CVE-2026-59895Network attack vector

Server-side XSS via unescaped cx class names

Published Jul 8, 2026 · Updated Jul 8, 2026

Cross-site scripting in Hono 4.0.0 through 4.12.26 allows remote attackers to inject markup through untrusted cx() class names. The hono/css createCssContext path returned cx() output with isEscaped set even though external class-name text had not passed through HTML attribute escaping. Exploitation requires server-side JSX rendering, attacker control of a class name, and a victim to load the response, enabling script execution in that browser session.

CVSS severity6.1
Medium
EPSS probability0.33%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Cross-site scripting in Hono 4.0.0 through 4.12.26 allows remote attackers to inject markup through untrusted cx() class names. The hono/css createCssContext path returned cx() output with isEscaped set even though external class-name text had not passed through HTML attribute escaping. Exploitation requires server-side JSX rendering, attacker control of a class name, and a victim to load the response, enabling script execution in that browser session.

The record

CVE
CVE-2026-59895
Published
Jul 8, 2026
Updated
Jul 8, 2026
Vendor
Hono
Product
Hono
Classifications
CWE-79, CWE-116, T1189
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jul 8, 2026CVE publishedPublication date reported by the CVE source.
  2. Jul 8, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=>= 4.0.0, < 4.12.27

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Hono · Honoversion=>= 4.0.0, < 4.12.27

Published CVSS scores

6.1GitHubCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-79Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
CWE-116Improper Encoding or Escaping of Output
T1189Drive-by Compromise

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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