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

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

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

EPSS

• CVE-2026-44458: 0.20% estimated exploitation activity in the next 30 days; percentile 9.53 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Summary 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. Details style object values are serialized into a CSS declaration list and escaped for HTML attribute context only. Characters that act as CSS declaration boundaries — such as ;, comment markers, quoted strings, and block delimiters — are valid in HTML attribute content and can extend a value beyond its assigned property. This issue arises when untrusted input is interpolated into a JSX style object and rendered server-side. Impact An attacker who can control the value or property name of a style object may inject arbitrary CSS declarations. This may lead to: - Visual manipulation of the page, including full-viewport overlays usable for phishing - Outbound…

Published by the source

9 May 2026, 00:46 UTC

Last modified by the source

10 Sep 2026, 03:50 UTC

Source last checked

26 Oct 2026, 12:51 UTC

1. Revision 2 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-qp7p-654g-cw7p

2. Revision 1 · created · 24 Oct 2026

   Published from osv record GHSA-qp7p-654g-cw7p

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# Patch Next advisory brief: CVE-2026-44458

Advisory: Hono has CSS Declaration Injection via Style Object Values in JSX SSR
IDs: CVE-2026-44458, GHSA-qp7p-654g-cw7p
Record: https://patchnext.com/advisories/cve-2026-44458 (revision 2, source checked 26 Oct 2026, 12:51 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 4.3)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: hono 4.12.18. A vendor fix does not mean a deployment is fixed.

## Affected components
- npm hono: affected < 4.12.18; fixed in 4.12.18

## Suggested inspection (read-only)
- `npm ls hono --all`: lists every installed copy and version, including transitive ones. Run in the project root after `npm ci`.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on hono.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://osv.dev/vulnerability/GHSA-qp7p-654g-cw7p (OSV record GHSA-qp7p-654g-cw7p lists affected ranges: npm hono >=0 <4.12.18 (fixed))
- Verified: https://github.com/advisories/GHSA-qp7p-654g-cw7p (GitHub-reviewed advisory GHSA-qp7p-654g-cw7p lists affected ranges: npm hono >=0 <4.12.18)

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