The 'authorized attacker' qualifier in CVE-2026-63512 tells you something critical that the CVSS 6.5 score obscures: this isn't a vulnerability with a window between patch release and exploit availability. The exposure started when the permissions were granted—and in mature SharePoint deployments, that's often years ago.
This is a tampering vulnerability in SharePoint's fine-grained permission model. The mechanism is a missing authorization check in a code path that validates authentication but fails to verify whether the user's permissions extend to the specific modification being requested. SharePoint's architecture layers permissions across site collections, sites, lists, libraries, and items—and the code paths that operate across these boundaries (moving content, modifying metadata, adjusting permissions) are where these gaps emerge.
Here's what matters operationally: the authorized user population in any SharePoint deployment older than a few years is not stable. Service accounts accumulate rights across migrations. Permissions granted for temporary projects persist after those projects end. Delegated access compounds. An attacker exploiting this gap doesn't need to escalate—they need to already be inside, and 'inside' is far larger than the CVE assumes.
The CVSS 6.5 reflects a narrow exploitation window in Microsoft's testing environment—a specific role, a specific content type, a specific API path. In the field, the blast radius is measured by how many authorized users exist, how long they've held those permissions, and whether any of those permissions involve cross-boundary operations or inheritance chains. This is why similar authorization failures cluster around metadata modification and inheritance manipulation: those are the operations where one missing check cascades the farthest.
What to do: treat this as a permission-auditing trigger, not just a patch to deploy. Identify users with write or modify permissions across site boundaries, review permissions granted for temporary purposes, and verify that inheritance chains haven't been altered in ways that propagated access beyond intent. The patch fixes one code path; the risk lives in the accumulated permission surface.