CVE-2026-43472 unshare: fix unshare_fs() handling
A race condition in Linux kernel unshare() can leave processes with detached mounts, causing denial of service.
- 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-2026-43472?
CVE-2026-43472 is a medium-severity vulnerability in Linux kernel, published on 8 May 2026. 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:
unshare: fix unshare_fs() handling
There's an unpleasant corner case in unshare(2), when we have a CLONE_NEWNS in flags and current->fs hadn't been shared at all; in that case copy_mnt_ns() gets passed current->fs instead of a private copy, which causes interesting warts in proof of correctness]
> I guess if private means fs->users == 1, the condition could still be true.
Unfortunately, it's worse than just a convoluted proof of correctness. Consider the case when we have CLONE_NEWCGROUP in addition to CLONE_NEWNS (and current->fs->users == 1).
We pass current->fs to copy_mnt_ns(), all right. Suppose it succeeds and flips current->fs->{pwd,root} to corresponding locations in the new namespace. Now we proceed to copy_cgroup_ns(), which fails (e.g. with -ENOMEM). We call put_mnt_ns() on the namespace created by copy_mnt_ns(), it's destroyed and its mount tree is dissolved, but... current->fs->root and current->fs->pwd are both left pointing to now detached mounts.
They are pinning those, so it's not a UAF, but it leaves the calling process with unshare(2) failing with -ENOMEM _and_ leaving it with pwd and root on detached isolated mounts. The last part is clearly a bug.
There is other fun related to that mess (races with pivot_root(), including the one between pivot_root() and fork(), of all things), but this one is easy to isolate and fix - treat CLONE_NEWNS as "allocate a new fs_struct even if it hadn't been shared in the first place". Sure, we could go for something like "if both CLONE_NEWNS *and* one of the things that might end up failing after copy_mnt_ns() call in create_new_namespaces() are set, force allocation of new fs_struct", but let's keep it simple - the cost of copy_fs_struct() is trivial.
Another benefit is that copy_mnt_ns() with CLONE_NEWNS *always* gets a freshly allocated fs_struct, yet to be attached to anything. That seriously simplifies the analysis...
FWIW, that bug had been there since the introduction of unshare(2) ;-/
Weakness: CWE-908
Which versions are affected by CVE-2026-43472?
It affects 1 product.
Products include Linux kernel.
How do I fix CVE-2026-43472?
Apply the vendor's patch.
Is CVE-2026-43472 being exploited?
There is no known exploitation of CVE-2026-43472 in the wild and no public exploit code.
Other vulnerabilities in Linux kernel
Sources
Also known as BELL-CVE-2026-43472, DEBIAN-CVE-2026-43472, GHSA-vgv8-2mh4-qh7r, ROOT-OS-DEBIAN-11-CVE-2026-43472, ROOT-OS-UBUNTU-2204-CVE-2026-43472, ROOT-OS-UBUNTU-2404-CVE-2026-43472 and 1 more.