CVE-2026-63952

In the Linux kernel, the following vulnerability has been resolved:

memfd: deny writeable mappings when implying SEAL_WRITE

When SEAL_EXEC is added, SEAL_WRITE is implied to make W^X. But the

implied seal is set after the check that makes sure the memfd can not have

any writable mappings. This means one can use SEAL_EXEC to apply

SEAL_WRITE while having writeable mappings.

This breaks the contract that SEAL_WRITE provides and can be used by an

attacker to pass a memfd that appears to be write sealed but can still be

modified arbitrarily.

Fix this by adding the implied seals before the call for

mapping_deny_writable() is done.