CVE-2026-1098 is a stored Cross-Site Scripting (XSS) vulnerability identified in the CM CSS Columns plugin for WordPress, a tool used to manage CSS column layouts via shortcodes. The vulnerability specifically targets the 'tag' shortcode attribute, which is insufficiently sanitized and escaped before being rendered on pages. This flaw allows authenticated users with Contributor-level permissions or higher to inject arbitrary JavaScript code into pages. Because the malicious script is stored, it executes every time a user accesses the infected page, potentially compromising user sessions, stealing cookies, or performing unauthorized actions on behalf of users. The vulnerability is classified under CWE-79 (Improper Neutralization of Input During Web Page Generation) and has a CVSS 3.1 base score of 6.4, reflecting a medium severity level. The attack vector is network-based (remote), requires low attack complexity, and privileges at the contributor level, but no user interaction is needed for exploitation. The vulnerability affects all versions up to and including 1.2.1 of the plugin. No patches or fixes are currently linked, and no known exploits have been reported in the wild. The vulnerability's scope is confined to WordPress sites using this specific plugin, but given WordPress's widespread use, the potential impact is significant. The stored nature of the XSS increases risk by enabling persistent attacks against site visitors and administrators.

For European organizations, this vulnerability poses a risk primarily to websites running WordPress with the CM CSS Columns plugin installed. Exploitation can lead to session hijacking, unauthorized actions performed with the privileges of logged-in users, defacement, or distribution of malware via injected scripts. Since Contributor-level access is sufficient, attackers who have compromised or registered such accounts can leverage this vulnerability to escalate their impact. This can undermine the integrity and confidentiality of user data and damage organizational reputation. In sectors such as e-commerce, government, and media, where WordPress is commonly used, the impact could disrupt services and erode user trust. The vulnerability does not affect availability directly but can lead to indirect denial of service through site defacement or administrative lockout. The medium CVSS score reflects moderate risk, but the persistent nature of stored XSS and the widespread use of WordPress in Europe elevate the threat level. Organizations with multiple contributors or open registration policies are particularly vulnerable.

Immediate mitigation steps include restricting Contributor-level access to trusted users only and monitoring user-generated content for suspicious inputs. Since no official patch is currently available, administrators should implement manual input validation and output escaping for the 'tag' shortcode attribute in the plugin code to neutralize malicious scripts. Employing Web Application Firewalls (WAFs) with rules to detect and block XSS payloads targeting shortcode parameters can reduce risk. Regularly auditing user roles and permissions to minimize unnecessary contributor accounts is critical. Organizations should also monitor logs for unusual activity related to shortcode usage and user content submissions. Once a vendor patch is released, prompt updating of the plugin is essential. Additionally, educating content contributors about safe content practices and potential risks can help prevent exploitation. Backup and recovery plans should be tested to ensure rapid restoration if an attack occurs.