CVE-2024-38618 is a medium-severity vulnerability identified in the Linux kernel's ALSA (Advanced Linux Sound Architecture) timer subsystem. The issue arises because the ALSA timer did not enforce a lower bound on the start tick time for high-resolution timers (hrtimers). Specifically, it allowed extremely small start tick durations, such as 1 tick with a 1 nanosecond resolution. This improper configuration can lead to an unexpected Read-Copy-Update (RCU) stall, a kernel synchronization mechanism. The stall occurs because the timer callback repeatedly queues expiration updates without proper delay, causing the kernel's RCU subsystem to stall. This behavior was discovered through fuzz testing. The vulnerability does not directly impact confidentiality or integrity but affects system availability by potentially causing kernel stalls or hangs. The patch introduced enforces a sanity check that rejects timer start tick times below 100 microseconds, which is a practical lower limit that prevents the stall while maintaining timer functionality. The vulnerability affects Linux kernel versions prior to the patch commit identified by the hash 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2. The CVSS v3.1 base score is 5.3 (medium), reflecting a network attack vector with low attack complexity, no privileges required, no user interaction, and impact limited to availability. No known exploits are currently reported in the wild.

For European organizations, this vulnerability primarily threatens system availability on Linux-based infrastructure, including servers, embedded devices, and workstations using ALSA for sound management. While the impact is limited to availability and does not compromise data confidentiality or integrity, an RCU stall can cause kernel hangs or system freezes, leading to downtime. This can disrupt critical services, especially in environments relying on real-time audio processing, multimedia applications, or embedded Linux systems in industrial control, telecommunications, or IoT devices. Organizations with large Linux deployments, such as cloud service providers, telecom operators, and enterprises using Linux servers, may experience service interruptions if vulnerable kernels are exploited or triggered inadvertently. However, exploitation does not require authentication or user interaction, increasing the risk of remote triggering if the timer interface is exposed. The absence of known exploits reduces immediate risk but does not eliminate the potential for future attacks or accidental system instability.

European organizations should promptly apply the official Linux kernel patch that enforces the 100 microsecond lower bound on ALSA timer start tick times. Kernel updates should be prioritized in maintenance cycles, especially for systems handling audio or real-time processing. System administrators should audit their Linux kernel versions and update to the patched release or later. For embedded or specialized devices where kernel updates are challenging, consider disabling or restricting ALSA timer usage or implementing kernel-level monitoring to detect abnormal timer configurations or RCU stalls. Additionally, organizations should implement robust system monitoring and alerting to detect kernel stalls or hangs early, enabling rapid remediation. Network exposure of ALSA timer interfaces should be minimized or protected via firewall rules and access controls to reduce remote exploitation risk. Finally, maintain regular backups and incident response plans to mitigate potential downtime consequences.