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Fencer Intel
medium 6.1

CVE-2026-59895 json

Hono: Server-Side XSS via JSX Escaping Bypass in cx() Utility

published 4mo ago modified 17d ago also EUVD-2026-42327 , GHSA-w62v-xxxg-mg59

cvss
6.1
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.3%
EPSS 0.3% chance of exploitation in 30 days, percentile 26%
public exploits
0
none known

Summary

Hono is a Web application framework that provides support for any JavaScript runtime. From 4.0.0 before 4.12.27, cx() in hono/css composes class names from plain strings but marks the result as already escaped without HTML-escaping the input, allowing untrusted className values used in a JSX class attribute during server-side rendering to break out of the attribute and inject arbitrary markup. This issue is fixed in version 4.12.27.

Patch / fix

  • npm hono 4.12.27
  • hono hono 4.12.27

Is CVE-2026-59895 in your dependencies? Fencer shows which of your repositories are affected as soon as an advisory lands, and opens the fix as a pull request.

Check with Fencer

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2026-59895 updated cvss 6.1

hono: Hono: Arbitrary markup injection via improper handling of class names in server-side rendering.

  • Red Hat Migration Toolkit for Applications 8 mta/mta-solution-server-rhel9 Red Hat Ansible Automation Platform 2 ansible-automation-platform-27/mcp-server-rhel9, ansible-automation-platform-tech-preview/mcp-server-rhel9 Red Hat Developer Hub 1 rhdh/rhdh-hub-rhel9 Red Hat OpenShift Dev Spaces devspaces/code-rhel9
    affected: no fix available “Fix deferred”
  • Red Hat Hardened Images grafana12.4, grafana13.1
    not affected: vulnerable code not present

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

CISA SSVC

Exploitation
none
Automatable
no
Technical impact
partial
Assessed
4mo ago

Exploit prediction

0.33% chance of exploitation in the next 30 days, higher than 26% of all scored CVEs (FIRST EPSS, 2026-11-11).

CVSS scores

assigned by version score vector
CNA 3.1 6.1 CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
GitHub 3.1 6.1 CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N

Affected packages

ecosystem package affected fixed in
npm hono
>=4.0.0, <4.12.27
4.12.27

Affected products

  • honojs hono

Classification

Weakness
  • CWE-79 Improper Neutralization of Input During Web Page Generation
  • CWE-116 Improper Encoding or Escaping of Output

References

Sources

Fencer Intel keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.

The maintainers of honojs/hono published their own advisory on GitHub. Reviewed sources take precedence over it.