CVE-2025-21694 is a vulnerability identified in the Linux kernel, specifically within the fs/proc subsystem's __read_vmcore function. This function is involved in reading the vmcore, which is a memory dump generated during kernel crash dumps (kdump). The vulnerability relates to a softlockup condition occurring during the execution of __read_vmcore. A softlockup is a situation where a CPU is stuck in a loop without yielding control, causing the system to become unresponsive or severely degraded. Although a previous patch (commit 5cbcb62dddf5) reduced the frequency of these softlockups, they still occasionally occur, particularly in memory-constrained environments such as when processing kdump images. The issue arises because the second loop in __read_vmcore, despite having natural sleep points, does not always yield CPU time effectively, leading to potential interference with critical kernel operations like Read-Copy-Update (RCU) memory freeing. This interference can cause the crashdump process to hang, preventing successful memory dump collection and complicating post-crash analysis. The fix involves adding a cond_resched() call in the second loop to explicitly yield the CPU, thereby preventing softlockups and ensuring smoother kdump operation. This vulnerability affects multiple Linux kernel versions identified by specific commit hashes, indicating it is present in several recent kernel builds prior to the fix. No known exploits are currently reported in the wild, and no CVSS score has been assigned yet.

For European organizations relying on Linux-based systems, especially those using kdump for crash diagnostics and forensic analysis, this vulnerability could impair their ability to capture reliable crash dumps during system failures. This can hinder incident response and root cause analysis, potentially delaying recovery from critical outages. Systems operating in memory-constrained environments, such as embedded devices, virtual machines with limited resources, or containerized workloads, are particularly susceptible. While the vulnerability does not directly enable remote code execution or privilege escalation, the denial of service manifested as system hangs or unresponsive states during crash dump collection can disrupt business continuity. Organizations in sectors with high availability requirements—such as finance, healthcare, telecommunications, and critical infrastructure—may face operational risks if crash diagnostics are compromised. Additionally, the inability to obtain crash dumps may reduce forensic evidence availability during security incident investigations, impacting compliance with regulatory frameworks prevalent in Europe (e.g., GDPR, NIS Directive).

European organizations should prioritize updating their Linux kernels to versions that include the patch addressing CVE-2025-21694. Given the vulnerability affects the __read_vmcore function used during kdump, organizations should verify that their crash dump mechanisms are functioning correctly post-update by performing controlled crash dump tests in memory-constrained environments. For systems where immediate kernel upgrades are not feasible, consider increasing available memory for kdump operations or adjusting kernel parameters to reduce memory pressure during crash dumps. Monitoring system logs for softlockup warnings related to __read_vmcore can help detect attempts to exploit or encounter this issue. Additionally, organizations should implement robust backup and recovery procedures to mitigate the impact of potential system hangs during crash events. For embedded or specialized Linux deployments, coordinate with vendors to obtain patched kernel versions or backported fixes. Finally, integrate this vulnerability into vulnerability management and patching workflows to ensure timely remediation.