CVE-2026-24771 identifies a Cross-Site Scripting (XSS) vulnerability in the honojs web application framework, specifically within the ErrorBoundary component of the hono/jsx library versions prior to 4.11.7. Hono is a versatile JavaScript framework supporting multiple runtimes, commonly used for building web applications. The vulnerability arises because under certain usage patterns, untrusted user-controlled strings are rendered directly as raw HTML without proper neutralization or sanitization. This improper input handling violates CWE-79 standards and allows attackers to inject malicious scripts that execute in the context of the victim's browser session. Exploitation requires user interaction, such as clicking a crafted link or visiting a malicious page that triggers the vulnerable error rendering. The CVSS 3.1 base score is 4.7 (medium), reflecting network attack vector, high attack complexity, no privileges required, and user interaction needed. The impact includes potential confidentiality and integrity loss through script execution, such as session token theft or manipulation of page content. The vulnerability has been patched in hono version 4.11.7, which properly sanitizes or escapes user input in the ErrorBoundary component to prevent raw HTML injection. No known exploits have been reported in the wild as of the publication date. Organizations using affected versions should upgrade promptly and audit their use of error handling components to ensure no unsafe rendering occurs.

For European organizations, this vulnerability poses a risk primarily to web applications built using the hono framework versions prior to 4.11.7. Successful exploitation could lead to client-side script execution, enabling attackers to steal session cookies, perform actions on behalf of users, or deface web content. This can result in loss of user trust, data breaches, and regulatory non-compliance under GDPR due to compromised user data confidentiality. The medium severity score reflects that exploitation requires user interaction and has high complexity, limiting widespread automated attacks. However, targeted attacks against high-value applications or services remain a concern. Organizations in sectors such as finance, e-commerce, and public services that rely on hono-based web applications are particularly vulnerable. The impact on availability is minimal, but integrity and confidentiality risks are notable. Given the increasing use of JavaScript frameworks in Europe, the vulnerability could affect a broad range of applications if not addressed.

1. Upgrade all hono framework instances to version 4.11.7 or later immediately to apply the official patch that neutralizes the XSS vulnerability in the ErrorBoundary component. 2. Conduct a thorough code review of all custom error handling and rendering logic to ensure that no user-controlled input is rendered as raw HTML without proper sanitization or escaping. 3. Implement Content Security Policy (CSP) headers to restrict the execution of unauthorized scripts and reduce the impact of potential XSS attacks. 4. Employ automated security testing tools that can detect XSS vulnerabilities in development and staging environments, focusing on error boundary and JSX rendering components. 5. Educate developers on secure coding practices related to input validation and output encoding, especially in error handling contexts. 6. Monitor web application logs and user reports for suspicious activity that might indicate attempted exploitation. 7. If upgrading immediately is not feasible, apply temporary mitigations such as disabling or restricting the use of the vulnerable ErrorBoundary component or sanitizing inputs before they reach it.