CVE-2025-21594

Junos OS: MX Series: In DS-lite and NAT scenario receipt of crafted IPv6 traffic causes port block

Severity Score

8.7

*CVSS v4

Exploit Likelihood

*EPSS

Affected Versions

*CPE

Public Exploits

*Multiple Sources

Exploited in Wild

*KEV

Decision

Attend

*SSVC

Descriptions

MITRE
TN

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.

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.

*Credits: N/A

CVSS Scores

Attack Vector

Network

Attack Complexity

Low

Attack Requirements

None

Privileges Required

None

User Interaction

None

System

Vulnerable | Subsequent

Confidentiality

None

Integrity

None

Availability

High

Low

Attack Vector

Network

Attack Complexity

Low

Privileges Required

None

User Interaction

None

Scope

Unchanged

Confidentiality

None

Integrity

None

Availability

High

Attack Vector

Network

Attack Complexity

Low

Authentication

None

Confidentiality

None

Integrity

None

Availability

Complete

* Common Vulnerability Scoring System

SSVC

Decision:Attend

Exploitation

None

Automatable

Yes

Tech. Impact

Partial

* Organization's Worst-case Scenario

Timeline

2024-12-26 CVE Reserved
2025-04-09 CVE Published
2025-04-10 CVE Updated
2025-04-15 EPSS Updated
---------- Exploited in Wild
---------- KEV Due Date
---------- First Exploit

CWE

CWE-754: Improper Check for Unusual or Exceptional Conditions

CAPEC

References (1)

URL	Tag	Source

URL	Date	SRC

URL	Date	SRC

URL	Date	SRC
https://supportportal.juniper.net/JSA96449	2025-04-10

Affected Vendors, Products, and Versions

Vendor		Product				Version		Other		Status
Vendor	Product	Version	Other	Status	<-- -->	Vendor	Product	Version	Other	Status
Juniper Networks Search vendor "Juniper Networks"		Junos OS Search vendor "Juniper Networks" for product "Junos OS"				< 21.2R3-S8 Search vendor "Juniper Networks" for product "Junos OS" and version " < 21.2R3-S8"		en		Affected
Juniper Networks Search vendor "Juniper Networks"		Junos OS Search vendor "Juniper Networks" for product "Junos OS"				>= 21.4 < 21.4R3-S7 Search vendor "Juniper Networks" for product "Junos OS" and version " >= 21.4 < 21.4R3-S7"		en		Affected
Juniper Networks Search vendor "Juniper Networks"		Junos OS Search vendor "Juniper Networks" for product "Junos OS"				>= 22.1 < 22.1R3-S6 Search vendor "Juniper Networks" for product "Junos OS" and version " >= 22.1 < 22.1R3-S6"		en		Affected
Juniper Networks Search vendor "Juniper Networks"		Junos OS Search vendor "Juniper Networks" for product "Junos OS"				>= 22.2 < 22.2R3-S4 Search vendor "Juniper Networks" for product "Junos OS" and version " >= 22.2 < 22.2R3-S4"		en		Affected
Juniper Networks Search vendor "Juniper Networks"		Junos OS Search vendor "Juniper Networks" for product "Junos OS"				>= 22.3 < 22.3R3-S3 Search vendor "Juniper Networks" for product "Junos OS" and version " >= 22.3 < 22.3R3-S3"		en		Affected
Juniper Networks Search vendor "Juniper Networks"		Junos OS Search vendor "Juniper Networks" for product "Junos OS"				>= 22.4 < 22.4R3-S2 Search vendor "Juniper Networks" for product "Junos OS" and version " >= 22.4 < 22.4R3-S2"		en		Affected
Juniper Networks Search vendor "Juniper Networks"		Junos OS Search vendor "Juniper Networks" for product "Junos OS"				>= 23.2 < 23.2R2-S1 Search vendor "Juniper Networks" for product "Junos OS" and version " >= 23.2 < 23.2R2-S1"		en		Affected
Juniper Networks Search vendor "Juniper Networks"		Junos OS Search vendor "Juniper Networks" for product "Junos OS"				>= 23.4 < 23.4R1-S2 Search vendor "Juniper Networks" for product "Junos OS" and version " >= 23.4 < 23.4R1-S2"		en		Affected
Juniper Networks Search vendor "Juniper Networks"		Junos OS Search vendor "Juniper Networks" for product "Junos OS"				>= 23.4 < 23.4R2 Search vendor "Juniper Networks" for product "Junos OS" and version " >= 23.4 < 23.4R2"		en		Affected