Case-Sensitive URI Scheme Check in Unhead Document Management System

CVE-2026-31873

What is CVE-2026-31873?

The Unhead document head and template manager has a vulnerability where the check for URI schemes is case-sensitive. This flaw allows attackers to exploit the system by injecting arbitrary CSS for user interface redressing or extracting data through CSS attribute selectors. Given that browsers interpret URI schemes in a case-insensitive manner, an attacker can bypass the security check and craft malicious data URLs with 'DATA:text/css,...', facilitating unauthorized access and data leakage. This vulnerability was remedied in version 2.1.11.

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