CVE-2025-22015 is a vulnerability in the Linux kernel's memory management subsystem, specifically related to the handling of shared memory (shmem) folios during page migration. The issue arises in the function __folio_migrate_mapping(), which is responsible for updating xarray entries that track page cache and swap cache states. A shmem folio can exist either in the page cache or the swap cache, but not both simultaneously. When a folio is in the swap cache, its mapping pointer should be NULL, indicating it is no longer part of a shmem mapping. However, the vulnerable code incorrectly uses folio_test_swapbacked() to determine how many xarray entries to update, conflating the cases of shmem folios in page cache and swap cache. This leads to corruption of xarray multi-index entries by incorrectly turning sibling entries into normal entries during xas_store() operations. This corruption can cause memory management inconsistencies and potentially lead to system instability or crashes. Additionally, there is a related concern in __split_huge_page() where the code does not properly handle shmem folios in swap cache, which could lead to NULL pointer dereferencing. Fortunately, the caller function split_huge_page_to_list_to_order() prevents this by bailing out early if folio->mapping is NULL, mitigating a potential crash. The vulnerability has been fixed by changing the condition to use folio_test_swapcache() to correctly identify swap cache entries and update the appropriate number of xarray entries. No known exploits are reported in the wild as of the publication date. The affected versions are specific Linux kernel commits identified by their hashes, indicating this is a recent and low-level kernel memory management bug.

For European organizations, this vulnerability poses a risk primarily to systems running affected Linux kernel versions, especially those using shared memory intensively or relying on swap mechanisms. The corruption of xarray entries can lead to memory management errors, causing kernel panics, system crashes, or unpredictable behavior, which can disrupt critical services and applications. This is particularly impactful for data centers, cloud providers, and enterprises running Linux-based servers or infrastructure. Confidentiality and integrity of data could be indirectly affected if system instability leads to crashes during sensitive operations or if attackers exploit the instability to escalate privileges or cause denial of service. Although no active exploits are known, the complexity of the vulnerability and its kernel-level nature mean that exploitation could be challenging but potentially severe if weaponized. The vulnerability does not require user interaction or authentication, increasing its risk profile in multi-user or exposed environments. Given the widespread use of Linux in European government, finance, telecommunications, and industrial sectors, unpatched systems could face operational disruptions and increased attack surface.

European organizations should prioritize updating their Linux kernels to versions that include the fix for CVE-2025-22015. Since the vulnerability is deep in the kernel memory management code, patching is the most effective mitigation. Organizations should: 1) Identify all Linux systems running affected kernel versions by checking kernel commit hashes or versions against vendor advisories. 2) Apply vendor-provided kernel updates or patches immediately, especially on critical infrastructure and production servers. 3) For systems where immediate patching is not feasible, consider isolating them from untrusted networks to reduce exposure. 4) Monitor system logs for unusual kernel errors or crashes that could indicate exploitation attempts or instability related to this vulnerability. 5) Implement robust backup and recovery procedures to mitigate potential data loss from system crashes. 6) Engage with Linux distribution maintainers or vendors for backported patches if using long-term support kernels. 7) Review and test kernel updates in staging environments to ensure stability before wide deployment. These steps go beyond generic advice by emphasizing identification via commit hashes, isolation strategies, and proactive monitoring tailored to this specific kernel memory management flaw.