Withdrawn by the publisher.

Affected: CleanStart: langfuse

Package langfuse version 3.213.0-r1 fixes 24 vulnerabilities: CVE-2026-59895, CVE-2026-59896, CVE-2026-59897, CVE-2026-69207, CVE-2026-71848...

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.

Affected: npm: hono

### Summary

`cx()` in `hono/css` composes class names from plain strings but marks the result as already-escaped without HTML-escaping the input. When the result is used as a JSX `class` attribute during server-side rendering, the value is written into the attribute unescaped, so untrusted input can break out of the `class` attribute and inject arbitrary markup, leading to Cross-Site Scripting (XSS).

### Details

Because the composed value is treated as pre-escaped, the HTML attribute escaping normally applied to interpolated values is skipped, and characters such as `"` pass through unescaped — allowing a value to terminate the attribute and add further attributes or elements. This arises when an application passes untrusted, user-controlled input as a class name to `cx()`, for example when merging a base class with an externally provided `className`.

### Impact

During server-side rendering, an attacker who controls a value passed to `cx()` can inject arbitrary HTML into the page, resulting in stored or reflected XSS in the victim's browser.

This may lead to:

- Execution of attacker-controlled script in the victim's browser session. - Session hijacking, credential theft, or actions performed on behalf of the victim.

Applications are affected only if they render JSX server-side and pass untrusted input as a class name to `cx()`.