CVE-2024-39371 is a vulnerability identified in the Linux kernel's io_uring subsystem, specifically related to the function io_file_can_poll(). The vulnerability arises from a missing check for a non-NULL file pointer during the forced asynchronous (async) preparation path. In earlier kernel versions, if an io_uring request was marked as forced async but had no valid file descriptor assigned (i.e., a NULL file pointer), it could trigger a NULL pointer dereference. This results in a kernel oops (crash) due to an invalid memory access at address 0x00000000000000b0. The vulnerability is triggered when the kernel attempts to select an I/O buffer via io_buffer_select() without verifying the validity of the file pointer, leading to a page fault and kernel panic. The trace provided shows the call stack leading to the crash, indicating that the issue occurs during the asynchronous I/O submission process (io_submit_sqes and related functions). The root cause is that the forced async preparation path does not adequately validate the file descriptor before proceeding, allowing a NULL pointer dereference. The fix involves adding a safety check in io_file_can_poll() to ensure the file pointer is not NULL before proceeding. This prevents the kernel from dereferencing a NULL pointer and instead results in a controlled error response (CQE posted with -EBADF), indicating a bad file descriptor. The vulnerability affects Linux kernel versions prior to the patch and is relevant to systems using io_uring for asynchronous I/O operations. Although the issue does not appear to be exploited in the wild yet, it poses a risk of denial-of-service (DoS) through kernel crashes if malicious or malformed requests are submitted to vulnerable kernels. The vulnerability is technical and requires crafted input to trigger, but it can be exploited locally or remotely if an attacker can submit io_uring requests with invalid file descriptors.

For European organizations, the primary impact of CVE-2024-39371 is the potential for denial-of-service attacks against Linux-based systems that utilize the io_uring interface for asynchronous I/O. This includes servers, cloud infrastructure, and embedded devices running vulnerable kernel versions. A successful exploitation leads to kernel crashes, causing service interruptions and potential downtime. This can affect critical infrastructure, web servers, database servers, and any application relying on Linux kernel stability. While the vulnerability does not directly lead to privilege escalation or data leakage, the resulting system instability can disrupt business operations and availability. Organizations in sectors such as finance, healthcare, telecommunications, and government, which heavily depend on Linux servers, may face operational risks. Additionally, the vulnerability could be leveraged as part of a multi-stage attack to degrade system reliability or as a distraction while other attacks are conducted. Given the widespread use of Linux in European data centers and cloud environments, the impact is significant if unpatched systems remain exposed. However, exploitation requires the ability to submit crafted io_uring requests, which may limit remote exploitation vectors unless exposed services allow such interactions.

European organizations should implement the following specific mitigation steps: 1) Identify and inventory all Linux systems using kernel versions prior to the patch that include the vulnerable io_uring implementation. 2) Apply the official Linux kernel patches or upgrade to a kernel version that includes the fix for CVE-2024-39371 as soon as possible to prevent exploitation. 3) Restrict access to systems and services that allow submission of io_uring requests, especially from untrusted or external networks, to reduce the attack surface. 4) Monitor system logs and kernel oops reports for signs of NULL pointer dereferences or unexpected crashes related to io_uring operations, which may indicate attempted exploitation. 5) Employ kernel hardening techniques such as kernel lockdown and seccomp filters to limit the ability of unprivileged users or processes to invoke io_uring syscalls. 6) For cloud and container environments, ensure that container runtimes and orchestration platforms are configured to prevent untrusted containers from accessing io_uring interfaces or submitting malformed requests. 7) Conduct regular vulnerability scanning and penetration testing focused on asynchronous I/O interfaces to detect potential exploitation attempts. These steps go beyond generic advice by focusing on access control to io_uring interfaces, proactive monitoring for kernel faults, and environment-specific hardening.