{"id":"GHSA-w62v-xxxg-mg59","summary":"Hono: Server-Side XSS via JSX Escaping Bypass in cx() Utility","details":"### Summary\n\n`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).\n\n### Details\n\nBecause 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`.\n\n### Impact\n\nDuring 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.\n\nThis may lead to:\n\n- Execution of attacker-controlled script in the victim's browser session.\n- Session hijacking, credential theft, or actions performed on behalf of the victim.\n\nApplications are affected only if they render JSX server-side and pass untrusted input as a class name to `cx()`.","aliases":["CVE-2026-59895"],"modified":"2026-07-21T18:45:58.638931549Z","published":"2026-07-21T18:33:50Z","database_specific":{"github_reviewed_at":"2026-07-21T18:33:50Z","nvd_published_at":"2026-07-08T17:17:27Z","cwe_ids":["CWE-116","CWE-79"],"severity":"MODERATE","github_reviewed":true},"references":[{"type":"WEB","url":"https://github.com/honojs/hono/security/advisories/GHSA-w62v-xxxg-mg59"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-59895"},{"type":"WEB","url":"https://github.com/honojs/hono/commit/cd3f6f7194f0e5c9d4b26ae0cf232018d0f388fc"},{"type":"PACKAGE","url":"https://github.com/honojs/hono"},{"type":"WEB","url":"https://github.com/honojs/hono/releases/tag/v4.12.27"}],"affected":[{"package":{"name":"hono","ecosystem":"npm","purl":"pkg:npm/hono"},"ranges":[{"type":"SEMVER","events":[{"introduced":"4.0.0"},{"fixed":"4.12.27"}]}],"database_specific":{"source":"https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2026/07/GHSA-w62v-xxxg-mg59/GHSA-w62v-xxxg-mg59.json"}}],"schema_version":"1.9.0","severity":[{"type":"CVSS_V3","score":"CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N"}]}