CVE-2026-98990 - Vulnerability Details

- namespace: check a submount for references right before unmounting it

Description

In the Linux kernel, the following vulnerability has been resolved:

namespace: check a submount for references right before unmounting it

shrink_submounts() and mark_mounts_for_expiry() first collect all the
mounts they are allowed to unmount and then unmount them.

Whether a mount is busy is decided by propagate_mount_busy() on the
tree. But unmounting the first mount changes the tree that the second
one propagates into. propagate_umount()
moves a surviving overmount off a copy it unmounts and mounts it where
the copy was mounted. If that's where the propagated copy of the second
victim is looked up the overmount becomes a candidate of the second
umount_tree(). It's childless and so trim_one() commits it without
looking at its reference count.

So a synchronous umount pulls out a busy mount that is in use somewhere
else and marks it MNT_SYNC_UMOUNT while it has users:

umount2(/tmp/plshrink/p1, 0) = 0 errno 0
cwd is (unreachable)

The same two umounts requested one after the other fail with EBUSY.
This needs a mount with MNT_SHRINKABLE, i.e., automounted submounts of
NFS, AFS and CIFS or the tracefs mount below debugfs. Bind mounts
inherit the flag.

Check each mount right before it is unmounted under the same hold of
namespace_sem and mount_lock as the umount itself. Make sure that the
algorithm stays linear.

Published: 2026-10-23

Score: 4.1 Medium

EPSS: < 1% Very Low

KEV: No

Impact:

Action:

Analysis

Impact

During the unmount process, the kernel incorrectly allows a busy submount to be detached. The first unmount changes the mount tree, so a subsequent propagation check may misinterpret the busy mount as free and remove it. This behavior can surface as EBUSY errors and may result in the removal of a mount that still has active references, potentially corrupting the filesystem state or leading to kernel instability.

Affected Systems

All Linux kernel releases that use the unmount logic described prior to the patch commit are affected. The vendor list indicates generic Linux kernels; no specific version ranges are provided, so any kernel built with the pre‑patch code is potentially vulnerable. The issue involves automounted submounts of NFS, AFS, CIFS, tracefs, and any bind mounts inheriting the MNT_SHRINKABLE flag.

Risk and Exploitability

Location: requires local privileged access to perform unmount operations, typically CAP_SYS_ADMIN. The CVSS score of 4.1 denotes moderate severity. EPSS <1% indicates low likelihood of exploitation in the wild. The vulnerability is not listed in the CISA KEV. Attackers would need to safely trigger the race condition through coordinated unmount requests on busy MNT_SHRINKABLE mounts to cause mount removal errors or instability.

Default status is the baseline for the product, each version can override it (e.g. patched versions marked unaffected).

Vendor Product Default status Versions

Linux

unaffected

Version	Status	Constraints
`1064f874abc0d05eeed8993815f584d847b72486`	affected	< cda0c4e502a0f74a191471ce100fb061e5ab35d6
`1064f874abc0d05eeed8993815f584d847b72486`	affected	< 3f55f71291e4332983cd63b288d1f2be3c9c08fc
`1064f874abc0d05eeed8993815f584d847b72486`	affected	< 361f59e7f3f9a219fb5567bf9abc8482a154a399
`1064f874abc0d05eeed8993815f584d847b72486`	affected	< f6394281834492c6516a405a348b545ae698a331
`1064f874abc0d05eeed8993815f584d847b72486`	affected	< 6e4012e571867868b545c91ca9d6095fdb709907
`1064f874abc0d05eeed8993815f584d847b72486`	affected	< d73f04e92c1aab78d96ac6cadb234c8a3a373d22
`1064f874abc0d05eeed8993815f584d847b72486`	affected	< 18902a23ef36f83d32bafc58ae2484e6bb4bb8ef
`1064f874abc0d05eeed8993815f584d847b72486`	affected	< 32bf92416614a1e3ff3524fc6b780259c7aad3ef
`5e6ef5ef6eaf690faad3a7c6c665ebf45d7b6ccf`	affected	—
`839d42687dfce0ed0ea2c6bd8d707cc0e276fbe7`	affected	—
`808e83e5add13152bd4a88346487de68395c136b`	affected	—
`6de9d08a9718ee9c12ba6343c50141c2d633e3dc`	affected	—
`4.1.40`	affected	< 4.2
`4.4.54`	affected	< 4.5
`4.9.15`	affected	< 4.10
`4.10.3`	affected	< 4.11

