CVE-2024-21594 is a heap-based buffer overflow vulnerability identified in the Network Services Daemon (NSD) component of Juniper Networks Junos OS, specifically affecting SRX 5000 Series devices. This vulnerability allows an authenticated, low-privileged local attacker to repeatedly execute a specific command that corrupts memory, ultimately causing the Flow Processing Daemon (flowd) to crash. The crash results in a Denial of Service (DoS) condition, requiring a restart of the NSD process to restore normal operation. The vulnerability affects multiple versions of Junos OS, including all versions earlier than 20.4R3-S6, 21.1 versions earlier than 21.1R3-S5, 21.2 versions earlier than 21.2R3-S4, 21.3 versions earlier than 21.3R3-S3, 21.4 versions earlier than 21.4R3-S3, 22.1 versions earlier than 22.1R3-S1, 22.2 versions earlier than 22.2R3, and 22.3 versions earlier than 22.3R2. The vulnerability is classified under CWE-122 (Heap-based Buffer Overflow) and has a CVSS v3.1 base score of 5.5 (medium severity), with an attack vector of local access, low attack complexity, low privileges required, no user interaction, and impact limited to availability (no confidentiality or integrity impact). No known exploits are currently reported in the wild. Detection of exploitation attempts can be done by running the command 'request security policies check' and observing error logs indicating policy synchronization issues for PFE nodes. This vulnerability does not allow remote exploitation or privilege escalation but can disrupt network services by causing critical daemon crashes on affected devices.

For European organizations relying on Juniper SRX 5000 Series devices for network security and traffic management, this vulnerability poses a risk of service disruption due to Denial of Service attacks initiated by local authenticated users. Although the attack requires local access and low privileges, insider threats or compromised accounts could exploit this to disrupt critical network functions, potentially affecting business continuity and network availability. The impact is particularly significant for sectors with stringent uptime requirements such as finance, telecommunications, government, and critical infrastructure operators. The inability to maintain continuous network security services could lead to operational delays, increased incident response costs, and potential regulatory compliance issues under frameworks like NIS2 or GDPR if network outages affect data processing or security monitoring. However, the lack of confidentiality or integrity impact reduces the risk of data breaches or unauthorized data manipulation directly from this vulnerability.

European organizations should prioritize upgrading affected Junos OS versions to the latest patched releases as specified by Juniper Networks to remediate this vulnerability. Until patches are applied, organizations should implement strict access controls to limit local authenticated access to SRX 5000 Series devices, including enforcing strong authentication mechanisms and monitoring for unusual command execution patterns. Network segmentation and the use of jump hosts or bastion servers can reduce the risk of unauthorized local access. Additionally, continuous monitoring of device logs for the specific error message 'policies are out of sync for PFE node' can help detect exploitation attempts early. Incident response plans should include procedures for rapid NSD process restarts to minimize downtime. Regular security audits and vulnerability scanning of network devices should be conducted to ensure compliance with patch management policies. Finally, organizations should consider deploying intrusion detection or endpoint detection solutions capable of identifying anomalous local activity on network devices.