CVE-2026-72173

A flaw was found in the Linux kernel's memory management unit (MMU). The pagemap_pmd_range_thp() function incorrectly issued a warning when encountering certain non-present Page Middle Directory (PMD) entries. This issue arose because an assertion related to migration-only softleaf entries became outdated after the introduction of device-private PMD entries. While not directly exploitable for arbitrary code execution or privilege escalation, this flaw could lead to misleading diagnostic information within the kernel.

A low impact flaw was found in the Linux kernel's memory management code in fs/proc/task_mmu.c. The pagemap_pmd_range_thp() function contained a stale warning that fired whenever it encountered a non-present Page Middle Directory (PMD) entry that was not a migration entry; this assertion became outdated once device-private PMD entries (used with HMM/device memory) were introduced. A local user able to inspect the pagemap of a process whose address space contains such device-private PMD mappings could trigger this kernel warning, producing misleading diagnostic output, and on systems configured with panic_on_warn it could turn into a kernel panic (denial of service). No use-after-free, out-of-bounds access, or privilege escalation is indicated. Red Hat Enterprise Linux 7, 8, 9, and 10 (including the kernel-rt variants) and Red Hat In-Vehicle OS are not affected because the vulnerable code is not present in those releases; the Red Hat Enterprise Linux 6 Extended Lifecycle Support stream is out of support scope. Red Hat assesses the impact of this flaw as Low, which is lower than the Moderate severity implied by the CVSS:3.1 vector AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H, because the issue is warning-driven, requires the presence of device-private PMD mappings, and does not affect confidentiality or integrity.

The CVSS score(s) listed for this vulnerability do not reflect the associated product's status, and are included for informational purposes to better understand the severity of this vulnerability.

Mitigation for this issue is either not available or the currently available options do not meet the Red Hat Product Security criteria comprising ease of use and deployment, applicability to widespread installation base, or stability.