Linux

affected

Version	Status	Constraints
`4.11`	affected	—
`0`	unaffected	< 4.11
`5.10.273`	unaffected	≤ 5.10.*
`5.15.224`	unaffected	≤ 5.15.*
`6.1.191`	unaffected	≤ 6.1.*
`6.6.160`	unaffected	≤ 6.6.*
`6.12.113`	unaffected	≤ 6.12.*
`6.18.57`	unaffected	≤ 6.18.*
`7.2.11`	unaffected	≤ 7.2.*
`7.3`	unaffected	≤ *

No data.

Vendor Product Confidence Versions

Linux

100%

Version	Status	Scheme	Platform
`[1064f874abc0d05eeed8993815f584d847b72486,f6394281834492c6516a405a348b545ae698a331)`	affected	code_commit	—
`[1064f874abc0d05eeed8993815f584d847b72486,6e4012e571867868b545c91ca9d6095fdb709907)`	affected	code_commit	—
`[1064f874abc0d05eeed8993815f584d847b72486,d73f04e92c1aab78d96ac6cadb234c8a3a373d22)`	affected	code_commit	—
`[1064f874abc0d05eeed8993815f584d847b72486,18902a23ef36f83d32bafc58ae2484e6bb4bb8ef)`	affected	code_commit	—
`[1064f874abc0d05eeed8993815f584d847b72486,32bf92416614a1e3ff3524fc6b780259c7aad3ef)`	affected	code_commit	—
`5e6ef5ef6eaf690faad3a7c6c665ebf45d7b6ccf`	affected	code_commit	—
`839d42687dfce0ed0ea2c6bd8d707cc0e276fbe7`	affected	code_commit	—
`808e83e5add13152bd4a88346487de68395c136b`	affected	code_commit	—
`6de9d08a9718ee9c12ba6343c50141c2d633e3dc`	affected	code_commit	—
`[4.1.40,4.2)`	affected	generic	—
`[4.4.54,4.5)`	affected	generic	—
`[4.9.15,4.10)`	affected	generic	—
`[4.10.3,4.11)`	affected	generic	—

Linux

100%

Version	Status	Scheme	Platform
`4.11`	affected	generic	—
`[0,4.11)`	unaffected	generic	—
`[6.6.160,6.6.*]`	unaffected	generic	—
`[6.12.113,6.12.*]`	unaffected	generic	—
`[6.18.57,6.18.*]`	unaffected	generic	—
`[7.2.11,7.2.*]`	unaffected	generic	—
`[7.3,*]`	unaffected	generic	—

Linux

Linux Kernel

100%

Version	Status	Scheme	Platform
`[1064f874abc0d05eeed8993815f584d847b72486,f6394281834492c6516a405a348b545ae698a331)`	affected	code_commit	—
`[1064f874abc0d05eeed8993815f584d847b72486,6e4012e571867868b545c91ca9d6095fdb709907)`	affected	code_commit	—
`[1064f874abc0d05eeed8993815f584d847b72486,d73f04e92c1aab78d96ac6cadb234c8a3a373d22)`	affected	code_commit	—
`[1064f874abc0d05eeed8993815f584d847b72486,18902a23ef36f83d32bafc58ae2484e6bb4bb8ef)`	affected	code_commit	—
`[1064f874abc0d05eeed8993815f584d847b72486,32bf92416614a1e3ff3524fc6b780259c7aad3ef)`	affected	code_commit	—
`5e6ef5ef6eaf690faad3a7c6c665ebf45d7b6ccf`	affected	code_commit	—
`839d42687dfce0ed0ea2c6bd8d707cc0e276fbe7`	affected	code_commit	—
`808e83e5add13152bd4a88346487de68395c136b`	affected	code_commit	—
`6de9d08a9718ee9c12ba6343c50141c2d633e3dc`	affected	code_commit	—
`[4.1.40,4.2)`	affected	generic	—
`[4.4.54,4.5)`	affected	generic	—
`[4.9.15,4.10)`	affected	generic	—
`[4.10.3,4.11)`	affected	generic	—

