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.
- 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
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.
Which versions are affected by CVE-2026-59895?
2 open source packages ship an affected version, including hono. It affects 1 product.
| Package | Affected | Fixed in |
|---|---|---|
hono npm | From 4.0.0 | 4.12.27 |
hono npm | From 4.0.0 | 4.12.27 |
Products include Hono Hono.
How do I fix CVE-2026-59895?
Upgrade hono to 4.12.27 or later.
Escape output for the context it lands in and set a strict Content Security Policy. Upgrading the affected component is the real fix. More about Cross-site scripting.
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 Hono is Vulnerable to Authentication Bypass by IP Spoofing in AWS Lambda ALB conninfo
- CVE-2026-22817 JWT Algorithm Confusion via Unsafe Default (HS256) in Hono JWT Middleware Allows Token Forgery and Auth Bypass
- CVE-2026-22818 JWT algorithm confusion in Hono JWK Auth Middleware when JWK lacks "alg" (untrusted header.alg fallback)
- CVE-2025-62610 Hono Improperly Authorizes JWT Audience Validation
- CVE-2026-29045 Hono: Arbitrary file access via serveStatic vulnerability
Sources
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 and 9 more.