CVE-2026-44455: Hono Web Framework XSS Vulnerability

CVE-2026-44455 Overview

CVE-2026-44455 is an HTML injection vulnerability in Hono, a web application framework supporting multiple JavaScript runtimes. The flaw resides in the hono/jsx module, where JSX element tag names are inserted into rendered HTML without validation. When developers pass untrusted input as a tag name through the programmatic jsx() or createElement() APIs during server-side rendering, attackers can break out of the intended element context and inject arbitrary HTML. The issue is tracked under [CWE-74] (Improper Neutralization of Special Elements in Output). Hono version 4.12.16 fixes the vulnerability.

Critical Impact

Attackers can inject unintended HTML into server-rendered pages when user-controlled input reaches a JSX tag name argument, enabling cross-site scripting in vulnerable applications.

Affected Products

• Hono framework versions prior to 4.12.16
• Applications using hono/jsx server-side rendering
• Node.js deployments invoking jsx() or createElement() with untrusted tag names

Discovery Timeline

• 2026-05-13 - CVE-2026-44455 published to NVD
• 2026-05-13 - Last updated in NVD database

Technical Details for CVE-2026-44455

Vulnerability Analysis

The vulnerability stems from hono/jsx writing element tag names directly into HTML output without sanitization or validation. JSX runtimes typically expect tag names to be static identifiers controlled by the developer. Hono's programmatic APIs jsx() and createElement() accept the tag name as a string argument, which some applications populate from request data such as query parameters or JSON fields.

During server-side rendering, the framework constructs the opening and closing tags by concatenating the supplied string into the HTML stream. A crafted value containing characters such as >, attribute delimiters, or additional element syntax escapes the intended tag context. The attacker then introduces arbitrary attributes, sibling elements, or script-bearing constructs.

The weakness aligns with [CWE-74] because the framework fails to neutralize special characters before placing user data into a downstream interpreter, in this case the browser HTML parser. Exploitation requires user interaction, since the malicious payload must render in a victim's browser session.

Root Cause

The root cause is missing input validation on the tag parameter inside the JSX rendering path. Hono treated tag names as trusted developer-supplied identifiers and skipped the escaping logic applied to attribute values and text content.

Attack Vector

The attack vector is network-based and requires user interaction. An attacker submits a payload to an endpoint that forwards untrusted input to jsx() or createElement() as the element type. When the response renders in a victim browser, the injected HTML executes within the application's origin, enabling script execution, content spoofing, or session-related abuse. The vulnerability description does not include published exploitation code, and the scoring vector indicates a scope change consistent with cross-site scripting impact.

Detection Methods for CVE-2026-44455

Indicators of Compromise

• Server access logs containing request parameters with HTML metacharacters such as <, >, ", or / reaching endpoints that render JSX
• Outbound responses containing unexpected <script>, <iframe>, or event-handler attributes in server-rendered HTML
• Application error logs referencing malformed tag names passed to jsx() or createElement()

Detection Strategies

• Perform static analysis of application source code to locate calls to jsx() and createElement() where the first argument is not a string literal
• Review dependency manifests (package.json, package-lock.json, yarn.lock) for hono versions below 4.12.16
• Deploy runtime web application firewall rules that flag HTML metacharacters in parameters mapped to template tag inputs

Monitoring Recommendations

• Monitor Hono application logs for rendering exceptions or anomalous tag name values during request processing
• Track Content Security Policy violation reports for inline script execution originating from server-rendered pages
• Alert on dependency drift when production builds resolve hono to a version earlier than 4.12.16

How to Mitigate CVE-2026-44455

Immediate Actions Required

• Upgrade Hono to version 4.12.16 or later across all environments using npm install hono@^4.12.16 or the equivalent package manager command
• Audit source code for any path where user input flows into the tag argument of jsx() or createElement() and replace dynamic tag names with an allowlist
• Redeploy server-side rendered applications after dependency updates and invalidate cached HTML responses

Patch Information

The maintainers released the fix in Hono 4.12.16. Details are available in the GitHub Security Advisory GHSA-69xw-7hcm-h432. The patch validates tag names before they are written to the HTML output stream.

Workarounds

• Replace dynamic tag arguments with a fixed allowlist of permitted element names such as div, span, or p
• Sanitize incoming parameters with a strict regular expression like ^[a-zA-Z][a-zA-Z0-9-]*$ before passing them to JSX APIs
• Enforce a strict Content Security Policy that blocks inline scripts to reduce the impact of injected HTML

# Configuration example
npm install hono@^4.12.16
npm ls hono