CVE-2026-89560
—Landlock sandbox bypass via OverlayFS whiteout creation in Linux kernel
A flaw in the Linux kernel's Landlock security module lets a sandboxed process bypass file-creation restrictions when creating OverlayFS whiteout objects. Specifically, renameat2(2) with RENAME_WHITEOUT would create a directory entry (a whiteout) even when all LANDLOCK_ACCESS_FS_MAKE_* rights were denied, and whiteouts created via mknod(2) were checked against the wrong permission class (LANDLOCK_ACCESS_FS_MAKE_CHAR instead of LANDLOCK_ACCESS_FS_MAKE_REG). A local attacker with low privileges running inside a Landlock sandbox can exploit this to create whiteouts in an OverlayFS upper layer, effectively hiding files from the unified view and causing integrity and availability impacts (CVSS 8.4, local vector, no confidentiality impact). Affected systems are Linux machines running Landlock-sandboxed workloads combined with OverlayFS, notably userspace implementations such as fuse-overlayfs used by rootless container setups; normal renames on a mounted fuse-overlayfs are not directly affected because the daemon's own Landlock domain is checked. No public proof of concept exists and the issue is not listed in CISA's KEV, so exploitation status is none known.
What to do: Patch to a kernel release containing this Landlock fix (and its dependency commits 49c9e09d9610 and fe72ce6710cb) once available from your distro. Until then, audit whether any Landlock-sandboxed workloads (e.g., rootless container runtimes using fuse-overlayfs) can invoke renameat2(2) with RENAME_WHITEOUT or mknod(2) against OverlayFS upper layers, and apply supplementary controls (e.g., seccomp filtering of these syscalls or filesystem ACLs) rather than relying on Landlock alone to deny whiteout creation.
| Linux kernel (Landlock LSM, OverlayFS whiteout handling) | — |
Order-of-magnitude estimate by the model from install counts, market share and public scan data it knows; verify before quoting.
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]
- Vector
- CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:N/I:H/A:H
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