CVE-2025-21749 is a vulnerability identified in the Linux kernel's implementation of the ROSE (Radio Amateur Satellite Corporation) protocol stack, specifically within the rose_bind() function. The issue arises due to the lack of proper locking mechanisms on the socket during the bind operation. This flaw was discovered after syzbot, an automated kernel fuzzer, reported a soft lockup occurring in the rose_loopback_timer() function when bind() was called concurrently from multiple threads. The root cause is a race condition where multiple threads attempt to bind the same socket simultaneously without synchronization, leading to a deadlock or soft lockup state. The fix involves introducing a lock on the socket within rose_bind() to prevent concurrent access and ensure thread safety. This vulnerability affects certain Linux kernel versions identified by specific commit hashes, indicating it is present in recent kernel development branches prior to the patch. Although the ROSE protocol is niche and primarily used in amateur radio and satellite communications, the vulnerability exposes a concurrency flaw in the kernel's network stack that could be triggered by local processes. There are no known exploits in the wild at this time, and the vulnerability requires local code execution to trigger the bind() calls concurrently. The absence of a CVSS score suggests it is a newly disclosed issue with limited impact surface, but the underlying concurrency problem could potentially be leveraged for denial of service or system instability under specific conditions.

For European organizations, the impact of CVE-2025-21749 is generally limited due to the specialized nature of the ROSE protocol, which is not commonly used in mainstream enterprise environments. However, organizations involved in amateur radio, satellite communications, or research institutions using Linux systems with ROSE protocol support could experience system instability or denial of service if this vulnerability is exploited. The soft lockup could lead to kernel hangs or degraded system performance, affecting availability of critical services running on affected Linux hosts. Since the vulnerability requires local access and concurrent bind() calls, the risk is higher in multi-user or multi-threaded environments where untrusted users or processes could attempt to trigger the flaw. European entities with Linux-based infrastructure in telecommunications, research, or specialized networking may need to assess exposure. The vulnerability does not appear to compromise confidentiality or integrity directly but could be used as a vector to disrupt operations or escalate issues in complex environments.

To mitigate CVE-2025-21749, European organizations should: 1) Apply the official Linux kernel patches that introduce socket locking in rose_bind() as soon as they become available in stable kernel releases. 2) Audit systems for use of the ROSE protocol and disable or remove support if not required, reducing the attack surface. 3) Restrict local user permissions to prevent untrusted users from executing concurrent bind() calls on sockets, particularly in multi-user systems. 4) Monitor kernel logs and system behavior for signs of soft lockups or unusual socket activity related to ROSE. 5) In environments where ROSE is essential, implement additional concurrency controls at the application level to avoid triggering the race condition. 6) Maintain up-to-date kernel versions and subscribe to Linux kernel security advisories to promptly respond to any emerging exploit reports.