CVE-2025-39717 open_tree_attr: do not allow id-mapping changes without OPEN_TREE_CLONE
A Linux kernel bug allows changing id-mappings on detached mounts, potentially leading to use-after-free and privilege escalation.
- 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-2025-39717?
CVE-2025-39717 is a high-severity use after free 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:
open_tree_attr: do not allow id-mapping changes without OPEN_TREE_CLONE
As described in commit 7a54947e727b ('Merge patch series "fs: allow changing idmappings"'), open_tree_attr(2) was necessary in order to allow for a detached mount to be created and have its idmappings changed without the risk of any racing threads operating on it. For this reason, mount_setattr(2) still does not allow for id-mappings to be changed.
However, there was a bug in commit 2462651ffa76 ("fs: allow changing idmappings") which allowed users to bypass this restriction by calling open_tree_attr(2) *without* OPEN_TREE_CLONE.
can_idmap_mount() prevented this bug from allowing an attached mountpoint's id-mapping from being modified (thanks to an is_anon_ns() check), but this still allows for detached (but visible) mounts to have their be id-mapping changed. This risks the same UAF and locking issues as described in the merge commit, and was likely unintentional.
Weakness: CWE-416
Which versions are affected by CVE-2025-39717?
It affects 1 product.
Products include Linux kernel.
How do I fix CVE-2025-39717?
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-2025-39717 being exploited?
There is no known exploitation of CVE-2025-39717 in the wild and no public exploit code.
Other vulnerabilities in Linux kernel
Sources
Also known as BELL-CVE-2025-39717, DEBIAN-CVE-2025-39717, GHSA-48pq-57c2-69ww, UBUNTU-CVE-2025-39717.