---
id: CVE-2026-57031
title: >-
  An Improper Check for Unusual or Exceptional Conditions vulnerability in the
  packet forwarding engine (PFE) of Juniper Networks Junos OS on MX Series
  allows adjacent subscribers to bypass configured firewall filters.


  On MX Series device…
summary: >-
  An Improper Check for Unusual or Exceptional Conditions vulnerability in the
  packet forwarding engine (PFE) of Juniper Networks Junos OS on MX Series
  allows adjacent subscribers to bypass configured firewall filters.


  On MX Series device…
severity: medium
cvss: 4.7
cvssVector: 'CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:C/C:N/I:L/A:N'
cwe:
  - CWE-754
vendor: juniper
product: junos
affected:
  - junos = 23.2
  - junos = 23.4
  - junos = 24.2
  - junos = 24.4
  - junos = 25.2
published: '2026-07-09'
updated: '2026-08-25'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-57031'
references:
  - url: 'https://supportportal.juniper.net/JSA110091'
    label: sirt@juniper.net
tags:
  - nvd
epss: 0.00223
epssPercentile: 0.11588
ingestedAt: '2026-08-26T14:45:07.946Z'
---

## Overview

An Improper Check for Unusual or Exceptional Conditions vulnerability in the packet forwarding engine (PFE) of Juniper Networks Junos OS on MX Series allows adjacent subscribers to bypass configured firewall filters.

On MX Series devices with MPC10/11, LC4800/9600, and MX304 with subscribers configured on static interfaces, ingress firewall filters are not enforced, so that neither protocol level nor upstream bandwidth limitation are in effect. 


This issue affects Junos OS on MX with MPC10/11, LC4800/9600/4802, and MX304:


  *  23.2 versions from 23.2R2-S1 before 23.2R2-S7,
  *  23.4 versions from 23.4R2 before 23.4R2-S7,
  *  24.2 versions before 24.2R2-S3,
  *  24.4 versions before 24.4R2-S2,
  *  25.2 versions before 25.2R2.

## Affected

- `junos = 23.2`
- `junos = 23.4`
- `junos = 24.2`
- `junos = 24.4`
- `junos = 25.2`

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.