HTML injection in Users in Guardian/CMC before 26.1.0

A Stored HTML Injection vulnerability was discovered in the Users functionality due to improper validation of an input parameter. An authenticated user with administrative privileges can create a malicious user whose username contains HTML tags. When a victim attempts to delete a group containing the affected user, the injected HTML renders in their browser, enabling phishing and possibly open redirect attacks. Full XSS exploitation and direct information disclosure are prevented by the existing input validation and Content Security Policy configuration.