CVE-2026-31873
Unhead has a Bypass of URI Scheme Sanitization in makeTagSafe via Case-Sensitivity
Vexday Risk Score
3Low
SSVC decision (CISA)
Track
No exploitation signal → monitor
CVSS 0EPSS 0.2%KEV nãoPoC —Nuclei —Metasploit —Patch —
Lifecycle
12 Mar 2026Published on NVD
Recommendation: Monitor — no exploitation signal at the moment.
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.
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:N
Affected products
unjs · unheadWant to know if your infrastructure is exposed to this?
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