CVE-2025-21594

Name of the Vulnerable Software and Affected Versions: Junos OS versions 21.2 through 21.2R3-S8 Junos OS versions 21.4 through 21.4R3-S7 Junos OS versions 22.1 through 22.1R3-S6 Junos OS versions 22.2 through 22.2R3-S4 Junos OS versions 22.3 through 22.3R3-S3 Junos OS versions 22.4 through 22.4R3-S2 Junos OS versions 23.2 through 23.2R2-S1 Junos OS versions 23.4 through 23.4R1-S2, 23.4R2

Description: An Improper Check for Unusual or Exceptional Conditions vulnerability in the pfe (packet forwarding engine) of Juniper Networks Junos OS on MX Series causes a port within a pool to be blocked, leading to Denial of Service (DoS). In a DS-Lite (Dual-Stack Lite) and NAT (Network Address Translation) scenario, when crafted IPv6 traffic is received and the prefix-length is set to 56, the ports assigned to the user will not be freed. Eventually, users cannot establish new connections. Affected FPC/PIC need to be manually restarted to recover. The issue can be identified using the command show services nat source port-block.

Recommendations: For Junos OS versions 21.2 through 21.2R3-S8, update to version 21.2R3-S8 or later. For Junos OS versions 21.4 through 21.4R3-S7, update to version 21.4R3-S7 or later. For Junos OS versions 22.1 through 22.1R3-S6, update to version 22.1R3-S6 or later. For Junos OS versions 22.2 through 22.2R3-S4, update to version 22.2R3-S4 or later. For Junos OS versions 22.3 through 22.3R3-S3, update to version 22.3R3-S3 or later. For Junos OS versions 22.4 through 22.4R3-S2, update to version 22.4R3-S2 or later. For Junos OS versions 23.2 through 23.2R2-S1, update to version 23.2R2-S1 or later. For Junos OS versions 23.4 through 23.4R1-S2, 23.4R2, update to a version later than 23.4R2. As a temporary workaround, consider manually restarting the affected FPC/PIC to recover from the Denial of Service (DoS) condition.