CVE-2025-21594

Summary

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 Software

Weaknesses

• CWE-754: CWE-754: Improper Check for Unusual or Exceptional Conditions

Workarounds

Modify the IPv6 prefix-length to be 64/96/128 through the command:

[ set services service-set <*> softwire-options dslite-ipv6-prefix-length 64/96/128]

ADP Enrichment

CISA ADP Vulnrichment

• SSVC:
• Exploitation: none
  • Automatable: yes
  • Technical Impact: partial

References

• https://supportportal.juniper.net/JSA96449

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