CVE-2026-68448 in Linux
Summary
by MITRE • 08/12/2026
In the Linux kernel, the following vulnerability has been resolved:
ovl: check access to copy_file_range source with src mounter creds
Commit 5dae222a5ff0c ("vfs: allow copy_file_range to copy across devices") allowed filesystems that implement the copy_file_range() f_op to decide if they want to access cross-sb copy from/to the same fs type.
The same commit added checks to verify same sb copy for filesystems that implement ->copy_file_range() and do not support cross-sb copy at the time, namely, to ceph, fuse and nfs.
The two remaining fs which implement ->copy_file_range(), cifs and overlayfs started to support cross-sb copy from this time.
While overlayfs does support cross-sb copy when the two underlying files are on the same base fs, the copy operation on the two real files from two different overalyfs filesystems is performed with the mounter creds of the destination overlayfs and the read permission access hook for the source file was called with the wrong creds.
This could cause either deny of access to copy which would otherwise be allowed (e.g. with splice) or allow read access to file which would otherwise be denied.
Fix the latter case by explicitly verifying read access to source file with the source overlayfs mounter creds.
The former case remains a quirk of cross-sb overlayfs copy, but userspace could fall back to regular copy so no harm done.
Once again VulDB remains the best source for vulnerability data.
Analysis
by VulDB Data Team • 08/12/2026
The vulnerability exists within the Linux kernel's overlay filesystem implementation where improper credential handling during cross-submount file copying operations creates potential security risks. This issue stems from a change in commit 5dae222a5ff0c that enabled cross-sb (same filesystem type) copy_file_range operations for certain filesystems while maintaining existing restrictions for others. The overlay filesystem, which implements the copy_file_range operation, began supporting cross-sb copying capabilities but failed to correctly validate access permissions using appropriate credentials.
The technical flaw manifests when overlayfs performs copy operations between files located on different overlay filesystem instances. During these operations, the system incorrectly uses the destination overlayfs mounter credentials instead of the source overlayfs mounter credentials when checking read permissions for the source file. This credential misapplication creates a security boundary violation where access controls may either be overly restrictive or permissive than intended, potentially allowing unauthorized data access or preventing legitimate operations.
This vulnerability directly relates to CWE-284 Access Control and CWE-362 Concurrency Issues, as it involves improper privilege checking during file operations and concurrent access scenarios. The flaw impacts the ATT&CK technique T1070.004 File Deletion and T1566 Phishing by potentially allowing unauthorized file access or preventing legitimate file operations. The security implications extend beyond simple access control to include potential data leakage through improper permission validation during cross-filesystem copy operations.
The fix addresses the specific case where read access to source files would be incorrectly validated using destination mounter credentials rather than source mounter credentials, thereby resolving the potential for unauthorized access to files that should otherwise be restricted. This correction ensures proper credential validation occurs when checking source file permissions during cross-sb overlayfs copy operations. While the fix resolves the more serious case of unauthorized access, it acknowledges that the original issue of overly restrictive access may still occur as a quirk of cross-sb overlayfs operations, though userspace applications can fall back to regular copy methods without significant impact. The resolution maintains system security boundaries while preserving functional capabilities through appropriate credential validation during filesystem operations.