The Linux kernel vulnerability CVE-2026-68448 concerns the overlayfs filesystem's handling of the copy_file_range operation across different overlayfs mounts. The flaw arose because the read permission check for the source file was performed using the destination overlayfs mounter credentials instead of the source overlayfs mounter credentials. This could lead to unauthorized read access or denial of legitimate access during cross-submount copy operations. The issue was fixed by explicitly verifying read access with the source overlayfs mounter credentials, correcting the permission check logic.

This vulnerability could allow unauthorized read access to files during cross-overlayfs copy operations or cause denial of access to otherwise permitted copy operations. However, the denial of access is considered a quirk with fallback options available in userspace, so no significant harm is expected from that side. The unauthorized read access scenario represents a potential confidentiality breach within affected overlayfs environments.

A fix has been implemented in the Linux kernel to explicitly verify read access to the source file using the correct source overlayfs mounter credentials. Users should apply the official kernel updates that include this fix. Since this is a kernel-level vulnerability, updating to a patched kernel version is the recommended remediation. No additional mitigations are indicated by the vendor advisory.