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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. 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Complete affected data, logical configurations and SSVC are retained in the original JSON."},"key":"nvd:CVE-2026-59895","identifiers":["CVE-2026-59895"]},"retained":false,"historicalAffected":[]},{"revision":"7a0fb76e19824ae589c9f41708699a6b","observedAt":"2026-10-24T13:17:17.793+00:00","statement":{"source":"osv","id":"GHSA-w62v-xxxg-mg59","aliases":["CVE-2026-59895"],"title":"Hono: Server-Side XSS via JSX Escaping Bypass in cx() Utility","description":"### 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()`.","state":0,"publishedAt":"2026-07-21T18:33:50+00:00","modifiedAt":"2026-09-10T03:51:12.3715078+00:00","affected":[{"ecosystem":"npm","name":"hono","ranges":[{"type":"SEMVER","events":[{"kind":"introduced","version":"4.0.0"},{"kind":"fixed","version":"4.12.27"}]}],"versions":[],"rawVersionEvidence":null}],"metrics":[{"system":"CVSS_V3","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N","score":null,"severity":null},{"system":"Publisher rating","vector":null,"score":null,"severity":"MODERATE"}],"references":["https://github.com/honojs/hono/security/advisories/GHSA-w62v-xxxg-mg59","https://nvd.nist.gov/vuln/detail/CVE-2026-59895","https://github.com/honojs/hono/commit/cd3f6f7194f0e5c9d4b26ae0cf232018d0f388fc","https://github.com/honojs/hono","https://github.com/honojs/hono/releases/tag/v4.12.27"],"sourceUrl":"https://github.com/advisories/GHSA-w62v-xxxg-mg59","license":"GitHub Advisory Database · CC-BY-4.0","key":"osv:GHSA-w62v-xxxg-mg59","identifiers":["GHSA-w62v-xxxg-mg59","CVE-2026-59895"]},"retained":false,"historicalAffected":[]}],"coverage":[{"source":"cisa-kev:global","scope":"Complete CISA KEV catalog; all vendors. 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