CVE-2025-22036 is a vulnerability identified in the Linux kernel's exFAT filesystem driver, specifically related to the handling of buffer_head structures on the stack during block read operations. The flaw arises when the function get_block is called with a buffer_head allocated on the stack, such as in the do_mpage_readpage function. Under certain race conditions involving concurrent CPU operations, this can lead to use-after-free (UAF) scenarios where the buffer_head reference count is decremented prematurely, causing random stack corruption. The vulnerability is triggered when one CPU thread is executing mpage_read_folio and its associated functions, while another CPU thread concurrently manipulates the buffer_head reference count, leading to the buffer_head becoming invalid while still in use. The patch for this vulnerability changes the behavior of bh_read to return -EAGAIN if the folio lacks buffers, prompting the caller to fallback to safer functions like block_read_full_folio that create a buffer_head in the folio before retrying get_block. This prevents calling bh_read with an on-stack buffer_head, thereby avoiding the race condition and stack corruption. This vulnerability affects Linux kernel versions identified by the commit hash 11a347fb6cef62ce47e84b97c45f2b2497c7593b and was published on April 16, 2025. There are no known exploits in the wild at this time, and no CVSS score has been assigned yet.

For European organizations, this vulnerability poses a risk primarily to systems running Linux kernels with the affected exFAT driver code, especially those handling exFAT-formatted storage devices. The exFAT filesystem is commonly used for removable storage media such as USB drives and SD cards, which are frequently used in enterprise environments for data transfer and backup. Exploitation of this vulnerability could lead to stack corruption, potentially allowing local attackers or malicious processes to cause system instability, crashes (denial of service), or in worst cases, arbitrary code execution with kernel privileges. This could compromise the confidentiality, integrity, and availability of affected systems. Given the widespread use of Linux in European data centers, cloud infrastructure, and embedded systems, the vulnerability could impact critical infrastructure, enterprise servers, and endpoint devices. The lack of known exploits currently reduces immediate risk, but the complexity of the race condition and kernel-level impact means that once exploited, the consequences could be severe. Organizations relying on Linux systems that mount exFAT filesystems should consider the risk of local privilege escalation or denial of service attacks, especially in multi-tenant or shared environments.

European organizations should prioritize updating their Linux kernels to versions that include the patch for CVE-2025-22036 as soon as vendor updates become available. Until patches are applied, organizations should consider the following mitigations: 1) Limit or restrict the use of exFAT-formatted removable media on critical systems, or enforce strict scanning and validation of such media before use. 2) Employ kernel hardening techniques such as Kernel Address Space Layout Randomization (KASLR), stack canaries, and control flow integrity to reduce the impact of potential exploitation. 3) Monitor system logs and kernel messages for unusual buffer_head or filesystem-related errors that might indicate exploitation attempts. 4) Use mandatory access controls (e.g., SELinux, AppArmor) to restrict the ability of untrusted users or processes to mount or access exFAT filesystems. 5) In environments where kernel updates are delayed, consider disabling exFAT support if not required, or mounting exFAT devices in user space via FUSE-based drivers as a temporary workaround. 6) Conduct thorough testing of kernel updates in staging environments to ensure stability and compatibility before production deployment.