The Linux kernel vulnerability CVE-2026-64514 concerns the userfaultfd interface's must_wait writability check on page table entries (PTEs). The affected functions read PTEs without acquiring the page table lock and apply write checks that only decode bits valid for present entries. When encountering swap or migration entries, these functions misinterpret offset bits as write bits, resulting in undefined behavior. This can cause a thread to remain asleep indefinitely, waiting for a wake event that may never occur. The fix involves gating the writability check on the presence of the PTE, ensuring that only present entries are checked for writability, and non-present entries return a 'don't wait' result to allow fault path retries.

The vulnerability can cause threads to stall indefinitely by waiting on a write protection block that is incorrectly detected due to misinterpreted PTE bits. This may lead to denial of service conditions where userfaultfd-related threads do not progress as expected. There is no indication of code execution or privilege escalation from the provided data.

Patch status is not yet confirmed — check the vendor advisory for current remediation guidance. Since this is a Linux kernel vulnerability, monitor official Linux kernel security advisories for patches addressing CVE-2026-64514. Apply the official kernel updates once available to resolve the issue.