CVE-2024-26603 is a vulnerability identified in the Linux kernel's x86 floating-point unit (FPU) handling code, specifically related to the XSAVE/XRSTOR instructions used for saving and restoring extended processor state. The issue arises because the kernel previously relied on user-space provided information (fx_sw->xstate_size) to determine the size of the XSAVE buffer to fault in during context restoration. Since this size can be manipulated by user-space, an attacker could craft a malicious sigreturn frame where the reported buffer size is smaller than the actual size required by the valid feature bits (fx_sw->xfeatures). Additionally, user-space could unmap parts of the signal frame's FPU buffer, causing the kernel to attempt to restore state from an unmapped memory region. This leads to a fault during the xrstor operation. The kernel's fault_in_readable function incorrectly succeeds because it only checks up to the manipulated smaller size, causing the kernel to retry the xrstor operation repeatedly, resulting in an infinite loop (spinlock). This effectively causes a denial of service (DoS) by hanging the affected process or potentially the entire system. The patch fixes this by making the kernel fault in the maximum size required by XRSTOR (fpstate->user_size) rather than trusting user-space input, preventing the infinite loop and ensuring proper memory access validation during state restoration. No known exploits are reported in the wild as of the publication date, and the vulnerability affects Linux kernel versions identified by the commit hashes listed. This vulnerability is a logic flaw in kernel memory validation and handling of user-supplied data during context switching and signal frame restoration on x86 architectures.

For European organizations, this vulnerability primarily poses a risk of denial of service attacks against Linux systems running vulnerable kernel versions. Since Linux is widely used in servers, cloud infrastructure, and embedded devices across Europe, exploitation could disrupt critical services by causing processes or entire systems to hang indefinitely. This could impact availability of web services, internal applications, and infrastructure components, leading to operational downtime and potential financial losses. While the vulnerability does not appear to allow privilege escalation or code execution, the DoS effect could be leveraged in targeted attacks against high-value infrastructure, especially in sectors relying heavily on Linux-based systems such as finance, telecommunications, government, and critical infrastructure. The lack of known exploits reduces immediate risk, but the ease of triggering the infinite loop by crafting specific signal frames means attackers with local access or the ability to run code on affected systems could exploit it. European organizations with multi-tenant environments or shared hosting could also face risks if attackers cause denial of service conditions affecting other tenants. Overall, the impact is focused on availability disruption rather than confidentiality or integrity compromise.

To mitigate this vulnerability, European organizations should prioritize updating their Linux kernels to versions that include the patch for CVE-2024-26603 as soon as vendor updates are available. Kernel updates should be tested and deployed promptly in production environments. For environments where immediate patching is not feasible, organizations should restrict untrusted users from executing code or sending crafted signals that could trigger the vulnerability. Implementing strict access controls and containerization can limit the ability of attackers to exploit this flaw. Monitoring system logs for unusual kernel faults or process hangs related to FPU state restoration may help detect attempted exploitation. Additionally, organizations should review and harden signal handling and process privilege boundaries to reduce the attack surface. Security teams should also ensure that incident response plans include procedures for addressing denial of service conditions caused by kernel-level faults. Finally, maintaining up-to-date intrusion detection and prevention systems that can identify anomalous behavior related to kernel faults can provide early warning of exploitation attempts.