CVE-2026-31873: Unjs Unhead

Medium severity, CVSS 6.1. EPSS: 0.3% chance of exploitation in the next 30 days.

Unhead is a document head and template manager. Prior to 2.1.11, The link.href check in makeTagSafe (safe.ts) uses String.includes(), which is case-sensitive. Browsers treat URI schemes case-insensitively. DATA:text/css,... is the same as data:text/css,... to the browser, but 'DATA:...'.includes('data:') returns false. An attacker can inject arbitrary CSS for UI redressing or data exfiltration via CSS attribute selectors with background-image callbacks. This vulnerability is fixed in 2.1.11.

Affected products

• Unjs Unhead: before 2.1.11 (fixed in 2.1.11)

Published 2026-03-12. Last modified 2026-06-17.