Low severityNVD Advisory· Published Mar 12, 2026· Updated Mar 12, 2026
Unhead has a Bypass of URI Scheme Sanitization in makeTagSafe via Case-Sensitivity
CVE-2026-31873
Description
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.
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Affected packages
Versions sourced from the GitHub Security Advisory.
| Package | Affected versions | Patched versions |
|---|---|---|
unheadnpm | < 2.1.11 | 2.1.11 |
Affected products
2Patches
Vulnerability mechanics
References
4- github.com/advisories/GHSA-5339-hvwr-7582ghsaADVISORY
- nvd.nist.gov/vuln/detail/CVE-2026-31873ghsaADVISORY
- github.com/unjs/unhead/releases/tag/v2.1.11ghsaWEB
- github.com/unjs/unhead/security/advisories/GHSA-5339-hvwr-7582ghsax_refsource_CONFIRMWEB
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