CVE-2026-56761 Overview
CVE-2026-56761 is an HTML injection vulnerability in the Hono web framework affecting versions prior to 4.12.14. The flaw resides in the JSX server-side rendering (SSR) component, which fails to properly validate attribute names before serializing them into HTML output. Attackers can supply malformed attribute keys containing characters such as quotes or angle brackets to escape tag boundaries. This breakout allows injection of arbitrary attributes or HTML elements into the rendered response. The vulnerability is categorized under CWE-79 (Improper Neutralization of Input During Web Page Generation).
Critical Impact
Attackers can inject arbitrary HTML or attributes into server-rendered pages, enabling cross-site scripting and content manipulation in applications that pass untrusted data into JSX attribute names.
Affected Products
- Hono web framework versions before 4.12.14
- Applications using Hono JSX server-side rendering
- Server-rendered routes accepting user-controlled attribute keys
Discovery Timeline
- 2026-06-24 - CVE-2026-56761 published to NVD
- 2026-06-25 - Last updated in NVD database
Technical Details for CVE-2026-56761
Vulnerability Analysis
The Hono framework provides a JSX runtime for rendering components on the server. During rendering, the framework serializes JSX elements into HTML strings by writing tag names, attribute keys, and attribute values to an output buffer. The SSR logic sanitizes attribute values but does not apply the same neutralization to attribute names. When developers spread untrusted objects into JSX elements, attacker-controlled keys reach the serializer unfiltered.
Because attribute names are concatenated directly into the HTML tag, characters such as ", >, or < terminate the current attribute or tag context. Once the parser context breaks, the attacker can append new attributes, event handlers, or entire elements. This produces stored or reflected HTML injection depending on how the application sources its input.
Root Cause
The root cause is missing input validation on JSX attribute keys within the SSR pipeline. The serializer assumes attribute names are developer-controlled identifiers and skips HTML entity encoding for them. This assumption fails when user input flows into objects spread onto JSX elements through patterns like <div {...userInput} />.
Attack Vector
Exploitation requires a Hono application that renders JSX server-side and passes attacker-influenced data into attribute names. The attacker submits a crafted payload, for example a JSON body or query parameter, containing a key such as x" onmouseover="alert(1). When the server spreads this object onto a JSX element, the rendered HTML contains the injected handler. User interaction is required to trigger the resulting script, consistent with the CVSS UI:P metric. See the GitHub Security Advisory and the VulnCheck Advisory on Hono HTML Injection for technical details.
Detection Methods for CVE-2026-56761
Indicators of Compromise
- HTTP request bodies or query parameters containing JSON keys with ", <, >, or whitespace characters intended for attribute injection
- Server response HTML containing unexpected attributes such as onerror, onmouseover, or onload adjacent to user-influenced data
- Outbound requests from rendered pages to attacker-controlled domains following user interaction
Detection Strategies
- Review application dependency manifests for hono versions earlier than 4.12.14 using software composition analysis tooling
- Add static analysis rules that flag JSX spread expressions sourced from request input, such as <Element {...req.body} />
- Inspect rendered HTML in integration tests for malformed attribute names containing non-identifier characters
Monitoring Recommendations
- Log and alert on HTTP requests containing structured input with keys that include quote or angle-bracket characters
- Monitor web application firewall telemetry for reflected payloads matching attribute-injection patterns
- Track Content Security Policy violation reports for inline event handlers that should not appear in legitimate output
How to Mitigate CVE-2026-56761
Immediate Actions Required
- Upgrade Hono to version 4.12.14 or later across all services and deployment artifacts
- Audit application code for JSX spread patterns that propagate untrusted objects into element attributes
- Restrict attribute keys passed to JSX elements to a server-side allowlist of expected identifiers
Patch Information
The Hono maintainers fixed the issue in version 4.12.14 by neutralizing unsafe characters in attribute names during SSR. Refer to the GitHub Security Advisory GHSA-458j-xx4x-4375 for the upstream remediation details and patched commit references.
Workarounds
- Avoid spreading user-controlled objects directly into JSX elements and instead pass only validated, named props
- Validate inbound JSON keys against a strict regular expression such as ^[A-Za-z][A-Za-z0-9_-]*$ before rendering
- Deploy a Content Security Policy that blocks inline event handlers and inline scripts to limit exploitation impact
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
