CVE-2025-21709 kernel: be more careful about dup_mmap() failures and uprobe registering
A race condition in the Linux kernel's memory management can lead to system instability or crashes when memory allocation fails during process forking.
- 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-2025-21709?
CVE-2025-21709 is a high-severity vulnerability in Linux kernel, published on 27 Feb 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:
kernel: be more careful about dup_mmap() failures and uprobe registering
If a memory allocation fails during dup_mmap(), the maple tree can be left in an unsafe state for other iterators besides the exit path. All the locks are dropped before the exit_mmap() call (in mm/mmap.c), but the incomplete mm_struct can be reached through (at least) the rmap finding the vmas which have a pointer back to the mm_struct.
Up to this point, there have been no issues with being able to find an mm_struct that was only partially initialised. Syzbot was able to make the incomplete mm_struct fail with recent forking changes, so it has been proven unsafe to use the mm_struct that hasn't been initialised, as referenced in the link below.
Although 8ac662f5da19f ("fork: avoid inappropriate uprobe access to invalid mm") fixed the uprobe access, it does not completely remove the race.
This patch sets the MMF_OOM_SKIP to avoid the iteration of the vmas on the oom side (even though this is extremely unlikely to be selected as an oom victim in the race window), and sets MMF_UNSTABLE to avoid other potential users from using a partially initialised mm_struct.
When registering vmas for uprobe, skip the vmas in an mm that is marked unstable. Modifying a vma in an unstable mm may cause issues if the mm isn't fully initialised.
Which versions are affected by CVE-2025-21709?
It affects 1 product.
Products include Linux kernel.
How do I fix CVE-2025-21709?
Apply the vendor's patch.
Is CVE-2025-21709 being exploited?
There is no known exploitation of CVE-2025-21709 in the wild and no public exploit code.
Other vulnerabilities in Linux kernel
Sources
Also known as BELL-CVE-2025-21709, DEBIAN-CVE-2025-21709, GHSA-vh2p-4gfm-v9v7, ROOT-OS-DEBIAN-13-CVE-2025-21709, ROOT-OS-UBUNTU-2404-CVE-2025-21709, UBUNTU-CVE-2025-21709.