CVE-2024-56681 is a vulnerability identified in the Linux kernel's cryptographic subsystem, specifically within the bcm (Broadcom) crypto module. The issue lies in the ahash_hmac_init function, which is responsible for initializing HMAC (Hash-based Message Authentication Code) operations. The vulnerability arises because ahash_hmac_init does not properly handle error returns from the underlying ahash_init function. In particular, if ahash_init fails—such as returning -ENOMEM due to memory allocation failure—ahash_hmac_init incorrectly returns success (OK) instead of propagating the error. This improper error handling can lead to cryptographic operations proceeding under faulty assumptions, potentially resulting in incorrect cryptographic computations or failures that are not properly reported to the calling processes. Although the vulnerability does not directly expose a memory corruption or code execution flaw, it undermines the reliability and correctness of cryptographic operations within the kernel. This could have downstream effects on any kernel or user-space components relying on the bcm crypto module for HMAC computations, including authentication, integrity verification, and secure communications. The vulnerability affects specific Linux kernel versions identified by the commit hash 9d12ba86f818aa9cfe9f01b750336aa441f2ffa2, and was published on December 28, 2024. No known exploits are currently reported in the wild, and no CVSS score has been assigned yet. The fix involves adding proper error checking in ahash_hmac_init to ensure that failures in ahash_init are correctly propagated and handled.

For European organizations, the impact of CVE-2024-56681 depends largely on their reliance on the affected Linux kernel versions and the bcm crypto module for critical cryptographic operations. Since the vulnerability affects the integrity of HMAC initialization, it could lead to subtle cryptographic failures that may compromise the integrity verification of data or authentication mechanisms relying on HMAC. This could affect secure communications, VPNs, or any system components that use the bcm crypto module for cryptographic assurances. While it does not appear to allow direct privilege escalation or remote code execution, the risk lies in degraded cryptographic guarantees, which could be exploited in multi-stage attacks or lead to denial of service if cryptographic operations fail silently. European organizations with infrastructure running affected Linux kernels—especially those in telecommunications, cloud services, and critical infrastructure sectors—may face operational risks or compliance issues if cryptographic integrity is compromised. Given the widespread use of Linux in servers and embedded devices, the scope is broad, but the actual impact depends on the deployment of the bcm crypto module and kernel versions in use.

Organizations should promptly identify and inventory systems running the affected Linux kernel versions, particularly those utilizing the bcm crypto module for cryptographic operations. Applying the official Linux kernel patches that correct the error handling in ahash_hmac_init is essential. Since no patch links are provided, organizations should monitor the official Linux kernel repositories and security advisories for the relevant patch commits. Additionally, system administrators should audit cryptographic logs and monitor for unusual authentication or integrity verification failures that could indicate exploitation attempts or operational issues. For critical systems, consider implementing layered cryptographic validation or fallback mechanisms to detect and handle cryptographic initialization failures gracefully. Testing updates in staging environments before deployment can help ensure stability. Finally, maintain up-to-date backups and incident response plans to address any potential cryptographic failures impacting system availability or data integrity.