CVE-2023-52983 is a high-severity use-after-free (UAF) vulnerability in the Linux kernel's block layer, specifically affecting the Budget Fair Queueing (BFQ) I/O scheduler implementation. The vulnerability arises in the function bic_set_bfqq(), which manages the association between a bfq_io_cq (bic) structure and its bfq_queue (bfqq). After a prior fix (commit 64dc8c732f5c), bic->bfqq is accessed in bic_set_bfqq(), but under certain conditions, bic->bfqq may have already been freed before this function is called, leading to a use-after-free scenario. This can cause the kernel to access freed memory, potentially resulting in memory corruption, system crashes, or arbitrary code execution within kernel context. The root cause is that the bfqq object is freed after bic_set_bfqq() is called, but the function still accesses the freed bfqq pointer. The fix involves ensuring that bfqq is always freed after bic_set_bfqq(), preventing access to freed memory. The vulnerability is tracked under CWE-416 (Use After Free) and has a CVSS v3.1 score of 7.8, indicating high severity. Exploitation requires local privileges (AV:L), low attack complexity (AC:L), and privileges (PR:L), but no user interaction (UI:N). The impact on confidentiality, integrity, and availability is high (C:H/I:H/A:H), meaning a successful exploit could lead to full system compromise, including privilege escalation and denial of service. No known exploits are reported in the wild as of the publication date. The affected versions correspond to specific Linux kernel commits prior to the fix. This vulnerability is critical for systems relying on the BFQ I/O scheduler, commonly used in desktop and server Linux distributions for fair disk I/O scheduling.

For European organizations, this vulnerability poses a significant risk, especially for those running Linux-based servers, desktops, or embedded systems using the BFQ I/O scheduler. Successful exploitation could allow a local attacker to escalate privileges to kernel level, leading to full system compromise, data breaches, or disruption of critical services. This is particularly concerning for sectors such as finance, healthcare, government, and critical infrastructure, where Linux servers are prevalent. The high impact on confidentiality, integrity, and availability means sensitive data could be exposed or altered, and systems could be rendered unavailable. Additionally, the vulnerability could be leveraged as a foothold for lateral movement within networks. Although exploitation requires local access and some privileges, insider threats or attackers who gain initial access through other means could exploit this flaw to escalate privileges. The lack of known exploits in the wild currently reduces immediate risk but does not eliminate the threat, as proof-of-concept or weaponized exploits could emerge. European organizations should prioritize patching to mitigate potential attacks and maintain system integrity.

1. Apply the official Linux kernel patches that fix CVE-2023-52983 as soon as they are available from trusted sources or distribution vendors. 2. Identify and inventory systems using the BFQ I/O scheduler by checking kernel configuration and runtime settings (e.g., via /sys/block/<device>/queue/scheduler). 3. Temporarily switch to an alternative I/O scheduler (such as CFQ or noop) on critical systems where patching is delayed, to reduce exposure. 4. Restrict local user privileges and enforce strict access controls to minimize the risk of local exploitation. 5. Monitor system logs and kernel messages for unusual behavior or crashes that could indicate exploitation attempts. 6. Employ kernel hardening techniques such as Kernel Address Space Layout Randomization (KASLR) and Control Flow Integrity (CFI) where supported to increase exploitation difficulty. 7. Maintain up-to-date intrusion detection and endpoint protection solutions capable of detecting anomalous kernel-level activity. 8. Conduct regular security audits and vulnerability assessments focusing on kernel vulnerabilities and privilege escalation paths. 9. Educate system administrators and security teams about this vulnerability and the importance of timely patching and mitigation.