CVE-2024-21610 is a vulnerability in Juniper Networks Junos OS affecting the Class of Service daemon (cosd). This flaw arises from improper handling of exceptional conditions (CWE-755) within cosd when processing specific low-privileged commands received over management protocols such as NETCONF, SSH, or telnet. The vulnerability manifests in scaled CoS deployments with thousands of interfaces, where the child management daemon (mgd) processes become stuck upon handling these commands. When mgd processes hang, SSH or telnet sessions also become stuck, eventually exhausting the connection limits for these protocols and preventing new management sessions from being established. This results in a limited Denial of Service (DoS) condition that impacts network management access but does not affect data plane traffic directly. The vulnerability affects multiple versions of Junos OS prior to various patch releases starting from 20.4R3-S9 up to 23.2R2, covering a broad range of currently deployed Juniper router and switch software versions. The attack requires an authenticated network-based attacker with low privileges, meaning the attacker must have some level of access to the management interfaces but does not need elevated privileges or user interaction. The CVSS 3.1 base score is 4.3 (medium severity), reflecting the limited impact on availability and lack of confidentiality or integrity compromise. No known exploits are reported in the wild as of the publication date. Detection of the issue can be done by monitoring mgd processes stuck in 'sbwait' state using Junos OS commands. This vulnerability primarily threatens the availability of management access to Juniper devices in large-scale CoS environments, potentially disrupting network operations and incident response capabilities.

For European organizations, the impact of CVE-2024-21610 centers on the availability and reliability of network management infrastructure. Juniper Networks equipment is widely used in enterprise, service provider, and government networks across Europe. Organizations operating large-scale networks with extensive Class of Service configurations and thousands of interfaces are particularly at risk. The inability to establish new SSH or telnet management sessions due to stuck mgd processes can delay or prevent administrators from performing critical network management, troubleshooting, and incident response tasks. This can lead to prolonged outages or degraded network performance if issues cannot be promptly resolved. While the vulnerability does not directly affect data plane traffic or compromise confidentiality or integrity, the loss of management access can indirectly increase operational risk and impact compliance with regulatory requirements for network availability and incident handling. The requirement for authenticated access limits exploitation to insiders or attackers who have already gained some foothold in the network, but the low privilege needed means that even limited access can be leveraged to cause disruption. European organizations with critical infrastructure, telecommunications providers, and large enterprises using Juniper Junos OS in scaled CoS deployments should consider this vulnerability a moderate operational risk.

1. Apply Juniper's official patches or upgrade to fixed Junos OS versions as soon as they become available, prioritizing devices running affected versions in scaled CoS environments. 2. Restrict and monitor access to management interfaces (NETCONF, SSH, telnet) to trusted administrators only, employing network segmentation and access control lists to limit exposure. 3. Implement strong authentication mechanisms, such as multi-factor authentication, to reduce the risk of unauthorized authenticated access. 4. Regularly monitor mgd processes for 'sbwait' states using the command 'show system processes extensive | match mgd | match sbwait' to detect early signs of exploitation or issues. 5. Limit the number of concurrent management sessions and configure session timeouts to reduce the impact of stuck sessions. 6. Employ network management redundancy and out-of-band management paths to maintain access if primary management sessions are disrupted. 7. Conduct periodic security audits and penetration testing focused on management plane security to identify potential weaknesses. 8. Educate network operations staff about this vulnerability and response procedures to quickly identify and remediate DoS conditions caused by stuck mgd processes.