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Fencer Vulns
medium 6.1

CVE-2026-59895 json

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

published 2026-07-08 4 mo ago modified 2026-10-25 14 d ago also GHSA-w62v-xxxg-mg59 , EUVD-2026-42327

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 25%
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

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
4 mo ago

Exploit prediction

0.33% chance of exploitation in the next 30 days, higher than 25% of all scored CVEs (FIRST EPSS, 2026-11-08).

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 Vulns 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.