CVE-2025-38247: userns and mnt_idmap leak in open_tree_attr(2)

Severity: medium (CVSS 5.5 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.1% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2025-07-09 · updated 2026-06-17

Description

In the Linux kernel, the following vulnerability has been resolved: userns and mnt_idmap leak in open_tree_attr(2) Once want_mount_setattr() has returned a positive, it does require finish_mount_kattr() to release ->mnt_userns. Failing do_mount_setattr() does not change that. As the result, we can end up leaking userns and possibly mnt_idmap as well.

Affected products

Linux kernel: from 6.15 before 6.15.5; 6.16-rc1, 6.16-rc2, 6.16-rc3 — fixed in 6.15.5

How to fix

Upgrade to a fixed version: Linux kernel 6.15.5. Check the vendor advisory for mitigations.

References

https://git.kernel.org/stable/c/0748e553df0225754c316a92af3a77fdc057b358
https://git.kernel.org/stable/c/142db4e76110dd80239f4e79810f85ea1735ad60

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