CVE-2025-37808 is a vulnerability identified in the Linux kernel's cryptographic subsystem, specifically related to the null algorithm implementation within the kernel's crypto API. The issue arises from the use of mutex locks to protect the default null algorithm, which may be freed in a softirq (software interrupt) context via the asynchronous crypto framework (af_alg). Mutexes are not safe to use in softirq contexts because they can sleep, which is disallowed in interrupt context and can lead to deadlocks or race conditions. The vulnerability is mitigated by replacing mutex locks with spin locks, which are suitable for use in interrupt contexts because they do not sleep and instead spin while waiting for the lock to become available. This change prevents potential race conditions or use-after-free scenarios that could arise if the null algorithm is freed concurrently during cryptographic operations in softirq context. Although the null algorithm itself performs no encryption or decryption (it effectively passes data through unchanged), the vulnerability lies in the kernel synchronization mechanism, which could lead to kernel instability, crashes, or potentially exploitable conditions such as privilege escalation or denial of service if an attacker can trigger the race condition. The affected versions are identified by a specific commit hash, indicating that this vulnerability is present in certain recent Linux kernel builds prior to the patch. No known exploits are reported in the wild as of the publication date (May 8, 2025), and no CVSS score has been assigned yet. The vulnerability is technical and low-level, requiring knowledge of kernel internals and the crypto API to exploit.

For European organizations, the impact of CVE-2025-37808 depends largely on their use of Linux-based systems, especially those employing cryptographic operations within kernel space. Many enterprises, cloud providers, and critical infrastructure operators in Europe rely heavily on Linux servers and embedded systems. If exploited, this vulnerability could lead to kernel crashes or denial of service, disrupting services and potentially causing data loss or downtime. In worst-case scenarios, if an attacker can leverage the race condition to escalate privileges, it could compromise the confidentiality and integrity of sensitive data. This is particularly concerning for sectors such as finance, healthcare, telecommunications, and government agencies, which handle sensitive personal and operational data. However, since the null algorithm is a no-op cryptographic algorithm, the direct cryptographic impact is minimal, but the kernel-level synchronization flaw could be leveraged in complex attack chains. The absence of known exploits suggests that the threat is currently theoretical but should be addressed promptly to prevent future exploitation. Organizations running custom or older Linux kernels are at higher risk if they have not applied the patch.

European organizations should immediately verify their Linux kernel versions and identify if they are running affected builds corresponding to the specified commit hash. Applying the official Linux kernel patch that replaces mutexes with spin locks in the null algorithm implementation is the primary mitigation step. For organizations using vendor-specific Linux distributions, they should monitor vendor advisories for backported patches and apply them promptly. Additionally, organizations should audit their cryptographic usage in kernel space to assess exposure and consider disabling or restricting the use of the null algorithm if not required. Implementing kernel hardening measures such as Kernel Address Space Layout Randomization (KASLR), Control Flow Integrity (CFI), and enabling kernel lockdown modes can reduce exploitation risk. Monitoring system logs for kernel warnings or crashes related to crypto operations can help detect attempts to trigger the vulnerability. Finally, maintaining a robust patch management process and testing kernel updates in staging environments before production deployment will ensure timely and safe remediation.