CVE-2026-59895: CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting') in honojs hono
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.
AI Analysis
Technical Summary
CVE-2026-59895 is a cross-site scripting vulnerability in the hono JavaScript framework affecting versions from 4.0.0 before 4.12.27. The cx() function in hono/css composes class names from plain strings but incorrectly marks the result as escaped without performing HTML escaping on the input. This improper neutralization of input allows untrusted className values used in JSX class attributes during server-side rendering to break out of the attribute context and inject arbitrary markup, leading to potential XSS attacks. The issue is resolved in version 4.12.27.
Potential Impact
An attacker can supply crafted className values that bypass escaping protections during server-side rendering, enabling injection of arbitrary HTML or script code. This can lead to cross-site scripting attacks that compromise confidentiality and integrity of user interactions. The CVSS score of 6.1 reflects a medium severity with network attack vector, low attack complexity, no privileges required, user interaction required, and impact on confidentiality and integrity but not availability.
Mitigation Recommendations
A fix is available in hono version 4.12.27. Users should upgrade to version 4.12.27 or later to remediate this vulnerability. No other official remediation or temporary fixes are documented. Until upgrading, avoid using untrusted input in className attributes or apply manual HTML escaping as a temporary mitigation.
CVE-2026-59895: CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting') in honojs hono
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.
CVSS v3.1
Score 6.1medium
Affected software
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AI-Powered Analysis
Machine-generated threat intelligence
Technical Analysis
CVE-2026-59895 is a cross-site scripting vulnerability in the hono JavaScript framework affecting versions from 4.0.0 before 4.12.27. The cx() function in hono/css composes class names from plain strings but incorrectly marks the result as escaped without performing HTML escaping on the input. This improper neutralization of input allows untrusted className values used in JSX class attributes during server-side rendering to break out of the attribute context and inject arbitrary markup, leading to potential XSS attacks. The issue is resolved in version 4.12.27.
Potential Impact
An attacker can supply crafted className values that bypass escaping protections during server-side rendering, enabling injection of arbitrary HTML or script code. This can lead to cross-site scripting attacks that compromise confidentiality and integrity of user interactions. The CVSS score of 6.1 reflects a medium severity with network attack vector, low attack complexity, no privileges required, user interaction required, and impact on confidentiality and integrity but not availability.
Mitigation Recommendations
A fix is available in hono version 4.12.27. Users should upgrade to version 4.12.27 or later to remediate this vulnerability. No other official remediation or temporary fixes are documented. Until upgrading, avoid using untrusted input in className attributes or apply manual HTML escaping as a temporary mitigation.
Technical Details
- Data Version
- 5.2
- Assigner Short Name
- GitHub_M
- Date Reserved
- 2026-07-07T16:40:07.983Z
- Cvss Version
- 3.1
- State
- PUBLISHED
- Remediation Level
- null
Threat ID: 6a4e7ad4c9d9e3dbe36a7d72
Added to database: 07/08/2026, 16:29:08 UTC
Last enriched: 07/08/2026, 16:44:11 UTC
Last updated: 07/08/2026, 23:15:06 UTC
Views: 6
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