CVE-2026-6551 is a stored cross-site scripting vulnerability in the Timeline Blocks for Gutenberg WordPress plugin (versions up to 1.1.10). The issue occurs due to improper neutralization of input in the 'titleTag' attribute of the timeline-blocks/tb-timeline-blocks block, allowing authenticated users with contributor-level privileges or higher to inject arbitrary web scripts. These scripts execute in the context of users viewing the injected pages, potentially leading to session hijacking or other script-based attacks. The vulnerability has a CVSS 3.1 base score of 6.4 (AV:N/AC:L/PR:L/UI:N/S:C/C:L/I:L/A:N), reflecting network attack vector, low attack complexity, required privileges, no user interaction, and partial impact on confidentiality and integrity.

An attacker with contributor-level or higher access can exploit this vulnerability to inject persistent malicious scripts into pages using the vulnerable block attribute. When other users access these pages, the injected scripts execute in their browsers, potentially compromising user sessions or performing unauthorized actions within the context of the affected site. The impact affects confidentiality and integrity but does not affect availability. There are no known exploits in the wild at this time.

Patch status is not yet confirmed — check the vendor advisory for current remediation guidance. Until an official fix is available, restrict contributor-level access to trusted users only and consider removing or disabling the Timeline Blocks for Gutenberg plugin if feasible. Monitor vendor channels for updates and apply patches promptly once released.