CVE-2025-40270 mm, swap: fix potential UAF issue for VMA readahead
A race condition in Linux kernel swap VMA readahead can cause a use-after-free, potentially allowing local attackers to execute code or escalate privileges.
- 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-2025-40270?
CVE-2025-40270 is a high-severity use after free vulnerability in Linux, published on 6 Dec 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, swap: fix potential UAF issue for VMA readahead
Since commit 78524b05f1a3 ("mm, swap: avoid redundant swap device pinning"), the common helper for allocating and preparing a folio in the swap cache layer no longer tries to get a swap device reference internally, because all callers of __read_swap_cache_async are already holding a swap entry reference. The repeated swap device pinning isn't needed on the same swap device.
Caller of VMA readahead is also holding a reference to the target entry's swap device, but VMA readahead walks the page table, so it might encounter swap entries from other devices, and call __read_swap_cache_async on another device without holding a reference to it.
So it is possible to cause a UAF when swapoff of device A raced with swapin on device B, and VMA readahead tries to read swap entries from device A. It's not easy to trigger, but in theory, it could cause real issues.
Make VMA readahead try to get the device reference first if the swap device is a different one from the target entry.
Which versions are affected by CVE-2025-40270?
How do I fix CVE-2025-40270?
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-2025-40270 being exploited?
There is no known exploitation of CVE-2025-40270 in the wild and no public exploit code.
Sources
Also known as BELL-CVE-2025-40270, DEBIAN-CVE-2025-40270, GHSA-hfc9-3847-7v4r, UBUNTU-CVE-2025-40270.