CVE-2025-39793 io_uring/memmap: cast nr_pages to size_t before shifting
A missing cast in Linux kernel io_uring memory mapping allows integer overflow when root bypasses memory accounting, potentially enabling privilege escalation or code execution.
- 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-2025-39793?
CVE-2025-39793 is a high-severity vulnerability in Linux kernel, published on 12 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:
io_uring/memmap: cast nr_pages to size_t before shifting
If the allocated size exceeds UINT_MAX, then it's necessary to cast the mr->nr_pages value to size_t to prevent it from overflowing. In practice this isn't much of a concern as the required memory size will have been validated upfront, and accounted to the user. And > 4GB sizes will be necessary to make the lack of a cast a problem, which greatly exceeds normal user locked_vm settings that are generally in the kb to mb range. However, if root is used, then accounting isn't done, and then it's possible to hit this issue.
Which versions are affected by CVE-2025-39793?
It affects 1 product.
Products include Linux kernel.
How do I fix CVE-2025-39793?
Apply the vendor's patch.
Is CVE-2025-39793 being exploited?
There is no known exploitation of CVE-2025-39793 in the wild and no public exploit code.
Other vulnerabilities in Linux kernel
Sources
Also known as BELL-CVE-2025-39793, DEBIAN-CVE-2025-39793, GHSA-53xm-w39p-m328, UBUNTU-CVE-2025-39793.