Hono: CSS Declaration Injection via Style Object Values in JSX SSR

published 2026-05-09 6 mo ago modified 2026-10-26 14 d ago also GHSA-qp7p-654g-cw7p , EUVD-2026-30037

cvss: 4.3; version 3.1, CNA
cisa kev: Not listed; not in CISA's catalog
epss: 0.2%; EPSS 0.2% chance of exploitation in 30 days, percentile 9%
public exploits: 0; none known

Hono is a Web application framework that provides support for any JavaScript runtime. Prior to 4.12.18, the JSX renderer escapes style attribute object values for HTML but not for CSS. Untrusted input in a style object value or property name can therefore inject additional CSS declarations into the rendered style attribute. The impact is limited to CSS and does not allow JavaScript execution or HTML attribute breakout. This vulnerability is fixed in 4.12.18.

Patch / fix

fixed in 2

npm hono 4.12.18
hono hono 4.12.18

CISA SSVC

Exploitation: none
Automatable: no
Technical impact: partial
Assessed: 5 mo ago (2026-05-14)

Exploit prediction

0.20% chance of exploitation in the next 30 days, higher than 9% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by	version	score	vector
CNA	3.1	4.3	CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:L/A:N
GitHub	3.1	4.3	CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:L/A:N

Affected packages

ecosystem	package	affected	fixed in
npm	hono	<4.12.18	4.12.18

Affected products

honojs hono

Classification

Weakness

CWE-74 Improper Neutralization of Special Elements in Output Used by a Downstream Component
CWE-116 Improper Encoding or Escaping of Output

References

github.com /honojs/hono/security/advisories/GHSA-qp7p-654g-cw7p
web, vendor-advisory
github.com /honojs/hono
package

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.

Summary