CVE-2025-4126 is a stored XSS vulnerability in the EG-Series WordPress plugin's [series] shortcode, present in all versions up to 2.1.1. The issue is due to improper neutralization of script-related HTML tags (CWE-80) caused by insufficient sanitization and escaping of user-supplied attributes in the shortcode_title function. Authenticated attackers with contributor or higher privileges on sites using the Classic Editor plugin can inject malicious JavaScript in the titletag attribute, which executes when the page is viewed. This vulnerability allows limited cross-site scripting attacks without requiring user interaction.

An attacker with contributor-level access or higher can inject persistent malicious JavaScript code that executes in the context of users visiting the affected page. This can lead to limited confidentiality and integrity impacts such as theft of session tokens or modification of page content. The vulnerability does not affect availability. The CVSS 3.1 base score is 6.4 (medium severity), reflecting network attack vector, low attack complexity, and no user interaction required.

No official patch or fix is currently available for this vulnerability. Patch status is not yet confirmed — check the vendor advisory for current remediation guidance. Until a fix is released, site administrators should restrict contributor-level access and above to trusted users only and consider disabling the Classic Editor plugin if feasible, as it is a prerequisite for exploitation. Monitoring for suspicious shortcode usage may help detect exploitation attempts.