Description
In the Linux kernel, the following vulnerability has been resolved:
namespace: keep the lock on a mount that a propagated copy is moved beneath
attach_recursive_mnt() transfers MNT_LOCKED from the top mount to the
mount that is moved beneath it with MOVE_MOUNT_BENEATH. This allows the
owner of a user namespace to replace its locked /proc or its root. The
mount beneath takes on the job of covering the underlying mountpoint
allowing the top mount to be unmounted.
Consider two mount namespaces:
(H) The host H has a shared mount P with a secret in P/d
(Z) Z is a user namespace made from M. Its copy of P receives
propagation from the host's P and its copy of M's cover on P/d is
locked Z's owner must not get to see P/d.
Now (H) mounts X on P/d. This propagates into (Z). The copy of X lands
beneath (Z)'s locked cover. The locked property is transfered from (Z)'s
cover to the copy of X propagated beneath it. The cover is now unlocked.
Now (H) unmounts X again. The copy of X in (Z) gets unmounted and the
covering mount is left unlocked on top of P/d. (Z) can now unmount it:
Z: umount2(P/d) = EINVAL /* the cover is locked */
H: mount X on P/d, umount X /* both propagate into Z /*
Z: umount2(P/d) = 0 /* the cover is now unlocked */
Z: read P/d/secret = "covered-by-root" /* secret revealed */
So only transfer the locked property to the mount beneath for mounts the
caller has placed. A propagated copy that lands beneath a locked mount
is locked as well so that the mount at the bottom of the stack carries a
lock the way every check expects. The mount on top of it remains locked
to ensure that it keeps covering even if the propagated mount is
unmounted again.
namespace: keep the lock on a mount that a propagated copy is moved beneath
attach_recursive_mnt() transfers MNT_LOCKED from the top mount to the
mount that is moved beneath it with MOVE_MOUNT_BENEATH. This allows the
owner of a user namespace to replace its locked /proc or its root. The
mount beneath takes on the job of covering the underlying mountpoint
allowing the top mount to be unmounted.
Consider two mount namespaces:
(H) The host H has a shared mount P with a secret in P/d
(Z) Z is a user namespace made from M. Its copy of P receives
propagation from the host's P and its copy of M's cover on P/d is
locked Z's owner must not get to see P/d.
Now (H) mounts X on P/d. This propagates into (Z). The copy of X lands
beneath (Z)'s locked cover. The locked property is transfered from (Z)'s
cover to the copy of X propagated beneath it. The cover is now unlocked.
Now (H) unmounts X again. The copy of X in (Z) gets unmounted and the
covering mount is left unlocked on top of P/d. (Z) can now unmount it:
Z: umount2(P/d) = EINVAL /* the cover is locked */
H: mount X on P/d, umount X /* both propagate into Z /*
Z: umount2(P/d) = 0 /* the cover is now unlocked */
Z: read P/d/secret = "covered-by-root" /* secret revealed */
So only transfer the locked property to the mount beneath for mounts the
caller has placed. A propagated copy that lands beneath a locked mount
is locked as well so that the mount at the bottom of the stack carries a
lock the way every check expects. The mount on top of it remains locked
to ensure that it keeps covering even if the propagated mount is
unmounted again.
Published:
2026-10-23
Score:
n/a
EPSS:
n/a
KEV:
No
Impact:
n/a
Action:
n/a
Analysis
No analysis available yet.
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 | Linux | unaffected |
|
|||||||||||||||
| Linux | Linux | affected |
|
No data.
No data.
No data available yet.
Remediation
No remediation available yet.
Tracking
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Advisories
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References
History
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: keep the lock on a mount that a propagated copy is moved beneath attach_recursive_mnt() transfers MNT_LOCKED from the top mount to the mount that is moved beneath it with MOVE_MOUNT_BENEATH. This allows the owner of a user namespace to replace its locked /proc or its root. The mount beneath takes on the job of covering the underlying mountpoint allowing the top mount to be unmounted. Consider two mount namespaces: (H) The host H has a shared mount P with a secret in P/d (Z) Z is a user namespace made from M. Its copy of P receives propagation from the host's P and its copy of M's cover on P/d is locked Z's owner must not get to see P/d. Now (H) mounts X on P/d. This propagates into (Z). The copy of X lands beneath (Z)'s locked cover. The locked property is transfered from (Z)'s cover to the copy of X propagated beneath it. The cover is now unlocked. Now (H) unmounts X again. The copy of X in (Z) gets unmounted and the covering mount is left unlocked on top of P/d. (Z) can now unmount it: Z: umount2(P/d) = EINVAL /* the cover is locked */ H: mount X on P/d, umount X /* both propagate into Z /* Z: umount2(P/d) = 0 /* the cover is now unlocked */ Z: read P/d/secret = "covered-by-root" /* secret revealed */ So only transfer the locked property to the mount beneath for mounts the caller has placed. A propagated copy that lands beneath a locked mount is locked as well so that the mount at the bottom of the stack carries a lock the way every check expects. The mount on top of it remains locked to ensure that it keeps covering even if the propagated mount is unmounted again. | |
| Title | namespace: keep the lock on a mount that a propagated copy is moved beneath | |
| First Time appeared |
Linux
Linux linux Kernel |
|
| CPEs | cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:* | |
| Vendors & Products |
Linux
Linux linux Kernel |
|
| References |
|
MITRE
Status: PUBLISHED
Assigner: Linux
Published:
Updated: 2026-10-23T12:19:49.363Z
Reserved: 2026-09-25T10:25:14.383Z
Link: CVE-2026-98976
Vulnrichment
No data.
NVD
No data.
Redhat
No data.
OpenCVE Enrichment
No data.
Weaknesses
No weakness.