CVE-2025-38499: clone_private_mnt(): make sure that caller has CAP_SYS_ADMIN in the right userns

Severity: medium (CVSS 5.5 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.2% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2025-08-11 · updated 2026-10-15

Description

In the Linux kernel, the following vulnerability has been resolved: clone_private_mnt(): make sure that caller has CAP_SYS_ADMIN in the right userns What we want is to verify there is that clone won't expose something hidden by a mount we wouldn't be able to undo. "Wouldn't be able to undo" may be a result of MNT_LOCKED on a child, but it may also come from lacking admin rights in the userns of the namespace mount belongs to. clone_private_mnt() checks the former, but not the latter. There's a number of rather confusing CAP_SYS_ADMIN checks in various userns during the mount, especially with the new mount API; they serve different purposes and in case of clone_private_mnt() they usually, but not always end up covering the missing check mentioned above.

Affected products

Debian Linux: 11.0
Linux kernel: from 4.4.281 before 4.5; from 4.9.280 before 4.10; from 4.14.244 before 4.15; from 4.19.204 before 4.20; from 5.4.141 before 5.5; from 5.10.59 before 5.11 — fixed in 4.10, 4.15, 4.20, 4.5, 5.11, 5.14

How to fix

Upgrade to a fixed version: Linux kernel 4.10, 4.15, 4.20, 4.5. Check the vendor advisory for mitigations.

References

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