CVE-2026-97943 x86/mm/pat: Acquire init_mm write lock on collapse to avoid UAF
A use-after-free in the Linux kernel x86/mm/pat component allows local attackers with high privileges to execute arbitrary code or escalate privileges.
- Exploited in the wild
- Not known
- Login needed
- An administrator
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-97943?
CVE-2026-97943 is an use after free vulnerability in Linux, published on 25 Sep 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:
x86/mm/pat: Acquire init_mm write lock on collapse to avoid UAF
x86 implements page attribute modification using its Change Page Attributes (CPA) mechanism.
This tracks properties of ranges such as cache mode through x86 page attributes, and as part of that logic manipulates kernel page tables.
Since commit:
41d88484c71c ("x86/mm/pat: restore large ROX pages after fragmentation")
ranges of kernel page table entries can be collapsed into huge page table entries as part of this logic.
As part of this collapse, it frees the page tables which the collapsed entries previously pointed to, and it does so without any relevant locks being held to preclude concurrent kernel page table walkers.
The only way this code can be reached is if CPA_COLLAPSE is specified, and this is only set in set_memory_rox() via:
set_memory_rox() -> change_page_attr_set_clr() -> cpa_flush() -> cpa_collapse_large_pages()
Notable users of this are execmem and BPF when manipulating executable mappings.
However, this is problematic for ptdump as it walks ranges it does not own and thus runs the risk of a use-after-free on page tables freed underneath it.
In addition, concurrent CPA collapse operations are possible which can also cause races.
Resolve the issue by acquiring the mmap write lock on init_mm across the whole operation.
It is safe to acquire a sleeping lock as all the callers invoke set_memory_rox() from process context and in any case, change_page_attr_set_clr() calls vm_unmap_alias() which ultimately takes a mutex, disallowing atomic context here.
Which versions are affected by CVE-2026-97943?
How do I fix CVE-2026-97943?
Apply the vendor's patch.
Upgrade to the fixed version. These bugs are found with fuzzing and sanitisers and avoided by memory-safe languages. More about Use after free.
Is CVE-2026-97943 being exploited?
There is no known exploitation of CVE-2026-97943 in the wild and no public exploit code.
Sources
Also known as BELL-CVE-2026-97943, DEBIAN-CVE-2026-97943, GHSA-vv3w-94g3-pv9v, UBUNTU-CVE-2026-97943.