization

- CVSS 3.1: 3.4 (low); CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:C/C:L/I:N/A:N; source: CNA: GitHub_M

- CISA KEV: No listing in collected sources

- EPSS: Not available

- SSVC: Not available

- Weaknesses: CWE-79

## Exploit evidence

No exploit evidence in collected sources. This is not proof of no exploitation.

## References

- https://github.com/honojs/hono/security/advisories/GHSA-3gg2-335m-rxc6 (CNA: GitHub_M; x_refsource_CONFIRM)

- https://github.com/honojs/hono/commit/15bbd96ad1b62a0b189db4fd8dc7bf8ef280c513 (CNA: GitHub_M; x_refsource_MISC)

- https://github.com/honojs/hono/releases/tag/v4.13.16 (CNA: GitHub_M; x_refsource_MISC)

## Provenance

- CNA: GitHub_M: https://www.cve.org/CVERecord?id=CVE-2026-126359; retrieved 2026-11-12; source updated 2026-11-12

Revision: eedae90ba9fde8a253b7735168eeab7ecbd2296a8da25ddd6a9d007c64f707d8

Canonical: https://y2.dev/cve/CVE-2026-126359

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