Linux

Linux Kernel

100%

Version	Status	Scheme	Platform
`4.11`	affected	generic	—
`[0,4.11)`	unaffected	generic	—
`[6.6.160,6.6.*]`	unaffected	generic	—
`[6.12.113,6.12.*]`	unaffected	generic	—
`[6.18.57,6.18.*]`	unaffected	generic	—
`[7.2.11,7.2.*]`	unaffected	generic	—
`[7.3,*]`	unaffected	generic	—

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Remediation

No solution or workaround provided in the CVE record.

OpenCVE Recommended Actions

Upgrade the Linux kernel to a version that includes the commit fixing the race condition.
Avoid unmounting automounted NFS, AFS, CIFS, tracefs, or bind mounts with the MNT_SHRINKABLE flag when they may be in use; defer such operations until no active references exist.
Restrict unmount command privilege to trusted users or enforce stricter access controls in shared environments to reduce risk of accidental incorrect unmounting.

Generated by OpenCVE AI on October 29, 2026 at 23:01 UTC.

Tracking

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Advisories

No advisories yet.

No CVSS v4.0

Attack Vector Local

Attack Complexity High

Privileges Required High

Scope Unchanged

Confidentiality Impact None

Integrity Impact None

Availability Impact High

User Interaction None

No CVSS v3.0

No CVSS v2

This CVE is not in the KEV list.

The EPSS score is 0.00185.

Key SSVC decision points have not yet been added.

References

Link	Providers
https://git.kernel.org/pub/scm/linux/security/vulns.git/plain/cve/published/2026/CVE-2026-98990.mbox
https://git.kernel.org/stable/c/18902a23ef36f83d32bafc58ae2484e6bb4bb8ef
https://git.kernel.org/stable/c/32bf92416614a1e3ff3524fc6b780259c7aad3ef
https://git.kernel.org/stable/c/361f59e7f3f9a219fb5567bf9abc8482a154a399
https://git.kernel.org/stable/c/3f55f71291e4332983cd63b288d1f2be3c9c08fc
https://git.kernel.org/stable/c/6e4012e571867868b545c91ca9d6095fdb709907
https://git.kernel.org/stable/c/cda0c4e502a0f74a191471ce100fb061e5ab35d6
https://git.kernel.org/stable/c/d73f04e92c1aab78d96ac6cadb234c8a3a373d22
https://git.kernel.org/stable/c/f6394281834492c6516a405a348b545ae698a331
https://nvd.nist.gov/vuln/detail/CVE-2026-98990
https://www.cve.org/CVERecord?id=CVE-2026-98990

History

Fri, 30 Oct 2026 13:00:00 +0000

Type	Values Removed	Values Added
References		https://git.kernel.org/stable/c/361f59e7f3f9a219fb5567bf9abc8482a154a399 https://git.kernel.org/stable/c/3f55f71291e4332983cd63b288d1f2be3c9c08fc https://git.kernel.org/stable/c/cda0c4e502a0f74a191471ce100fb061e5ab35d6

