CVE-2025-21594 Information

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 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     256/2561         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.

CVSS Vector

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Reference

https://supportportal.juniper.net/JSA96449

Attack Complexity

LOW

Privileges Required

NONE

User Interaction Required

NONE

Scope

NONE

Confidentiality Impact

UNCHANGED

Integrity Impact

NONE

Availability Impact

NONE

Base Score

HIGH

Base Severity

7.5