# CVE-2026-44458: Hono: CSS Declaration Injection via Style Object Values in JSX SSR

> Attackers can inject CSS declarations via style objects in Hono JSX SSR, potentially altering page appearance or enabling UI redressing attacks.

- **Severity:** Medium 4.3 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:L/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** A user has to click or open something
- **Fix available:** Yes
- **Published:** 13 May 2026
- **Updated:** 14 May 2026
- **Also known as:** CLEANSTART-2026-EO52951, CLEANSTART-2026-EQ24624, ECHO-63bb-4218-a72e, GHSA-qp7p-654g-cw7p, MINI-5jrh-xjj6-q9mr, MINI-68wm-fm8q-f8wg, MINI-743v-37p9-j24w, MINI-8mpg-m38c-79m6, MINI-926w-xc7v-h43c, MINI-f9f6-4rxf-mfcj, MINI-ggxc-7rqx-q73f, MINI-pjxw-r4vh-qqcc, MINI-qxpr-jmw9-6wvf, ROOT-APP-NPM-CVE-2026-44458

## What is CVE-2026-44458?

CVE-2026-44458 is a medium-severity cross-site scripting vulnerability in honojs hono, published on 13 May 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.

### Official description

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.

Weakness: CWE-74 (Improper Neutralization of Special Elements in Output Used by a Downstream Component), CWE-116 (Improper Encoding or Escaping of Output)

## Which versions are affected by CVE-2026-44458?

2 open source packages ship an affected version, including hono. It affects 1 product.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `hono` | npm | All versions | 4.12.18 |
| `hono` | npm | All versions | 4.12.18 |

Products: Hono Hono.

## How do I fix CVE-2026-44458?

Upgrade hono to 4.12.18 or later.

## Is CVE-2026-44458 being exploited?

There is no known exploitation of CVE-2026-44458 in the wild and no public exploit code.

## Other vulnerabilities in honojs hono

- [CVE-2026-27700](https://insights.sbomify.com/CVE-2026-27700/): Hono is Vulnerable to Authentication Bypass by IP Spoofing in AWS Lambda ALB conninfo (high 8.2)
- [CVE-2026-22817](https://insights.sbomify.com/CVE-2026-22817/): JWT Algorithm Confusion via Unsafe Default (HS256) in Hono JWT Middleware Allows Token Forgery and Auth Bypass (high 8.2)
- [CVE-2026-22818](https://insights.sbomify.com/CVE-2026-22818/): JWT algorithm confusion in Hono JWK Auth Middleware when JWK lacks "alg" (untrusted header.alg fallback) (high 8.2)
- [CVE-2025-62610](https://insights.sbomify.com/CVE-2025-62610/): Hono Improperly Authorizes JWT Audience Validation (high 8.1)
- [CVE-2026-29045](https://insights.sbomify.com/CVE-2026-29045/): Hono: Arbitrary file access via serveStatic vulnerability (high 7.5)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-44458 and fix it if it is affected.

What it is: CVE-2026-44458 is a medium-severity cross-site scripting vulnerability in honojs hono, published on 13 May 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.
Exploitation: There is no known exploitation of CVE-2026-44458 in the wild and no public exploit code.

Affected packages and fixed versions:
- hono (npm): affected all versions; fixed in 4.12.18
- hono (npm): affected all versions; fixed in 4.12.18

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-44458/ (Markdown: https://insights.sbomify.com/CVE-2026-44458/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-44458
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-44458
- OSV: https://osv.dev/vulnerability/CVE-2026-44458

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-44458/
Summaries are generated and may contain mistakes; the official description above is the record.