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hono Improperly Handles JSX Attribute Names Allows HTML Injection in hono/jsx SSR

Moderate severity GitHub Reviewed Published Apr 15, 2026 in honojs/hono • Updated Apr 16, 2026

Package

npm hono (npm)

Affected versions

< 4.12.14

Patched versions

4.12.14

Description

Summary

Improper handling of JSX attribute names in hono/jsx allows malformed attribute keys to corrupt the generated HTML output.

When untrusted input is used as attribute keys during server-side rendering, specially crafted keys can break out of attribute or tag boundaries and inject unintended HTML.

Details

When rendering JSX elements to HTML strings, attribute values are escaped, but attribute names (keys) were previously inserted into the output without validation.

If an attribute name contains characters such as ", >, or whitespace, it can alter the structure of the generated HTML.

For example, malformed attribute names can:

  • Break out of the current attribute and introduce unintended additional attributes
  • Break out of the current HTML tag and inject new elements into the output

This issue arises when untrusted input (such as query parameters or form data) is used as JSX attribute keys during server-side rendering.

Impact

An attacker who can control attribute keys used in JSX rendering may inject unintended attributes or HTML elements into the generated output.

This may lead to:

  • Injection of unexpected HTML attributes
  • Corruption of the HTML structure
  • Potential cross-site scripting (XSS) if combined with unsafe usage patterns

This issue affects applications that pass untrusted input as JSX attribute keys during server-side rendering.

References

@yusukebe yusukebe published to honojs/hono Apr 15, 2026
Published to the GitHub Advisory Database Apr 16, 2026
Reviewed Apr 16, 2026
Last updated Apr 16, 2026

Severity

Moderate

CVSS overall score

This score calculates overall vulnerability severity from 0 to 10 and is based on the Common Vulnerability Scoring System (CVSS).
/ 10

CVSS v3 base metrics

Attack vector
Network
Attack complexity
Low
Privileges required
None
User interaction
Required
Scope
Unchanged
Confidentiality
None
Integrity
Low
Availability
None

CVSS v3 base metrics

Attack vector: More severe the more the remote (logically and physically) an attacker can be in order to exploit the vulnerability.
Attack complexity: More severe for the least complex attacks.
Privileges required: More severe if no privileges are required.
User interaction: More severe when no user interaction is required.
Scope: More severe when a scope change occurs, e.g. one vulnerable component impacts resources in components beyond its security scope.
Confidentiality: More severe when loss of data confidentiality is highest, measuring the level of data access available to an unauthorized user.
Integrity: More severe when loss of data integrity is the highest, measuring the consequence of data modification possible by an unauthorized user.
Availability: More severe when the loss of impacted component availability is highest.
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:L/A:N

EPSS score

Weaknesses

Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')

The product does not neutralize or incorrectly neutralizes user-controllable input before it is placed in output that is used as a web page that is served to other users. Learn more on MITRE.

CVE ID

No known CVE

GHSA ID

GHSA-458j-xx4x-4375

Source code

Credits

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