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

Quick assessment

Affected
honojs hono
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

Hono是Hono团队开源的一个用 TypeScript 编写的 Web 框架。 Hono 4.0.0版本至4.12.27之前版本存在安全漏洞，该漏洞源于hono/css中的cx()函数将纯字符串组合为class名，但未对输入进行HTML转义即标记为已转义，允许在服务器端渲染期间使用不可信的className值，从而突破属性并注入任意标记。

CVSS 6.1 · Medium EPSS 0.33% · P23

Affected Version Matrix 1

VendorProduct Version RangeStatus
honojs hono >= 4.0.0, < 4.12.27 affected
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I. Basic Information for CVE-2026-59895

Vulnerability Information
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Vulnerability Title
Hono: Server-Side XSS via JSX Escaping Bypass in cx() Utility
Source: CVE Program / CVE List V5
Vulnerability 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.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
Source: CVE Program / CVE List V5
Vulnerability Type
在Web页面生成时对输入的转义处理不恰当(跨站脚本)
Source: CVE Program / CVE List V5
Vulnerability Title
Hono 输出处理不当漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
Hono是Hono团队开源的一个用 TypeScript 编写的 Web 框架。 Hono 4.0.0版本至4.12.27之前版本存在安全漏洞，该漏洞源于hono/css中的cx()函数将纯字符串组合为class名，但未对输入进行HTML转义即标记为已转义，允许在服务器端渲染期间使用不可信的className值，从而突破属性并注入任意标记。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)

Affected Products

Vendor Product Affected Versions CPE Subscribe
honojs hono >= 4.0.0, < 4.12.27 -

II. Public POCs for CVE-2026-59895

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III. Intelligence Information for CVE-2026-59895

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Patches & Fixes for CVE-2026-59895 (1)

Vendor Advisories for CVE-2026-59895 (1)

Vendor Pages for CVE-2026-59895 (1)

Same Patch Batch · honojs · 2026-07-08 · 3 CVEs total

CVE-2026-59896 6.5 MEDIUM hono/jsx does not isolate context per request, leading to cross-request data disclosure
CVE-2026-59897 4.8 MEDIUM Hono: API Gateway v1 adapter can drop a distinct repeated request header value during de-d

IV. Related Vulnerabilities

Same product: hono
Same vendor: honojs
Same weakness: CWE-79

V. Comments for CVE-2026-59895

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