Juniper Junos OS up to 23.4R1-S2 on MX Packet Forwarding Engine unusual condition

CVSS Meta Temp Score
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CTI Interest Score
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7.3$0-$5k0.00

Summaryinfo

A vulnerability has been found in Juniper Junos OS up to 23.4R1-S2 on MX and classified as critical. This affects an unknown function of the component Packet Forwarding Engine. This manipulation causes unusual condition. The identification of this vulnerability is CVE-2025-21594. It is possible to initiate the attack remotely. There is no exploit available. The affected component should be upgraded.

Detailsinfo

A vulnerability was found in Juniper Junos OS up to 23.4R1-S2 on MX. It has been declared as critical. Affected by this vulnerability is an unknown part of the component Packet Forwarding Engine. The manipulation with an unknown input leads to a unusual condition vulnerability. The CWE definition for the vulnerability is CWE-754. The product does not check or incorrectly checks for unusual or exceptional conditions that are not expected to occur frequently during day to day operation of the product. As an impact it is known to affect availability. The summary by CVE is:

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.

It is possible to read the advisory at supportportal.juniper.net. This vulnerability is known as CVE-2025-21594 since 12/26/2024. The exploitation appears to be easy. The attack can be launched remotely. The exploitation doesn't need any form of authentication. The technical details are unknown and an exploit is not publicly available. The pricing for an exploit might be around USD $0-$5k at the moment (estimation calculated on 01/26/2026).

The vulnerability scanner Nessus provides a plugin with the ID 237413 (Juniper Junos OS Vulnerability (JSA96449)), which helps to determine the existence of the flaw in a target environment.

Upgrading to version 20.2R1, 21.2R3-S8, 21.4R3-S7, 22.1R3-S6, 22.2R3-S4, 22.3R3-S3, 22.4R3-S2, 23.2R2-S1, 23.4R1-S2 or 23.4R2 eliminates this vulnerability.

The vulnerability is also documented in the vulnerability database at Tenable (237413). Be aware that VulDB is the high quality source for vulnerability data.

Productinfo

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CPE 2.3info

CPE 2.2info

CVSSv4info

VulDB Vector: 🔍
VulDB Reliability: 🔍

CNA CVSS-B Score: 🔍
CNA CVSS-BT Score: 🔍
CNA Vector: 🔍

CVSSv3info

VulDB Meta Base Score: 7.5
VulDB Meta Temp Score: 7.3

VulDB Base Score: 7.5
VulDB Temp Score: 7.2
VulDB Vector: 🔍
VulDB Reliability: 🔍

CNA Base Score: 7.5
CNA Vector (juniper): 🔍

CVSSv2info

AVACAuCIA
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VectorComplexityAuthenticationConfidentialityIntegrityAvailability
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VulDB Base Score: 🔍
VulDB Temp Score: 🔍
VulDB Reliability: 🔍

Exploitinginfo

Class: Unusual condition
CWE: CWE-754
CAPEC: 🔍
ATT&CK: 🔍

Physical: No
Local: No
Remote: Yes

Availability: 🔍
Status: Not defined

EPSS Score: 🔍
EPSS Percentile: 🔍

Price Prediction: 🔍
Current Price Estimation: 🔍

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Nessus ID: 237413
Nessus Name: Juniper Junos OS Vulnerability (JSA96449)

Threat Intelligenceinfo

Interest: 🔍
Active Actors: 🔍
Active APT Groups: 🔍

Countermeasuresinfo

Recommended: Upgrade
Status: 🔍

0-Day Time: 🔍

Upgrade: Junos OS 20.2R1/21.2R3-S8/21.4R3-S7/22.1R3-S6/22.2R3-S4/22.3R3-S3/22.4R3-S2/23.2R2-S1/23.4R1-S2/23.4R2

Timelineinfo

12/26/2024 🔍
04/09/2025 +103 days 🔍
04/09/2025 +0 days 🔍
01/26/2026 +292 days 🔍

Sourcesinfo

Vendor: juniper.net

Advisory: JSA96449
Status: Confirmed

CVE: CVE-2025-21594 (🔍)
GCVE (CVE): GCVE-0-2025-21594
GCVE (VulDB): GCVE-100-304279

Entryinfo

Created: 04/09/2025 22:28
Updated: 01/26/2026 22:31
Changes: 04/09/2025 22:28 (79), 05/28/2025 21:59 (2), 01/26/2026 22:31 (1)
Complete: 🔍
Cache ID: 216::103

Be aware that VulDB is the high quality source for vulnerability data.

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