CVE-2023-52854 is a use-after-free (UAF) vulnerability identified in the Linux kernel's padata subsystem, specifically affecting the padata_free_shell() function's reference count handling. The padata subsystem is responsible for parallelizing cryptographic and other asynchronous operations to improve performance. The vulnerability arises under high-load conditions on arm64 architectures during execution of the pcrypt_aead01 test in the Linux Test Project (LTP). The issue is caused by improper synchronization and reference counting when freeing padata data structures. In the vulnerable scenario, after invoking padata_free_shell(), the reference count on the padata data structure (pd->refcnt) may be decremented incorrectly due to delayed execution of softirqs (software interrupts) caused by system load. This leads to the pd structure being freed prematurely while still being accessed by the padata_serial_worker function, resulting in a use-after-free condition. The root cause is that local_bh_enable(), which re-enables bottom halves (softirqs), takes longer than expected under high load, allowing padata_free_shell() to free the pd structure before padata_serial_worker finishes accessing it. The fix involves adding a refcount_dec_and_test call before freeing the padata data structure in padata_free_shell(), ensuring proper reference count decrement and preventing premature freeing. This vulnerability is specific to certain Linux kernel versions as identified by commit hashes and affects arm64 environments under high load. No known exploits are currently reported in the wild. The vulnerability does not have an assigned CVSS score yet but is recognized and published by the Linux project and CISA. Exploitation requires triggering specific kernel code paths under high load, which may limit ease of exploitation but still poses a risk to systems running vulnerable kernel versions, especially those using the padata subsystem for cryptographic operations.

For European organizations, the impact of CVE-2023-52854 can be significant in environments relying on affected Linux kernel versions, particularly on arm64 hardware platforms such as servers, cloud infrastructure, and embedded systems. The use-after-free vulnerability can lead to kernel crashes (denial of service), system instability, or potentially privilege escalation if exploited by a local attacker with the ability to trigger the vulnerable code paths. This could disrupt critical services, especially in sectors like finance, telecommunications, healthcare, and government where Linux-based systems are prevalent. Additionally, organizations running high-load workloads or cryptographic operations on arm64 Linux servers may be more susceptible. Although no public exploits are known, the vulnerability's presence in the kernel means attackers with local access could leverage it to compromise system integrity or availability. This risk is heightened in multi-tenant cloud environments or shared infrastructure common in European data centers. The vulnerability also poses a risk to embedded Linux devices used in industrial control systems or IoT deployments within Europe, potentially affecting operational technology environments.

European organizations should prioritize updating their Linux kernel to versions where this vulnerability is patched, applying vendor-provided security updates or mainline kernel patches that include the refcount handling fix in padata_free_shell(). For environments where immediate patching is not feasible, mitigating risk includes limiting untrusted local user access to affected systems, restricting high-load cryptographic workloads that trigger the vulnerable code path, and monitoring system logs for kernel errors or crashes indicative of exploitation attempts. Organizations should also audit their use of arm64 Linux systems and assess exposure based on workload profiles. Employing kernel hardening features such as Kernel Address Space Layout Randomization (KASLR), Kernel Page Table Isolation (KPTI), and enabling kernel lockdown modes can reduce exploitation likelihood. Additionally, implementing strict access controls, using containerization or virtualization to isolate workloads, and continuous monitoring for anomalous kernel behavior will help detect and prevent exploitation. Collaboration with Linux distribution vendors to receive timely patches and guidance is critical. Finally, testing patches in staging environments before deployment ensures stability and compatibility.