CVE-2026-44458 — hono
MEDIUMCVE-2026-44458 is a medium-severity (CVSS 4.3) CWE-74 vulnerability in hono. A fix is available for hono — see the affected versions and patch details below.
Hono: CSS Declaration Injection via Style Object Values in JSX SSR
Exploitation Status
No confirmed exploitation observed yet
- CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.
Exploitation and automatability from CISA’s SSVC triage for CVE-2026-44458.
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
Where this sits among everything scored
Real-World Exposure
How broadly this vulnerability is actually deployed: weekly install volume shows current usage, and reverse-dependency count shows how many other packages break if it stays unpatched.
hononpmDescription
Summary
The JSX renderer escapes style attribute object values for HTML but not for CSS. Untrusted input in a style object value or property name can therefore inject additional CSS declarations into the rendered style attribute. The impact is limited to CSS and does not allow JavaScript execution or HTML attribute breakout.
Details
style object values are serialized into a CSS declaration list and escaped for HTML attribute context only. Characters that act as CSS declaration boundaries — such as ;, comment markers, quoted strings, and block delimiters — are valid in HTML attribute content and can extend a value beyond its assigned property.
This issue arises when untrusted input is interpolated into a JSX style object and rendered server-side.
Impact
An attacker who can control the value or property name of a style object may inject arbitrary CSS declarations. This may lead to:
- Visual manipulation of the page, including full-viewport overlays usable for phishing
- Outbound requests to attacker-controlled hosts via CSS resource references such as
url(...) - Hijacking of UI affordances through layout, positioning, or visibility changes
This issue affects applications that render JSX on the server with style object values or property names derived from untrusted input.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 📦npm | hono | all versions | 4.12.18npm install hono@4.12.18 |
Affected Products
honohonoDetection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for hono, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update hono to 4.12.18 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-44458 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
Frequently Asked Questions
Is CVE-2026-44458 in your dependencies?
Find it across npm, including transitive dependencies.