CVE-2025-39717

/// Technical 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

/// Remediation

Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

/// References