CVE-2025-39725 mm/vmscan: fix hwpoisoned large folio handling in shrink_folio_list
A race condition in Linux kernel memory reclaim causes a null pointer dereference and kernel panic when handling hwpoisoned large folios.
- 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-2025-39725?
CVE-2025-39725 is a medium-severity vulnerability in Linux kernel, published on 5 Sep 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:
mm/vmscan: fix hwpoisoned large folio handling in shrink_folio_list
In shrink_folio_list(), the hwpoisoned folio may be large folio, which can't be handled by unmap_poisoned_folio(). For THP, try_to_unmap_one() must be passed with TTU_SPLIT_HUGE_PMD to split huge PMD first and then retry. Without TTU_SPLIT_HUGE_PMD, we will trigger null-ptr deref of pvmw.pte. Even we passed TTU_SPLIT_HUGE_PMD, we will trigger a WARN_ON_ONCE due to the page isn't in swapcache.
Since UCE is rare in real world, and race with reclaimation is more rare, just skipping the hwpoisoned large folio is enough. memory_failure() will handle it if the UCE is triggered again.
This happens when memory reclaim for large folio races with memory_failure(), and will lead to kernel panic. The race is as follows:
cpu0 cpu1 shrink_folio_list memory_failure TestSetPageHWPoison unmap_poisoned_folio --> trigger BUG_ON due to unmap_poisoned_folio couldn't handle large folio
[[email protected]: add comment to unmap_poisoned_folio()]
Weakness: CWE-476
Which versions are affected by CVE-2025-39725?
It affects 1 product.
Products include Linux kernel.
How do I fix CVE-2025-39725?
Apply the vendor's patch.
Is CVE-2025-39725 being exploited?
There is no known exploitation of CVE-2025-39725 in the wild and no public exploit code.
Other vulnerabilities in Linux kernel
Sources
Also known as BELL-CVE-2025-39725, DEBIAN-CVE-2025-39725, GHSA-qmpx-wcm9-r94f, UBUNTU-CVE-2025-39725.