Linux Kernel up to 7.2.12 Namespace copy_tree privileges management

Summaryinfo

A vulnerability, which was classified as very critical, was found in Linux Kernel up to 7.2.12. This affects the function copy_tree of the component Namespace. The manipulation results in privileges management. This vulnerability is reported as CVE-2026-99170. The attack requires a local approach. No exploit exists. You should upgrade the affected component.

Detailsinfo

A vulnerability classified as very critical has been found in Linux Kernel up to 7.2.12. Affected is the function copy_tree of the component Namespace. The manipulation with an unknown input leads to a privileges management vulnerability. CWE is classifying the issue as CWE-269. The product does not properly assign, modify, track, or check privileges for an actor, creating an unintended sphere of control for that actor. This is going to have an impact on confidentiality, integrity, and availability. CVE summarizes:

In the Linux kernel, the following vulnerability has been resolved: namespace: a mount that copy_tree() leaves out can't take over a lock Since commit c62a4766937e ("move_mount: transfer MNT_LOCKED") a mount can be moved beneath a locked mount. The lock moves from the old cover to the new mount which takes over the job of hiding what's under it and the old cover can be unmounted. That works as long as the new mount stays. But the caller picks the new mount and copy_tree() leaves a mount of a mount namespace file out of every copy made without CL_COPY_MNT_NS_FILE, together with everything mounted on it, and never looks at MNT_LOCKED. unshare(CLONE_NEWNS) and mount propagation make such copies. So a task that is root in its own user namespace gets rid of a locked cover on a file without a race and without touching the filesystem below it. It makes a child with a mount namespace of its own, binds the child's /proc/<pid>/ns/mnt beneath the cover with MOVE_MOUNT_BENEATH, which hands the lock to that bind, and calls unshare(CLONE_NEWNS). The new mount namespace has nothing on the file. That's the usual way to mask a single file, a bind of /dev/null or of an empty file. With a bind of an ordinary file the file stays covered. copy_tree() already refuses to leave out a locked unbindable mount with -EPERM since commit df7342b24018 ("mount: Don't allow copying MNT_UNBINDABLE|MNT_LOCKED mounts"). Do the same for a locked mount of a mount namespace file. That also covers a tree copied with CL_COPY_MNT_NS_FILE and attached into a mount namespace of another user namespace where lock_mnt_tree() locks it. Note that unshare(CLONE_NEWNS) and clone(CLONE_NEWNS) fail with EPERM from such a mount namespace from then on. The mount can't be left out and it can't be unmounted. And refuse to move a mount of a mount namespace file beneath a locked mount in the first place. Otherwise the task ends up with a mount it can't unmount and an unshare() that fails for good. Chris also found a second mount that goes away by itself, a clone of an automounted mount that shrink_submounts() took along with its parent. Commit f78ddcc87224 ("namespace: never expire a locked mount") took care of that one. Chris's reproducer is appended. Mode nsfile reads SECRET after the unshare() on 7.3-rc7, with this patch the move_mount() fails with EINVAL and the file stays covered. nsfile-control uses an ordinary file and reads MASK both ways. // SPDX-License-Identifier: GPL-2.0 /* * Get rid of a locked cover with MOVE_MOUNT_BENEATH. * * The "admin" (root) makes a tmpfs W: * W/D file, holds SECRET, covered by a bind of a file with MASK * W/Dd/inner file, holds SECRET, Dd is covered by a bind of a directory * whose "inner" holds MASK * W/own directory of uid 1000 with the file "mine" and the * directory "minedir", whose "inner" holds MINE * W/dbg debugfs, mode 755. dbg/tracing is an automount point * The "attacker" is uid 1000. It enters a new user namespace with a new mount * namespace, so W and both covers are locked there. * * usage: prog MODE * plain put a bind of own/mine beneath the cover of D, unmount the cover * nsfile put a bind of the mount namespace file of a child beneath the * cover of D, then unshare(CLONE_NEWNS) * nsfile-control the same with a bind of own/mine * shrink put a bind of the automounted tracefs beneath the cover of Dd, * unmount the cover, put a tmpfs beneath W, call umount(W), which fails * shrink-control the same with a bind of own/minedir * The environment variable AUTOMOUNT_DIR names another automount point for "shrink". */ #define _GNU_SOURCE #include <errno.h> #include <fcntl.h> #include <grp.h> #include <sched.h> #include <signal.h> #include <stdio.h> #include <stdlib.h> #include <string.h> #include <unistd.h> ---truncated---

The advisory is available at git.kernel.org. This vulnerability is traded as CVE-2026-99170 since 09/25/2026. The exploitability is told to be easy. Local access is required to approach this attack. Technical details are known, but there is no available exploit. The structure of the vulnerability defines a possible price range of USD $0-$5k at the moment (estimation calculated on 10/28/2026). This vulnerability is assigned to T1068 by the MITRE ATT&CK project.

Upgrading to version 7.2.13 eliminates this vulnerability. Applying the patch bd71d33923b9d6216bcee44331dd37142b0a8441/69fbe94f80bc423613fa18dae6656757423732a2 is able to eliminate this problem. The best possible mitigation is suggested to be upgrading to the latest version.

If you want to get best quality of vulnerability data, you may have to visit VulDB.

Productinfo

Type

• Operating System

Vendor

• Linux

Name

• Kernel

Version

• 7.2.0
• 7.2.1
• 7.2.2
• 7.2.3
• 7.2.4
• 7.2.5
• 7.2.6
• 7.2.7
• 7.2.8
• 7.2.9
• 7.2.10
• 7.2.11
• 7.2.12

License

• open-source

Website

• Vendor: https://www.kernel.org/

CPE 2.3info

• 🔒
• 🔒
• 🔒

CPE 2.2info

• 🔒
• 🔒
• 🔒

CVSSv4info

CVSSv3info

CVSSv2info

Exploitinginfo

Threat Intelligenceinfo

Countermeasuresinfo

Timelineinfo

Sourcesinfo

Entryinfo

If you want to get best quality of vulnerability data, you may have to visit VulDB.

Discussion