Cloudanix VulnDB

CVE-2026-89560

High · 8.4

CVSS

8.4

EPSS

0.1%

Published

Sep 11, 2026

CISA due date

—

Cloudanix analysis

Next patch cycle SSVC: Track

A flaw in Linux access controls could let programs that should be restricted create markers that hide files inside layered filesystems.

Exploitation
Local Privilege
Attacker needs
Low Privilege
Complexity
Low
Impact
Privilege Gain
Component
OS kernel
Class
Authorization Bypass
Remediation
Upgrade
Effort
Medium
Patch risk
Low

What it actually does

Landlock previously enforced whiteout creation via LANDLOCK_ACCESS_FS_MAKE_CHAR (for mknod) or failed to enforce any MAKE_* right (for renameat2 RENAME_WHITEOUT), allowing processes lacking LANDLOCK_ACCESS_FS_MAKE_REG to create OverlayFS whiteouts.

Why it matters to the business

Restricted processes could alter file visibility in layered filesystems, enabling unauthorized hiding or exposure of files and undermining container or application sandboxing controls.

How an attack unfolds

An attacker obtains a Landlock-restricted process, invokes mknod(2) with S_IFCHR and makedev(0,0) or renameat2(2) with RENAME_WHITEOUT on an OverlayFS mount, and succeeds in creating a whiteout even when the policy denies MAKE_REG, thereby manipulating the unified directory view.

How to fix it

Upgrade the Linux kernel to a version containing the Landlock commit that requires LANDLOCK_ACCESS_FS_MAKE_REG for whiteout creation and records the erratum for prior MAKE_CHAR behavior.

How to confirm the fix worked

Confirm the running kernel includes the referenced Landlock erratum and test that a policy denying MAKE_REG now correctly blocks both mknod whiteouts and RENAME_WHITEOUT operations.

Typical attack path

  1. Obtain code execution inside a Landlock-sandboxed process
  2. Locate an OverlayFS mount writable by that process
  3. Call mknod(2) or renameat2(2) with RENAME_WHITEOUT to create a whiteout
  4. Observe or exploit the resulting change in file visibility across layers

How to detect it

Review kernel audit logs for Landlock policy violations involving MAKE_CHAR or unexpected directory-entry creation via renameat2 on OverlayFS mounts; correlate with process sandboxing events.

What your security team should do

  • Apply kernel updates that enforce the corrected Landlock whiteout rule
  • Audit existing Landlock policies and add MAKE_REG where whiteout creation must be controlled
  • Include OverlayFS mount points in runtime policy testing

The record

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]

Affected packages

Ecosystem Package Introduced Fixed