CVE-2026-126359: Hono: `css` helper does not escape a closing tag split between the template and an interpolated value, allowing HTML injection

CVE-2026-126359 · Severity: low · CVSS 3.4 · Published 2026-11-13

Hono is a Web application framework that provides support for any JavaScript runtime. From 3.12.0 until 4.13.16, the css helper in hono/css escapes interpolated string values separately and therefore fails to neutralize a closing style tag when < ends the template text or a preceding value and / begins the next attacker-controlled value. During server-side rendering, the combined output can close the <Style /> element early and cause the remainder of the interpolated value to be interpreted as HTML. Applications that place an untrusted string immediately after < in a css template, including adjacent untrusted interpolations, can expose viewers to attacker-controlled HTML or script and information accessible to that page. Other uses of the css helper are not affected. This issue is fixed in version 4.13.16.

Technologies: hono (npm). Vendors: npm.

Quick answers

Is CVE-2026-126359 exploited in the wild?
No. Junglewise Threat Intelligence has no report of CVE-2026-126359 being exploited in the wild.
How severe is CVE-2026-126359?
Low severity, with a CVSS score of 3.4, published 13 November 2026.
Which products and versions are affected?
hono (npm) >= 3.12.0, <= 4.13.15, SEMVER:introduced=3.12.0,fixed=4.13.16.
Is there a fix for CVE-2026-126359?
Yes. hono (npm): upgrade to 4.13.16 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
Am I affected by CVE-2026-126359?
Check whether you run hono (npm) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

How to fix

  • hono (npm): upgrade to 4.13.16 or later
    npm install hono@4.13.16

Affected products

  • hono (npm) >= 3.12.0, <= 4.13.15, SEMVER:introduced=3.12.0,fixed=4.13.16

Identifiers

  • CVE-2026-126359
  • GHSA-3gg2-335m-rxc6

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