# CVE-2026-59895: Hono: Server-Side XSS via JSX Escaping Bypass in cx() Utility

> Attackers can inject arbitrary markup via unescaped class names in server-side rendered JSX, potentially leading to code execution.

- **Severity:** Medium 6.1 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/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:** 8 Jul 2026
- **Updated:** 8 Jul 2026
- **Also known as:** CLEANSTART-2026-HY09448, ECHO-7335-a8b9-129c, GHSA-w62v-xxxg-mg59, MINI-2pm7-mg2c-24v7, MINI-3c5c-hwqx-wpfg, MINI-58c9-6263-wgxq, MINI-c7r8-jwpm-8fcg, MINI-fvfg-7x9c-frv6, MINI-jg4g-pq4q-rj42, MINI-mgq2-hvh5-9v4q, MINI-r9x3-hvgj-xqfx, MINI-rwwp-h8jq-g6hf, MINI-w5gx-j99x-p66h, MINI-w8px-xmj7-ph2h, ROOT-APP-NPM-CVE-2026-59895

## What is CVE-2026-59895?

CVE-2026-59895 is a medium-severity cross-site scripting vulnerability in honojs hono, published on 8 Jul 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. 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.

Weakness: CWE-79 (Improper Neutralization of Input During Web Page Generation), CWE-116 (Improper Encoding or Escaping of Output)

## Which versions are affected by CVE-2026-59895?

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


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `hono` | npm | From 4.0.0 | 4.12.27 |
| `hono` | npm | From 4.0.0 | 4.12.27 |

Products: Hono Hono.

## How do I fix CVE-2026-59895?

Upgrade hono to 4.12.27 or later.

## Is CVE-2026-59895 being exploited?

There is no known exploitation of CVE-2026-59895 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-2026-59895 and fix it if it is affected.

What it is: CVE-2026-59895 is a medium-severity cross-site scripting vulnerability in honojs hono, published on 8 Jul 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-2026-59895 in the wild and no public exploit code.

Affected packages and fixed versions:
- hono (npm): affected from 4.0.0; fixed in 4.12.27
- hono (npm): affected from 4.0.0; fixed in 4.12.27

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-2026-59895/ (Markdown: https://insights.sbomify.com/CVE-2026-59895/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-59895
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-59895
- OSV: https://osv.dev/vulnerability/CVE-2026-59895

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-59895/
Summaries are generated and may contain mistakes; the official description above is the record.