CVE-2026-59895: Hono is a Web application framework that provides support for any JavaScript runtime

Q: How do I fix CVE-2026-59895?

hono: upgrade to 4.12.27. Exact commands for each OS are on this page.

Q: Is CVE-2026-59895 being exploited?

CVE-2026-59895 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

Q: What does CVE-2026-59895 affect?

CVE-2026-59895 affects hono. Severity is medium (CVSS 6.1). 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 inpu

Q: How urgent is CVE-2026-59895?

Priority 28/100. No elevated risk signals yet.

Routine

MEDIUM 6.1UPGRADE

CVE-2026-59895 is a medium-severity flaw (CVSS 6.1) affecting hono. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

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.

Why this priority

No elevated risk signals yet

A fixed release or distro patch exists.

Risk facts

CVSS score	6.1 (Medium)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	Required
EPSS exploit chance	0.3% (top 74%)
CISA exploited list	No
Weakness	CWE-79, CWE-116
Published	2026-07-08
Last modified	2026-10-25

Publisher (CNA): GitHub, Inc. · Vendor: hono

Last updated 2026-10-25 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-07-08 17:17 UTCPublished CVE record published
2026-10-25 17:10 UTCUpdated Record last modified

hono hono UPGRADE

Affected: >= 4.0.0 and < 4.12.27

Fixed in: 4.12.27

Safe to downgrade to: a release before 4.0.0

1. Check installed version

npm ls hono

2. UPGRADE to 4.12.27

npm install hono@">=4.12.27"

3. If no update is available yet, DOWNGRADE to a release before 4.0.0

npm view hono versions npm install hono@"<4.0.0"

Downgrade risk

Downgrading can break dependent software and may reopen older bugs. Read the distro advisory first and test on a non-production host.

After downgrade

Restart the service, and keep the package held until a fixed release ships.

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2026-59895?

hono: upgrade to 4.12.27. Exact commands for each OS are on this page.

Is CVE-2026-59895 being exploited?

CVE-2026-59895 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2026-59895 affect?

CVE-2026-59895 affects hono. Severity is medium (CVSS 6.1). 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 inpu

How urgent is CVE-2026-59895?

Priority 28/100. No elevated risk signals yet.

Related CVEs

CVE-2026-59896 MEDIUM 6.5 UPGRADE Hono is a Web application framework that provides support for any JavaScript runtime
CVE-2026-59897 MEDIUM 4.8 UPGRADE Hono is a Web application framework that provides support for any JavaScript runtime

References

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