CVE-2026-6551 is a stored cross-site scripting vulnerability in the Timeline Blocks for Gutenberg WordPress plugin, affecting all versions up to and including 1.1.10. The vulnerability is due to improper neutralization of input in the 'titleTag' attribute of the timeline-blocks/tb-timeline-blocks block, allowing authenticated users with contributor or higher privileges to inject arbitrary web scripts. These scripts execute in the context of users viewing the injected pages, potentially leading to session hijacking or other client-side impacts. The CVSS 3.1 score is 6.4 (medium severity), with attack vector network, low attack complexity, privileges required (low), no user interaction, and scope changed. No official fix or patch has been published by the vendor as of the information provided.

An attacker with contributor-level or higher access can inject persistent malicious scripts into pages via the vulnerable attribute. This can lead to client-side impacts such as theft of user credentials, session tokens, or other sensitive information when other users view the compromised pages. The vulnerability does not affect availability and requires authenticated access, limiting the attack surface. No known active exploitation has been reported.

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. Consider removing or disabling the Timeline Blocks for Gutenberg plugin if feasible. Monitor for updates from the vendor and apply patches promptly once released.