CVE-2026-31873
An attacker can inject arbitrary CSS for UI redressing or data exfiltration via CSS attribute selectors with background-image callbacks.
Does this matter?
Lower severity and a low EPSS score (0.24%). Track it; it rarely justifies an emergency change on its own.
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.
- CVSS 3.1
- 6.1 MEDIUMCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
- EPSS
- 0.24% probability · 15th percentile
- CISA KEV
- Not listed
- Weakness
- CWE-79
- Affected
- unjs/unhead
- Source
- security-advisories@github.com
References
- https://github.com/unjs/unhead/security/advisories/GHSA-5339-hvwr-7582Exploit, Mitigation, Vendor Advisory
Source: NVD record, EPSS from FIRST.org, KEV from CISA. Refreshed daily.