CVE-2026-43472: Linux kernel · unshare: fix unshare_fs() handling
Affects Linux kernelSource CVE Database V5
Not known to be exploited · fixed in d7963d6997fea86a6def242ac36198b86655f912 : update Linux kernel when convenient.
Data as of 6 Nov 2026, 15:49 UTC
Rated by Threat Radar · No CVSS score from NVD or the CNA
Thin evidence
One scorer or none- CISA SSVC
- Exploitation
- No evidence of active exploitation and no public proof of concept
- Automatable
- Attackers cannot reliably automate steps 1–4 of the kill chain
- Technical impact
- Limited control over the software or limited information exposure
CISA SSVC assessment, 2026-11-06.
- Patch
- Available – fixed in d7963d6997fea86a6def242ac36198b86655f912, d3ffc8f13034af895531a02c30b1fe3a34b46432, d0d99f60538ddb4a62ccaac2168d8f448965f083 +5
Exploitation evidence
Disclosed: evidence found.
CVE published 8 May 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponized: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors
A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 6 Nov 2026.
What to do
Upgrade to a fixed release listed under Affected software.
Affected software
| Product | Affected | Fixed in |
|---|---|---|
| LinuxLinux | Affected
| Fixed in
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| LinuxLinux | Affected
| Fixed in
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| LinuxLinux | Affected
| Fixed in
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| LinuxLinux | Affected
| Fixed in
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| LinuxLinux | Affected
| Fixed in
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| LinuxLinux | Affected
| Fixed in
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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) ;-/
References
- git.kernel.org/stable/c/845bf3c6963a52096d0d3866e4a92db77a0c03d8 (opens in a new tab)
- git.kernel.org/stable/c/d3ffc8f13034af895531a02c30b1fe3a34b46432 (opens in a new tab)
- git.kernel.org/stable/c/d0d99f60538ddb4a62ccaac2168d8f448965f083 (opens in a new tab)
- git.kernel.org/stable/c/d7963d6997fea86a6def242ac36198b86655f912 (opens in a new tab)
- git.kernel.org/stable/c/aa9ebc084505fb26dd90f4d7a249045aad152043 (opens in a new tab)
- git.kernel.org/stable/c/af8f4be3b68ac8caa41c8e5ead0eeaf5e85e42d0 (opens in a new tab)
- git.kernel.org/stable/c/42e21e74061b0ebbd859839f81acf10efad02a27 (opens in a new tab)
- git.kernel.org/stable/c/6c4b2243cb6c0755159bd567130d5e12e7b10d9f (opens in a new tab)