On SRX Series devices, an Improper Check for Unusual or Exceptional Conditions when using Certificate Management Protocol Version 2 (CMPv2) auto re-enrollment, allows a network-based, unauthenticated attacker to cause a Denial of Service (DoS) by crashing the pkid process. The pkid process cannot handle an unexpected response from the Certificate Authority (CA) server, leading to crash. A restart is required to restore services. This issue affects: Juniper Networks Junos OS on SRX Series: All versions prior to 19.1R3-S9; 19.2 versions prior to 19.2R3-S6; 19.3 versions prior to 19.3R3-S7; 19.4 versions prior to 19.4R3-S9; 20.2 versions prior to 20.2R3-S5; 20.3 versions prior to 20.3R3-S4; 20.4 versions prior to 20.4R3-S4; 21.1 versions prior to 21.1R3-S1; 21.2 versions prior to 21.2R3; 21.3 versions prior to 21.3R2; 21.4 versions prior to 21.4R2.