CVE-2021-47464 is a high-severity vulnerability identified in the Linux kernel's audit subsystem, specifically within the audit_filter_rules function. The flaw is a possible null-pointer dereference caused by an incorrect assumption that the 'ctx' (context) pointer could never be null. This vulnerability falls under CWE-476 (NULL Pointer Dereference), which can lead to system crashes or denial of service (DoS) conditions when exploited. The audit subsystem is responsible for monitoring and logging security-relevant events on Linux systems, and a flaw here can impact system stability and security monitoring capabilities. The CVSS v3.1 score is 7.4, indicating a high severity level, with the vector AV:L/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H. This means the attack vector requires local access (AV:L), high attack complexity (AC:H), no privileges required (PR:N), no user interaction (UI:N), unchanged scope (S:U), and impacts confidentiality, integrity, and availability at a high level (C:H/I:H/A:H). Although no known exploits are currently reported in the wild, the vulnerability could be leveraged by a local attacker to cause system crashes or potentially escalate privileges by disrupting audit functionality. The affected versions are identified by specific kernel commit hashes, indicating the flaw is present in certain Linux kernel builds prior to the patch. The vulnerability was published on May 22, 2024, and has been acknowledged by the Linux project with a fix applied to prevent the null-pointer dereference by properly handling the 'ctx' pointer in audit_filter_rules.

For European organizations, this vulnerability poses a significant risk, especially for those relying heavily on Linux-based infrastructure for critical services, including servers, cloud environments, and embedded systems. The audit subsystem is crucial for compliance with regulations such as GDPR, NIS Directive, and other cybersecurity frameworks that mandate robust logging and monitoring. Exploitation could lead to denial of service, disrupting business operations and potentially causing loss of audit data integrity, which could hinder forensic investigations and compliance reporting. Given the high impact on confidentiality, integrity, and availability, attackers could leverage this flaw to disrupt security monitoring or cause system instability, affecting sectors like finance, healthcare, government, and critical infrastructure. The requirement for local access and high attack complexity somewhat limits remote exploitation but does not eliminate risk from insider threats or attackers who have gained initial footholds. The absence of known exploits in the wild reduces immediate urgency but does not preclude future exploitation attempts.

European organizations should prioritize updating their Linux kernel versions to the fixed releases that address CVE-2021-47464. Since the vulnerability requires local access and high attack complexity, organizations should also strengthen internal access controls and monitoring to detect and prevent unauthorized local access. Implement strict user privilege management and employ kernel integrity monitoring tools to detect anomalous behavior related to the audit subsystem. Regularly audit and verify the integrity of audit logs to ensure they have not been tampered with. For environments where immediate patching is challenging, consider disabling or restricting audit subsystem features temporarily, if feasible, to reduce exposure. Additionally, organizations should enhance endpoint detection and response (EDR) capabilities to identify potential exploitation attempts and maintain robust incident response plans tailored to kernel-level vulnerabilities. Coordination with Linux distribution vendors for timely patch deployment and monitoring security advisories is essential.