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Vulnerabilities

Vulnerability · CVE-2026-99170

CVE-2026-99170: namespace: a mount that copy_tree() leaves out can't take over a lock

Published Oct 28, 2026 · catalog updated Nov 1, 2026 · Linux Linux

Last checked Nov 4, 2026. A connected source was read within the last 7 days.

Check if you run it

No confirmed exploitation is on record for CVE-2026-99170. EPSS is 0.13%. Act only if a listed version of Linux Linux is installed.

Gaps on this record

  • No vendor fix or required action is stored. Compare the linked advisory before you change production.

Same product and reporting

Severity
High8.8
Known exploitation
Not in CISA/VulnCheck KEV
EPSS
0.13%
Remediation
Advisory link
Affected products
Linux Kernel · linux kernel · vendor Linux Linux

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/ /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 moun

Are you affected?

Enter the version you run. The result uses only the ranges stored on this record.

The check returns affected, not affected, or incomplete. It does not guess a version that is missing from the record.

  • Linux Kernel7.1.0 → 7.2.13
  • linux kernelversion unspecified
  • vendor Linux Linuxversion unspecified

How to fix CVE-2026-99170

What to do

Three questions, each answered from this record only. Confirm the vendor advisory before you patch.

Should you patch?

No confirmed exploitation is on record for CVE-2026-99170. EPSS is 0.13%. Act only if a listed version of Linux Linux is installed.

Which versions are affected?

Compare what you have installed with Kernel 7.1.0 → 7.2.13. Compare the installed version with the linked vendor advisory before you change production.

What should an analyst verify?

No weakness class is stored. EPSS 0.13%. There is no CISA KEV listing. No Exploit-DB or Metasploit reference is linked. Use the source links for the original advisory.

Code

The project this record applies to. Exploit listings stay in References.

Timeline

Detection, updates, and resolution for this record.

  1. Oct 28, 2026 · Tenable CVE Database

    Detected

    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 lon

  2. Oct 28, 2026 · CVE.org

    Updated

    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 lon

  3. Nov 1, 2026 · OpenSSF OSV / OSV Scanner

    Fix available

    Kernel fixed in 7.2.13

  4. Nov 1, 2026 · OpenSSF OSV / OSV Scanner

    Fix available

    Kernel fixed in 7.2.13

  5. Nov 1, 2026 · OpenSSF OSV / OSV Scanner

    Updated

    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 lon

Sources

  • BSI CERT-BundGovernment advisoryCVE-2026-99170

    Linux Kernel: Mehrere Schwachstellen ermöglichen nicht spezifizierten Angriff

    wid.cert-bund.de
  • CVE.orgVulnerability recordCVE-2026-99170

    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 t

    cve.org
  • FIRST EPSSExploitation probabilityCVE-2026-99170

    30-day exploitation probability 0.13%

    first.org
  • Linux Kernel CVEVendor advisoryCVE-2026-99170

    From: Greg Kroah-Hartman Description =========== 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 be

    git.kernel.org
  • OpenSSF OSV / OSV ScannerPackage advisoryCVE-2026-99170

    namespace: a mount that copy_tree() leaves out can't take over a lock

    osv.dev
  • Tenable CVE DatabaseVulnerability recordCVE-2026-99170

    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 lon

    tenable.com

References

Freshness

Last verified in this catalog Nov 4, 2026. Significant claims (KEV, EPSS, CVSS, affected ranges) come from the source rows above — open the original publisher for the authoritative advisory.

  • FIRST EPSSNov 4, 2026
  • Tenable CVE DatabaseNov 1, 2026
  • OpenSSF OSV / OSV ScannerNov 1, 2026
  • BSI CERT-BundOct 30, 2026
  • CVE.orgOct 29, 2026
  • Linux Kernel CVEOct 28, 2026