CVE-2025-39776: 
Linux Kernel vulnerability analysis and mitigation

CVE-2025-39776 is a vulnerability discovered in the Linux kernel's memory management subsystem, specifically in the mm/debugvmpgtable component. The vulnerability was disclosed on September 11, 2025, and affects systems running with CONFIGDEBUGVMPGTABLE=y enabled. The issue stems from improper handling of page table entries in the destroyargs() function (NVD, Red Hat).

The vulnerability occurs when the mm/debugvmpagetable test allocates manual page table entries for its tests using a manually allocated mmstruct. The critical flaw is in the destroyargs() function, which fails to properly clear these entries using the *_clear functions. This results in stale entries remaining in the system. The vulnerability has been assigned a CVSS v3.1 base score of 5.5 (AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H) (Red Hat).

When exploited, this vulnerability can lead to system instability when another process allocates an mmstruct with a pgd at the same address as a stale entry. This manifests as warnings and potential system errors, particularly in debug kernels with CONFIGDEBUGVMPGTABLE=y enabled (NVD).

Red Hat has marked this vulnerability as 'Fix deferred' for Red Hat Enterprise Linux 9 and 10, while versions 6, 7, and 8 are not affected. The fix involves properly clearing page table entries in the destroy_args() function (Red Hat).