An Improper Handling of Exceptional Conditions vulnerability in the Class of Service daemon (cosd) of Juniper Networks Junos OS on MX Series allows an authenticated, network-based attacker with low privileges to cause a limited Denial of Service (DoS).
In a scaled subscriber scenario when specific low privileged commands, received over NETCONF, SSH or telnet, are handled by cosd on behalf of mgd, the respective child management daemon (mgd) processes will get stuck. In case of (Netconf over) SSH this leads to stuck SSH sessions, so that when the connection-limit for SSH is reached new sessions cant be established anymore. A similar behavior will be seen for telnet etc.
Stuck mgd processes can be monitored by executing the following command:
user@host> show system processes extensive | match mgd | match sbwait
This issue affects Juniper Networks Junos OS on MX Series: All versions earlier than 20.4R3-S9; 21.2 versions earlier than 21.2R3-S7; 21.3 versions earlier than 21.3R3-S5; 21.4 versions earlier than 21.4R3-S5; 22.1 versions earlier than 22.1R3-S4; 22.2 versions earlier than 22.2R3-S3; 22.3 versions earlier than 22.3R3-S2; 22.4 versions earlier than 22.4R3; 23.2 versions earlier than 23.2R1-S2, 23.2R2.
The product does not handle or incorrectly handles an exceptional condition.