CVE-2026-43472
Analyzed
Analyzed - Analysis Complete
Linux Kernel Unshare Filesystem Handling Vulnerability
Publication date: 2026-05-08
Last updated on: 2026-05-21
Assigner: kernel.org
Description
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) ;-/
CVSS Scores
EPSS Scores
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Meta Information
Affected Vendors & Products
| Vendor | Product | Version / Range |
|---|---|---|
| linux | linux_kernel | 2.6.16 |
| linux | linux_kernel | 2.6.16 |
| linux | linux_kernel | 2.6.16 |
| linux | linux_kernel | 2.6.16 |
| linux | linux_kernel | 2.6.16 |
| linux | linux_kernel | 2.6.16 |
| linux | linux_kernel | 7.0 |
| linux | linux_kernel | From 6.2 (inc) to 6.6.130 (exc) |
| linux | linux_kernel | From 5.11 (inc) to 5.15.203 (exc) |
| linux | linux_kernel | From 5.16 (inc) to 6.1.167 (exc) |
| linux | linux_kernel | From 6.13 (inc) to 6.18.19 (exc) |
| linux | linux_kernel | From 6.7 (inc) to 6.12.78 (exc) |
| linux | linux_kernel | From 6.19 (inc) to 6.19.9 (exc) |
| linux | linux_kernel | From 2.6.16.1 (inc) to 5.10.253 (exc) |
Helpful Resources
Exploitability
CWE
KEV
| CWE ID | Description |
|---|---|
| CWE-908 | The product uses or accesses a resource that has not been initialized. |
