CVE-2025-40105 vfs: Don't leak disconnected dentries on umount
A Linux kernel vulnerability allows attackers to cause a denial of service by triggering a memory leak that prevents unmounting filesystems.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2025-40105?
CVE-2025-40105 is a high-severity denial of service vulnerability in Linux, published on 30 Oct 2025. It can only be exploited from the same machine or local network, with no action from the victim.
Official description
In the Linux kernel, the following vulnerability has been resolved:
vfs: Don't leak disconnected dentries on umount
When user calls open_by_handle_at() on some inode that is not cached, we will create disconnected dentry for it. If such dentry is a directory, exportfs_decode_fh_raw() will then try to connect this dentry to the dentry tree through reconnect_path(). It may happen for various reasons (such as corrupted fs or race with rename) that the call to lookup_one_unlocked() in reconnect_one() will fail to find the dentry we are trying to reconnect and instead create a new dentry under the parent. Now this dentry will not be marked as disconnected although the parent still may well be disconnected (at least in case this inconsistency happened because the fs is corrupted and .. doesn't point to the real parent directory). This creates inconsistency in disconnected flags but AFAICS it was mostly harmless. At least until commit f1ee616214cb ("VFS: don't keep disconnected dentries on d_anon") which removed adding of most disconnected dentries to sb->s_anon list. Thus after this commit cleanup of disconnected dentries implicitely relies on the fact that dput() will immediately reclaim such dentries. However when some leaf dentry isn't marked as disconnected, as in the scenario described above, the reclaim doesn't happen and the dentries are "leaked". Memory reclaim can eventually reclaim them but otherwise they stay in memory and if umount comes first, we hit infamous "Busy inodes after unmount" bug. Make sure all dentries created under a disconnected parent are marked as disconnected as well.
Which versions are affected by CVE-2025-40105?
How do I fix CVE-2025-40105?
Apply the vendor's patch.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2025-40105 being exploited?
There is no known exploitation of CVE-2025-40105 in the wild and no public exploit code.
Sources
Also known as AZL-69421, BELL-CVE-2025-40105, DEBIAN-CVE-2025-40105, GHSA-9wgm-cmcc-8467, ROOT-OS-DEBIAN-11-CVE-2025-40105, ROOT-OS-DEBIAN-12-CVE-2025-40105 and 4 more.