namespace: don't inherit MNT_UMOUNT in clone_mnt()
- Published
- Last modified
- Where the record stands: published, rejected by its publisher, or superseded by another id.What do these mean? →
- published
- Whether CISA lists it in its Known Exploited Vulnerabilities catalog: proof that attackers are using it.What do these mean? →
- Not listed in CISA KEV
- How many real-world setups can hit the bug, from the vendor's advisory and CISA data. It does not know your setup.What do these mean? →
- Specific setups only
- Fix
- Fixed in 4.1, 6.6.160, 6.12.114, 6.18.57, 7.2.11
- Whether working attack code is public (Exploit-DB, Metasploit, Nuclei or GitHub). Public code makes attacks easier.What do these mean? →
- None on Exploit-DB, Metasploit or GitHub
Summary
In the Linux kernel, the following vulnerability has been resolved: namespace: don't inherit MNT_UMOUNT in clone_mnt() MNT_UMOUNT gets raised on a mount that umount_tree() or umount_one() has taken out of its namespace. It's never cleared. __detach_mounts() unhooks a mount that carries it instead of unmounting it. disconnect_mount() lets an unmounted child stay attached only if its parent carries it. propagate_umount() takes it as the sign that a mount is going to be unmounted when it decides what else can be unmounted, where a chain of locked mounts ends and where a for reparenting an overmount. clone_mnt() copies the flags of the source and only masks MNT_INTERNAL_FLAGS which doesn't include MNT_UMOUNT. A mount that was lazily unmounted but is kept alive by a file descriptor can still be copied when its root is an nsfs or pidfs file because may_copy_tree() accepts those before checking whether the source is mounted at all: mount --bind /proc/self/ns/net /tmp/x exec 3< /tmp/x umount -l /tmp/x mount --bind /proc/self/fd/3 /tmp/y The mount on /tmp/y is attached to the caller's namespace with MNT_UMOUNT already set and every copy of it inherits the flag again. That causes a number of bugs: • Unlink its mountpoint from a mount namespace where it isn't one. __detach_mounts() takes it for a mount that was unmounted earlier, unhooks it from its parent and drops the reference the namespace holds on it. It stays in the namespace with one reference too few and as its own parent, so it can't be unmounted through the file descriptor anymore and the namespace never finds it again. When the namespace goes away it's leaked and points to a freed struct mnt_namespace that may_change_propagation() and anon_ns_root() read on the next propagation change or mount_setattr() through the file descriptor. • Make it shared and unmount a peer. trace_transfers() follows the flag from the peer into it and strips it from its peer group. • Let a propagated umount reach it. gather_candidates() marks it with T_UMOUNT_CANDIDATE but never puts it on the candidate list, so the mark is never cleared and every later propagated umount skips it. If it's the parent of a locked mount handle_locked() takes it as the cutoff and commits the locked child that should have stayed and disconnect_mount() leaves that child attached to it, unmounted under a mounted parent, which is what disconnect_mount() exists to prevent. When the namespace goes away umount_tree() visits the child a second time. And once __detach_mounts() has made it its own parent reparent() never finds the end of the chain of unmounted parents. A clone is a new mount that has never been unmounted. Add MNT_UMOUNT to MNT_INTERNAL_FLAGS so clone_mnt() never copies it. And warn when umount_tree() reaches a mount that already has it set.
Timeline
- CVE published
- First seen by cve.now
- Record last updated
Affected versions
- Linux Linux
From 4.0.2 · fixed in 4.1
- Linux Linux
4.1
- KernelLinux
From 4.1.0 · fixed in 6.6.160; From 6.7.0 · fixed in 6.12.114; From 6.13.0 · fixed in 6.18.57; From 6.19.0 · fixed in 7.2.11
References 8
git.kernel.org
- stable/c/b201d59d047a5e05728c10864a56bdb67950d0b1
- stable/c/de098fb4594f8724fa286f08c7f42837bc19b478
- stable/c/fc1f3a476c35164c1beed7090fc0e630f52d778e
- stable/c/99698cfa34e493fc091219056aae446fe9442a96
- stable/c/c26c1a91ad2881a194f7af543e0b57f0870006b2
- stable/c/eecc9cd0fc07dba3f7fb0b2f844b4029435a2f7b
- stable/c/5077b52e9e4d72da53c50251296b99cd416765a1
- stable/c/e2c6d326216642011da318b9edfd5d57ebd5a56f
Questions about CVE-2026-98993
What does this mean?
A mount that was lazily unmounted but is kept alive by a file descriptor can be copied with a bind mount when the descriptor refers to an nsfs or pidfs file. The kernel then mishandles the mount's namespace references, so a mount can be unlinked from a namespace it is not in, the namespace can be leaked and point to freed memory, a peer mount can be unmounted, and propagated umounts can reach mounts they should not.Source: git.kernel.org
Am I affected, and how do I check?
The listed Linux kernel ranges are 4.1.0 up to 6.6.160, 6.7.0 up to 6.12.114, 6.13.0 up to 6.18.57, and 6.19.0 up to 7.2.11. The bug needs a lazily unmounted mount kept alive by an nsfs or pidfs file descriptor. To check a kernel version, run uname -r.Source: git.kernel.org
What should I do about it?
Move to the fixed release for the kernel branch in use: 6.6.160, 6.12.114, 6.18.57, or 7.2.11. The facts do not name a fix for every listed range, so check the kernel vendor's stable release notes for the matching branch.Source: git.kernel.org
Is it being exploited?
It is not in CISA's Known Exploited Vulnerabilities catalog, and CISA's SSVC assessment does not mark exploitation as active. That does not mean it has not been attacked: vendors and researchers can report attacks before CISA lists them. No public exploit code is tracked.Source: cve.now feed data