The vulnerability identified as CVE-2026-1228 affects the WordPress plugin 'Timeline Block – Beautiful Timeline Builder for WordPress (Vertical & Horizontal Timelines)' developed by bplugins. This plugin allows users to create vertical and horizontal timelines on WordPress sites. The flaw is an Insecure Direct Object Reference (IDOR) vulnerability classified under CWE-639, caused by insufficient validation of a user-controlled key parameter within the tlgb_shortcode() function. Specifically, the plugin fails to properly verify authorization when processing the 'id' attribute supplied to the 'timeline_block' shortcode. As a result, any authenticated user with Author-level access or higher can manipulate this parameter to retrieve private timeline content that should otherwise be restricted. The vulnerability does not require user interaction and can be exploited remotely over the network. The CVSS v3.1 base score is 4.3 (medium severity), reflecting the vulnerability's limited impact on confidentiality without affecting integrity or availability. No patches or fixes have been published at the time of disclosure, and no known exploits have been observed in the wild. The vulnerability affects all versions up to and including 1.3.3 of the plugin. This issue highlights the importance of proper access control checks on user-supplied identifiers in WordPress plugins, especially those that expose potentially sensitive content via shortcodes.

For European organizations, the primary impact of this vulnerability is unauthorized disclosure of private timeline content managed through the affected WordPress plugin. This could lead to leakage of sensitive project timelines, internal event histories, or other confidential information embedded in timelines, potentially harming organizational confidentiality and competitive positioning. While the vulnerability does not allow modification or deletion of data, the exposure of private content may violate data protection policies or contractual confidentiality obligations. Organizations relying on WordPress sites with this plugin, particularly those with multiple authors or contributors, face increased risk of insider threat exploitation or accidental data leaks. The impact is more pronounced for sectors handling sensitive timelines such as government agencies, research institutions, and enterprises with intellectual property concerns. Since exploitation requires authenticated Author-level access, the threat is mitigated somewhat by internal access controls but remains significant in environments with many contributors or weak user management. No availability or integrity impacts are expected, and no known active exploitation reduces immediate urgency but does not eliminate risk.

European organizations should immediately audit their WordPress installations to identify the presence of the Timeline Block plugin and determine the plugin version. Until an official patch is released, administrators should restrict Author-level access to trusted users only, minimizing the number of users who can exploit this vulnerability. Implementing strict role-based access controls and reviewing user permissions can reduce exposure. Additionally, organizations can temporarily disable or remove the plugin if timeline functionality is not critical. For sites requiring the plugin, consider implementing web application firewall (WAF) rules to detect and block suspicious shortcode parameter manipulations targeting the 'id' attribute. Monitoring logs for unusual shortcode usage patterns or access to timeline content by unexpected users can help detect exploitation attempts. Once a patch becomes available, prioritize immediate plugin updates. Finally, educate content authors and administrators about the risks of unauthorized access and enforce strong authentication mechanisms to prevent credential compromise.