Medium [CVE-2026-72034] reject detached mounts in capable_wrt_mount
This medium-severity Red Hat Linux advisory covers CVE-2026-72034 affecting Red Hat Enterprise Linux 10, Red Hat Enterprise Linux 9, Red Hat package: kernel-rt.
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Summary
In the Linux kernel, the following vulnerability has been resolved: fhandle: reject detached mounts in capable_wrt_mount() The recent fhandle RCU fix moved the mount namespace capability check into capable_wrt_mount(), so a non-NULL mnt_namespace survives the ns_capable() dereference.
The helper still assumes the later READ_ONCE(mount->mnt_ns) must be non-NULL because may_decode_fh() checked is_mounted() first. That assumption is not stable.
A detached mount from open_tree(..., OPEN_TREE_CLONE) can be dissolved on fput while open_by_handle_at() is between those checks, and umount_tree() can clear mount->mnt_ns. If the helper observes NULL, it dereferences mnt_ns->user_ns and panics.
Return false when the RCU read observes a detached mount. This keeps the relaxed permission path conservative: a mount no longer attached to a namespace cannot authorize open_by_handle_at() access.
A flaw was found in the Linux kernel's file handle (fhandle) mechanism. A local attacker could exploit a vulnerability in the capable_wrt_mount() function, which incorrectly handles detached mounts.
By performing specific operations, an attacker could trigger a null pointer dereference, leading to a system panic and causing a Denial of Service (DoS) on the affected system. Red Hat severity: Moderate — CVSS 5.5 (CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H).
Weakness: CWE-476.
Affected versions
No affected-version range was extracted from the source record. The vendor advisory is authoritative — check it before change work.
Official advisory · medium-confidence parse· fetched 26 days ago·verify at source
Fixed versions
No fixed release is recorded yet. That does not prove no patch exists — confirm against the vendor advisory.
Official advisory · medium-confidence parse· fetched 26 days ago·verify at source
Mitigation
The source record does not include mitigation steps. That is not a statement that no fix exists — read the vendor advisory below for the authoritative guidance.
Official advisory · medium-confidence parse· fetched 26 days ago·verify at source
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