CVE-2024-35815 is a vulnerability identified in the Linux kernel, specifically within the asynchronous I/O (AIO) subsystem. The issue arises in the fs/aio code path where the function kiocb_set_cancel_fn() is called with a pointer that may reference a struct kiocb not embedded inside the expected struct aio_kiocb. The vulnerability stems from the order of operations in the code: depending on the compiler behavior, a read of req->ki_ctx can occur either before or after a critical IOCB_AIO_RW flag check. This flag check is intended to verify that the request is a read or write AIO operation. If the read of req->ki_ctx happens before the IOCB_AIO_RW test, it can lead to the use of an invalid or improperly cast pointer. This can cause undefined behavior, including potential memory corruption or information disclosure. The fix involves reordering the code to ensure the IOCB_AIO_RW test is always performed before accessing req->ki_ctx, thereby preventing unsafe pointer dereferencing. The affected versions correspond to various Linux kernel commits prior to the patch. No known exploits are reported in the wild as of the publication date (May 17, 2024). However, given the kernel-level nature of the flaw and its involvement with asynchronous I/O operations, exploitation could allow local attackers to cause denial of service or potentially escalate privileges by corrupting kernel memory or bypassing kernel-level protections. This vulnerability requires local access and likely some level of user interaction to trigger the vulnerable code path, but it does not require authentication beyond local user privileges. The absence of a CVSS score necessitates a severity assessment based on the technical details and potential impact.

For European organizations, this vulnerability poses a risk primarily to systems running vulnerable Linux kernel versions, which are widespread across servers, cloud infrastructure, and embedded devices. Exploitation could lead to denial of service conditions, impacting availability of critical services, or privilege escalation, compromising system integrity and confidentiality. Organizations relying on Linux for critical infrastructure, including financial institutions, telecommunications, government agencies, and cloud service providers, could face operational disruptions or data breaches if attackers leverage this flaw. The vulnerability's exploitation complexity is moderate, requiring local access and triggering specific asynchronous I/O operations, which may limit remote exploitation but does not eliminate risk from insider threats or compromised accounts. Given the prevalence of Linux in European data centers and enterprise environments, unpatched systems could be targeted for lateral movement or privilege escalation within networks. Additionally, the vulnerability could affect embedded Linux devices used in industrial control systems or IoT deployments, potentially impacting sectors like manufacturing or energy. The lack of known exploits reduces immediate threat but does not preclude future weaponization, making timely patching critical to maintaining security posture.

European organizations should prioritize the following mitigation steps: 1) Identify and inventory all Linux systems running affected kernel versions, including servers, virtual machines, containers, and embedded devices. 2) Apply the official Linux kernel patches that reorder the IOCB_AIO_RW check before accessing req->ki_ctx as soon as they become available from trusted sources or distribution vendors. 3) For systems where immediate patching is not feasible, implement compensating controls such as restricting local user access, enforcing strict privilege separation, and monitoring for anomalous asynchronous I/O activity that could indicate exploitation attempts. 4) Employ kernel integrity monitoring and runtime security tools capable of detecting abnormal kernel memory access or crashes related to AIO operations. 5) Maintain up-to-date backups and incident response plans to quickly recover from potential denial of service or compromise scenarios. 6) Engage with Linux distribution vendors and security advisories to track patch releases and vulnerability disclosures. 7) Educate system administrators and security teams about the vulnerability specifics to enhance detection and response capabilities. These targeted actions go beyond generic advice by focusing on asynchronous I/O subsystem awareness, local access controls, and kernel-level monitoring tailored to this vulnerability.