CVE-2026-3906: WordPress 6.9 - 6.9.1 - Missing Authorization to Authenticated (Subscriber+) Arbitrary Note Creation via REST API

WordPress core is vulnerable to unauthorized access in versions 6.9 through 6.9.1. The Notes feature (block-level collaboration annotations) was introduced in WordPress 6.9 to allow editorial comments directly on posts in the block editor. However, the REST API createitempermissionscheck() method in the comments controller did not verify that the authenticated user has editpost permission on the target post when creating a note. This makes it possible for authenticated attackers with Subscriber-level access to create notes on any post, including posts authored by other users, private posts, and posts in any status.