The Linux kernel memfd feature uses seals to restrict modifications. When SEAL_EXEC is added, SEAL_WRITE is implicitly applied to enforce a write-protection policy (W^X). However, the original implementation applied the implied SEAL_WRITE after the check that denies writable mappings, allowing writable mappings to exist despite the seal. This flaw permits an attacker to present a memfd as write-sealed while retaining writable access, violating the seal's contract. The fix involves applying the implied seals before the writable mapping denial check, restoring the intended protection.

An attacker could exploit this vulnerability to modify memfd contents that are supposed to be write-protected by SEAL_WRITE, potentially undermining security mechanisms relying on memfd immutability guarantees. This could affect processes or components that depend on memfd seals to enforce memory protection policies.

Patch status is not yet confirmed — check the vendor advisory for current remediation guidance. Since this is a kernel vulnerability, monitor official Linux kernel advisories for patches addressing CVE-2026-63952 and apply updates promptly once available.