Thu, 29 Oct 2026 20:00:00 +0000

Type	Values Removed	Values Added
Weaknesses	CWE-368

Thu, 29 Oct 2026 12:15:00 +0000

Type	Values Removed	Values Added
Weaknesses		CWE-826
References		https://git.kernel.org/pub/scm/linux/security/vulns.git/plain/cve/published/2026/CVE-2026-98990.mbox https://nvd.nist.gov/vuln/detail/CVE-2026-98990 https://www.cve.org/CVERecord?id=CVE-2026-98990
Metrics	threat_severity `None`	cvssV3_1 `{'score': 4.1, 'vector': 'CVSS:3.1/AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:H'}` threat_severity `Moderate`

Sat, 24 Oct 2026 01:15:00 +0000

Type	Values Removed	Values Added
First Time appeared		Linux linux
Vendors & Products		Linux linux

Fri, 23 Oct 2026 17:45:00 +0000

Type	Values Removed	Values Added
Weaknesses		CWE-368

Fri, 23 Oct 2026 12:45:00 +0000

Type	Values Removed	Values Added
Description		In the Linux kernel, the following vulnerability has been resolved: namespace: check a submount for references right before unmounting it shrink_submounts() and mark_mounts_for_expiry() first collect all the mounts they are allowed to unmount and then unmount them. Whether a mount is busy is decided by propagate_mount_busy() on the tree. But unmounting the first mount changes the tree that the second one propagates into. propagate_umount() moves a surviving overmount off a copy it unmounts and mounts it where the copy was mounted. If that's where the propagated copy of the second victim is looked up the overmount becomes a candidate of the second umount_tree(). It's childless and so trim_one() commits it without looking at its reference count. So a synchronous umount pulls out a busy mount that is in use somewhere else and marks it MNT_SYNC_UMOUNT while it has users: umount2(/tmp/plshrink/p1, 0) = 0 errno 0 cwd is (unreachable) The same two umounts requested one after the other fail with EBUSY. This needs a mount with MNT_SHRINKABLE, i.e., automounted submounts of NFS, AFS and CIFS or the tracefs mount below debugfs. Bind mounts inherit the flag. Check each mount right before it is unmounted under the same hold of namespace_sem and mount_lock as the umount itself. Make sure that the algorithm stays linear.
Title		namespace: check a submount for references right before unmounting it
First Time appeared		Linux Linux linux Kernel
CPEs		cpe:2.3:o:linux:linux_kernel::::::::
Vendors & Products		Linux Linux linux Kernel
References		https://git.kernel.org/stable/c/18902a23ef36f83d32bafc58ae2484e6bb4bb8ef https://git.kernel.org/stable/c/32bf92416614a1e3ff3524fc6b780259c7aad3ef https://git.kernel.org/stable/c/6e4012e571867868b545c91ca9d6095fdb709907 https://git.kernel.org/stable/c/d73f04e92c1aab78d96ac6cadb234c8a3a373d22 https://git.kernel.org/stable/c/f6394281834492c6516a405a348b545ae698a331

Subscriptions

Linux Linux Linux Kernel

MITRE

Status: PUBLISHED

Assigner: Linux

Published: 2026-10-23T12:20:09.349Z

Updated: 2026-10-30T12:40:44.542Z

Reserved: 2026-09-25T10:25:14.384Z

Link: CVE-2026-98990

Vulnrichment

No data.

NVD

Status : Received

Published: 2026-10-23T13:17:20.980

Modified: 2026-10-30T13:21:34.437

Link: CVE-2026-98990

Redhat

Severity : Moderate

Publid Date: 2026-10-23T00:00:00Z

Links: CVE-2026-98990 - Bugzilla

OpenCVE Enrichment

Updated: 2026-10-29T23:15:05Z

Weaknesses

CWE-826
Premature Release of Resource During Expected Lifetime

Impact

Affected Systems

Risk and Exploitability

Tracking

Attack Vector Local

Attack Complexity High

Privileges Required High

Scope Unchanged

Confidentiality Impact None

Integrity Impact None

Availability Impact High

User Interaction None

Subscriptions

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