CVE-2025-21594

published 2025-04-09

CVE-2025-21594: 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…

high 8.7 CVSS 4.0

AV N AC L AT N PR N UI N VC N VI N VA H SC N SI N SA L E X CR X IR X AR X MAV X MAC X MAT X MPR X MUI X MVC X MVI X MVA X MSC X MSI X MSA X S X AU X R U V X RE X U X

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 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.
Following is the command to identify the issue:

user@host> show services nat source port-block
Host_IP External_IP Port_Block Ports_Used/ Block_State/
Range Ports_Total Left_Time(s)
2001:: x.x.x.x 58880-59391 256/256*1 Active/- >>>>>>>>port still usedThis issue affects Junos OS on MX Series:

* from 21.2 before 21.2R3-S8,
* from 21.4 before 21.4R3-S7,
* from 22.1 before 22.1R3-S6,
* from 22.2 before 22.2R3-S4,
* from 22.3 before 22.3R3-S3,
* from 22.4 before 22.4R3-S2,
* from 23.2 before 23.2R2-S1,
* from 23.4 before 23.4R1-S2, 23.4R2.

This issue does not affect versions before 20.2R1.

Affected

18 ranges

Vendor	Product	Version range	Fixed in
juniper	junos	—	—
juniper	junos	—	—
juniper	junos	—	—
juniper	junos	—	—
juniper	junos	—	—
juniper	junos	—	—
juniper	junos	—	—
juniper	junos	—	—
juniper	junos_os	—	—
juniper	mx_series	—	—
juniper_networks	junos_os	< 21.2R3-S8	21.2R3-S8
juniper_networks	junos_os	>= 21.4 < 21.4R3-S7	21.4R3-S7
juniper_networks	junos_os	>= 22.1 < 22.1R3-S6	22.1R3-S6
juniper_networks	junos_os	>= 22.2 < 22.2R3-S4	22.2R3-S4
juniper_networks	junos_os	>= 22.3 < 22.3R3-S3	22.3R3-S3
juniper_networks	junos_os	>= 22.4 < 22.4R3-S2	22.4R3-S2
juniper_networks	junos_os	>= 23.2 < 23.2R2-S1	23.2R2-S1
juniper_networks	junos_os	>= 23.4 < 23.4R1-S2, 23.4R2	23.4R1-S2, 23.4R2

CWE-754