CVE-2026-24771: Hono Web Framework XSS Vulnerability

CVE-2026-24771 Overview

A Cross-Site Scripting (XSS) vulnerability exists in the ErrorBoundary component of the hono/jsx library within the Hono Web application framework. Hono is a lightweight Web application framework designed to provide support for any JavaScript runtime environment. Prior to version 4.11.7, certain usage patterns of the ErrorBoundary component allow untrusted user-controlled strings to be rendered as raw HTML, enabling arbitrary script execution in the victim's browser.

Critical Impact

Attackers can execute arbitrary JavaScript code in the context of a victim's browser session, potentially leading to session hijacking, credential theft, defacement, or further attacks against users of affected applications.

Affected Products

• Hono framework versions prior to 4.11.7
• Applications using the hono/jsx ErrorBoundary component
• Any JavaScript runtime environment running vulnerable Hono versions

Discovery Timeline

• 2026-01-27 - CVE CVE-2026-24771 published to NVD
• 2026-01-29 - Last updated in NVD database

Technical Details for CVE-2026-24771

Vulnerability Analysis

This vulnerability is classified as CWE-79 (Improper Neutralization of Input During Web Page Generation), commonly known as Cross-Site Scripting (XSS). The flaw resides in the ErrorBoundary component of Hono's JSX library, which is designed to catch and handle errors in component rendering.

Under specific usage patterns, the ErrorBoundary component fails to properly sanitize or escape user-controlled input before rendering it as HTML. When error messages or related data contain user-supplied content, malicious HTML and JavaScript can be injected and executed within the victim's browser context.

The attack requires user interaction since a victim must visit a page where the malicious payload is rendered through the vulnerable ErrorBoundary component. The changed scope characteristic means successful exploitation can impact resources beyond the vulnerable component's security context.

Root Cause

The root cause of this vulnerability lies in insufficient output encoding within the ErrorBoundary component. When handling and displaying error information, the component renders certain strings directly as HTML without proper escaping. This allows specially crafted input containing HTML tags and JavaScript to bypass normal text rendering and execute as active content in the browser.

Attack Vector

The attack vector is network-based, requiring an attacker to craft malicious input that flows through the application and triggers the vulnerable code path in the ErrorBoundary component. Successful exploitation requires:

1. An application using the vulnerable version of Hono with the hono/jsx ErrorBoundary component
2. User-controlled data that reaches the ErrorBoundary component's rendering logic
3. User interaction where the victim visits or interacts with the affected page

The vulnerability allows attackers to inject malicious scripts that execute with the same privileges as the legitimate application, enabling actions such as stealing session tokens, capturing user input, redirecting users to malicious sites, or performing actions on behalf of the authenticated user.

For detailed technical information about the vulnerability mechanism and the specific code paths involved, refer to the GitHub Security Advisory GHSA-9r54-q6cx-xmh5.

Detection Methods for CVE-2026-24771

Indicators of Compromise

• Unexpected or malformed HTML/JavaScript appearing in error handling output
• User reports of suspicious pop-ups or redirects when errors occur in the application
• Web application firewall logs showing XSS payload attempts targeting error handlers
• Browser console errors indicating blocked inline scripts (if CSP is enabled)

Detection Strategies

• Audit application dependencies to identify Hono versions prior to 4.11.7
• Review code for usage of the ErrorBoundary component from hono/jsx with user-controlled data
• Implement Web Application Firewall (WAF) rules to detect common XSS payloads in request parameters
• Enable Content Security Policy (CSP) headers to detect and block unauthorized inline script execution

Monitoring Recommendations

• Monitor web server logs for requests containing common XSS patterns such as <script>, onerror=, javascript:, and similar injection attempts
• Implement client-side error logging to capture any unexpected script execution behavior
• Set up alerts for CSP violation reports that may indicate attempted or successful XSS exploitation
• Track dependency versions across development environments to ensure timely patching

How to Mitigate CVE-2026-24771

Immediate Actions Required

• Upgrade Hono framework to version 4.11.7 or later immediately
• Audit existing applications for usage of the ErrorBoundary component with user-supplied data
• Implement Content Security Policy (CSP) headers to provide defense-in-depth against XSS attacks
• Review and enhance input validation and output encoding practices throughout the application

Patch Information

The vulnerability has been addressed in Hono version 4.11.7. The fix ensures proper sanitization of content rendered by the ErrorBoundary component, preventing user-controlled strings from being interpreted as raw HTML.

The patch commit can be reviewed at the GitHub Commit Update. Organizations should update their package dependencies to incorporate this security fix.

Workarounds

• Implement strict Content Security Policy (CSP) headers that disallow inline scripts and restrict script sources
• Avoid passing user-controlled data directly to the ErrorBoundary component until the patch is applied
• Manually sanitize any user input that may be rendered in error handling contexts using a trusted HTML sanitization library
• Consider implementing a custom error boundary with explicit output encoding if immediate upgrade is not possible

# Update Hono to patched version
npm update hono@4.11.7

# Or specify minimum version in package.json
# "hono": ">=4.11.7"

# Verify installed version
npm list hono