CVE-2026-31860: Unhead has a XSS bypass in `useHeadSafe` via attribute name injection and case-sensitive protocol check

Severity: medium (CVSS 6.1 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.3% probability of exploitation in the next 30 days
Public exploit or detection template: yes
Published: 2026-03-12 · updated 2026-06-17
Weakness: CWE-79

Description

Unhead is a document head and template manager. Prior to 2.1.11, useHeadSafe() can be bypassed to inject arbitrary HTML attributes, including event handlers, into SSR-rendered <head> tags. This is the composable that Nuxt docs recommend for safely handling user-generated content. The acceptDataAttrs function (safe.ts, line 16-20) allows any property key starting with data- through to the final HTML. It only checks the prefix, not whether the key contains spaces or other characters that break HTML attribute parsing. This vulnerability is fixed in 2.1.11.

Affected products

unjs unhead: before 2.1.11 — fixed in 2.1.11

How to fix

Upgrade to a fixed version: unjs unhead 2.1.11. Check the vendor advisory for mitigations.

References

Get alerted when CVE-2026-31860 or the next vulnerability affects your stack