CVE-2025-21836 io_uring/kbuf: reallocate buf lists on upgrade
A use-after-free vulnerability in the Linux kernel's io_uring subsystem allows local attackers to potentially execute arbitrary 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-2025-21836?
CVE-2025-21836 is a high-severity use after free vulnerability in Linux kernel, published on 7 Mar 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/kbuf: reallocate buf lists on upgrade
IORING_REGISTER_PBUF_RING can reuse an old struct io_buffer_list if it was created for legacy selected buffer and has been emptied. It violates the requirement that most of the field should stay stable after publish. Always reallocate it instead.
Which versions are affected by CVE-2025-21836?
It affects 1 product.
Products include Linux kernel.
How do I fix CVE-2025-21836?
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-2025-21836 being exploited?
There is no known exploitation of CVE-2025-21836 in the wild and no public exploit code.
Other vulnerabilities in Linux kernel
Sources
Also known as BELL-CVE-2025-21836, DEBIAN-CVE-2025-21836, GHSA-wh23-v966-32jj, ROOT-OS-DEBIAN-12-CVE-2025-21836, ROOT-OS-UBUNTU-2404-CVE-2025-21836, UBUNTU-CVE-2025-21836.