CVE-2025-21739 is a high-severity use-after-free vulnerability in the Linux kernel's UFS (Universal Flash Storage) SCSI driver subsystem. The flaw arises during the initialization and cleanup phases of the UFS host bus adapter (ufs_hba) driver. Specifically, the vulnerability occurs because the crypto profile data structure (struct ufs_hba::crypto_profile), which is allocated as part of the ufs_hba and underlying ufshcd structures, is freed prematurely during error handling or driver removal. The cleanup handler for the crypto profile is registered with the platform device and is invoked after the crypto profile memory has already been released, leading to a use-after-free condition. This can cause kernel memory corruption, potentially allowing an attacker with limited privileges (local access with low privileges) to escalate privileges, cause denial of service through kernel crashes, or execute arbitrary code in kernel context. The root cause is the improper ordering of resource deallocation: the crypto profile is destroyed after the underlying SCSI device memory has been freed. The fix involves changing the ufshcd_alloc_host() function to register a devres action that ensures the crypto profile and other ufs_hba-owned resources are cleaned up before the SCSI device is destroyed, preventing the use-after-free. This fix also removes the need for explicit calls to ufshcd_dealloc_host() and prevents potential memory leaks in related drivers. The vulnerability is tracked under CWE-416 (Use After Free) and has a CVSS 3.1 base score of 7.8, reflecting high impact on confidentiality, integrity, and availability with low attack complexity but requiring local privileges and no user interaction.

For European organizations, this vulnerability poses a significant risk especially for those relying on Linux-based systems with UFS storage devices, commonly found in embedded systems, mobile devices, and some server environments. Exploitation could allow local attackers to escalate privileges to root, leading to full system compromise. This could result in unauthorized access to sensitive data, disruption of critical services, and potential lateral movement within networks. Given the kernel-level nature of the flaw, successful exploitation could undermine the integrity and availability of affected systems, impacting sectors such as telecommunications, manufacturing, and critical infrastructure that utilize Linux-based embedded devices. The vulnerability's requirement for local access limits remote exploitation but insider threats or compromised user accounts could leverage this flaw. Additionally, the flaw could be exploited to create persistent backdoors or disrupt system operations, affecting compliance with European data protection regulations and operational resilience requirements.

European organizations should prioritize patching affected Linux kernel versions as soon as updates become available from trusted distributors. Since the vulnerability involves kernel driver internals, applying vendor-supplied kernel patches or upgrading to fixed kernel versions is the most effective mitigation. Organizations should audit their environments to identify systems using UFS storage and the affected kernel versions. For embedded devices or systems where immediate patching is not feasible, consider restricting local access to trusted users only and employing kernel-level security modules (e.g., SELinux, AppArmor) to limit the impact of potential exploits. Additionally, implement strict access controls and monitoring to detect unusual local activity that could indicate exploitation attempts. Regularly review and update device firmware and drivers to ensure they incorporate the latest security fixes. Finally, coordinate with hardware and OS vendors to confirm that all components in the supply chain are updated to mitigate this vulnerability.