CVE-2025-37880 is a vulnerability identified in the Linux kernel related to the behavior of the sched_yield system call when operating in time-travel mode. Time-travel mode is a specialized kernel feature used primarily in User-Mode Linux (UML) or similar environments that allow deterministic replay or simulation of process execution by controlling the passage of time within the kernel. The vulnerability arises because sched_yield, which is intended to voluntarily relinquish the CPU to allow other processes to run, does not function correctly in time-travel mode. Specifically, since no real time passes in this mode, sched_yield calls by userspace applications may not cause actual scheduling changes. This issue was observed in a scenario involving a poorly implemented userspace spinlock under AddressSanitizer (ASAN), which relies on sched_yield to avoid busy waiting. Due to the lack of effective yielding, processes can experience extreme slowdowns or even deadlocks depending on kernel configuration parameters such as CONFIG_UML_MAX_USERSPACE_ITERATIONS. The underlying problem is that sched_yield does not account for time progression in time-travel mode, leading to starvation or deadlock conditions. The fix implemented involves modifying the kernel to account for process execution time whenever sched_yield is invoked, ensuring that the scheduler behaves as expected even in time-travel mode. This vulnerability is specific to specialized kernel configurations and use cases involving time-travel mode, which is not common in standard Linux deployments but may be used in advanced debugging, testing, or virtualization scenarios.

For European organizations, the impact of CVE-2025-37880 is likely limited to environments that utilize User-Mode Linux or similar time-travel kernel modes, often in development, testing, or research contexts. Organizations relying on these specialized kernel features for debugging, security testing, or virtualization may experience severe performance degradation or deadlocks, potentially halting critical testing or simulation workflows. This could delay development cycles or compromise the reliability of security analyses that depend on deterministic replay. However, standard Linux server and desktop deployments are unlikely to be affected, as time-travel mode is not enabled by default and is not commonly used in production environments. The absence of known exploits in the wild further reduces immediate risk. Nonetheless, organizations involved in kernel development, security research, or advanced virtualization within Europe should be aware of this vulnerability to avoid disruptions. If unmitigated, the vulnerability could lead to denial of service conditions in affected environments, impacting availability and operational continuity.

To mitigate CVE-2025-37880, European organizations should: 1) Identify and inventory systems running Linux kernels with time-travel mode enabled, particularly those using User-Mode Linux or similar environments. 2) Apply the official kernel patch or update to the latest Linux kernel version that includes the fix accounting for process execution time during sched_yield calls. 3) Review and test userspace applications, especially those using spinlocks or synchronization primitives relying on sched_yield, to ensure compatibility with the patched kernel behavior. 4) For environments where patching is not immediately feasible, consider disabling time-travel mode or limiting the use of sched_yield in userspace to prevent deadlocks. 5) Implement monitoring to detect unusual process scheduling behavior or performance degradation indicative of this issue. 6) Engage with Linux kernel maintainers or vendors for backported fixes if using long-term support kernels. These steps go beyond generic advice by focusing on the specialized nature of the vulnerability and the environments where it manifests.