Instituto Nacional de ciberseguridad. Sección Incibe
Instituto Nacional de Ciberseguridad. Sección INCIBE-CERT

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CVE-2025-21594

Severity CVSS v4.0:
HIGH
Type:
Unavailable / Other
Publication date:
09/04/2025
Last modified:
26/01/2026

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).<br /> <br /> 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.<br /> Following is the command to identify the issue: <br /> <br /> <br />     user@host&gt; show services nat source port-block <br />     Host_IP                     External_IP                   Port_Block      Ports_Used/       Block_State/<br />                                                               Range           Ports_Total       Left_Time(s)<br />     2001::                        x.x.x.x                     58880-59391     256/256*1         Active/-       &gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt;port still usedThis issue affects Junos OS on MX Series: <br /> <br /> * from 21.2 before 21.2R3-S8, <br /> * from 21.4 before 21.4R3-S7, <br /> * from 22.1 before 22.1R3-S6, <br /> * from 22.2 before 22.2R3-S4, <br /> * from 22.3 before 22.3R3-S3, <br /> * from 22.4 before 22.4R3-S2, <br /> * from 23.2 before 23.2R2-S1, <br /> * from 23.4 before 23.4R1-S2, 23.4R2.<br /> <br /> <br /> This issue does not affect versions before 20.2R1.

Impact

Vector 4.0
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/R:U CVSS v4.0 Severity and Metrics:

Base Score: 8.70 HIGH
Vector: 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/R:U

Attack Vector (AV): Network
Attack Complexity (AC): Low
Attack Requirements (AT): None
Privileges Required (PR): None
User Interaction (UI): None
Confidentiality (VC): None
Integrity (VI): None
Availability (VA): High
Confidentiality (SC): None
Integrity (SI): None
Availability (SA): Low
Recovery (R): User

Base Score 4.0
8.70
Severity 4.0
HIGH
Vector 3.x
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H CVSS v3.1 Severity and Metrics:

Base Score: 7.50 HIGH
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Attack Vector (AV): Network
Attack Complexity (AC): Low
Privileges Required (PR): None
User Interaction (UI): None
Scope (S): Unchanged
Confidentiality (C): None
Integrity (I): None
Availability (A): High

Base Score 3.x
7.50
Severity 3.x
HIGH

Vulnerable products and versions

CPE From Up to
cpe:2.3:o:juniper:junos:21.2:-:*:*:*:*:*:*
cpe:2.3:o:juniper:junos:21.2:r1:*:*:*:*:*:*
cpe:2.3:o:juniper:junos:21.2:r1-s1:*:*:*:*:*:*
cpe:2.3:o:juniper:junos:21.2:r1-s2:*:*:*:*:*:*
cpe:2.3:o:juniper:junos:21.2:r2:*:*:*:*:*:*
cpe:2.3:o:juniper:junos:21.2:r2-s1:*:*:*:*:*:*
cpe:2.3:o:juniper:junos:21.2:r2-s2:*:*:*:*:*:*
cpe:2.3:o:juniper:junos:21.2:r3:*:*:*:*:*:*
cpe:2.3:o:juniper:junos:21.2:r3-s1:*:*:*:*:*:*
cpe:2.3:o:juniper:junos:21.2:r3-s2:*:*:*:*:*:*
cpe:2.3:o:juniper:junos:21.2:r3-s3:*:*:*:*:*:*
cpe:2.3:o:juniper:junos:21.2:r3-s4:*:*:*:*:*:*
cpe:2.3:o:juniper:junos:21.2:r3-s5:*:*:*:*:*:*
cpe:2.3:o:juniper:junos:21.2:r3-s6:*:*:*:*:*:*
cpe:2.3:o:juniper:junos:21.2:r3-s7:*:*:*:*:*:*

To consult the complete list of CPE names with products and versions, see this page


References to Advisories, Solutions, and Tools