CVE-2026-89560
HighCVSS 8.4Exploitation Probability (EPSS)
Low risk2th percentile - higher than 2% of all known CVEs
Summary
A vulnerability in the Linux kernel's Landlock mechanism related to whiteout object creation used by OverlayFS has been fixed. Creating whiteouts via mknod(2) with S_IFCHR and makedev(0,0), and via renameat2(2) with RENAME_WHITEOUT, was not properly restricted by Landlock permissions, allowing bypass of restrictions. The fix requires LANDLOCK_ACCESS_FS_MAKE_REG for both cases.
Risk Assessment
The flaw allowed a process confined by Landlock to create directory entries (whiteouts) without the required permissions, potentially breaking sandbox isolation. In environments relying on Landlock to restrict untrusted processes, this could enable manipulation of the OverlayFS filesystem view.
Recommendation
Update the Linux kernel to a version containing this fix. If not possible, consider restricting access to mknod(2) and renameat2(2) with RENAME_WHITEOUT for Landlock-confined processes.
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Original NVD description (English source)
In the Linux kernel, the following vulnerability has been resolved: landlock: Require LANDLOCK_ACCESS_FS_MAKE_REG for whiteout creation Whiteout objects are used in the upper layer of an OverlayFS to indicate that the file with this name does not exist in the unified view, even if it is present in one of the lower layer file systems. For the userspace implementations of OverlayFS (fuse-overlayfs), whiteout objects can be created from userspace as well: * mknod(2) with S_IFCHR and makedev(0, 0) * renameat2(2) with RENAME_WHITEOUT, creating the whiteout in the old place of the moved file. This commit guards whiteout creation in both of these cases with LANDLOCK_ACCESS_FS_MAKE_REG. Whiteout objects are *not* considered character devices and are not bound to a driver. LANDLOCK_ACCESS_FS_MAKE_REG describes the same permission class as a whiteout object: creating one is the only S_IFCHR creation that the VFS exempts from CAP_MKNOD, so it is as unprivileged as creating a regular file, while LANDLOCK_ACCESS_FS_MAKE_CHAR and LANDLOCK_ACCESS_FS_MAKE_BLOCK keep meaning the creation of devices that expose a kernel interface [1]. For the mknod(2) case, introduce a Landlock erratum. The creation of whiteout objects through mknod(2) was previously guarded using LANDLOCK_ACCESS_FS_MAKE_CHAR, and it is now guarded using LANDLOCK_ACCESS_FS_MAKE_REG. For the renameat2(2) case, fix a bug: Before this commit, renameat2(2) with RENAME_WHITEOUT would create a directory entry even when all LANDLOCK_ACCESS_FS_MAKE_* rights were denied. This does not affect normal renames within layered OverlayFS mounts: When doing a regular rename() on a mounted fuse-overlayfs, it is the fuse-overlayfs daemon that exercises renameat2() with RENAME_WHITEOUT, and only the Landlock domain of that daemon is checked there. Depends-on: 49c9e09d9610 ("landlock: Fix handling of disconnected directories") Depends-on: fe72ce6710cb ("landlock: Add errata documentation section") [mic: Record why LANDLOCK_ACCESS_FS_MAKE_REG is the matching right, and add link(2) to the user doc]
Vulnerability data from NVD (NIST) · CISA KEV · EPSS