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4.7Medium

Juniper Junos

CVE-2026-57031

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.

What this means for your business

  • It affects Juniper Junos. It matters if your company, or a supplier that handles your data, runs it.
  • An attacker can use it from inside the same network, without a login, and without anyone at your company clicking anything.
  • FIRST's prediction model gives it a 0.2% chance of attack attempts being seen in the next 30 days, ranking above 13% of all known flaws.

What to do

  1. 1Check whether your company or your suppliers run Juniper Junos, and which version. The affected versions are listed further down this page.
  2. 2If you do, apply the vendor's fix. A patch or vendor advisory has been published.

Not sure if your company is exposed?

Fastnexa’s certified penetration testers can check whether attackers could use this flaw, or others like it, against your websites, apps and network. The full test is free for our first 10 founding clients until 31 December 2026.

Check if you’re exposedBook a call

Scoring

CVSS
4.7 (v3.1)
Vector
CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:C/C:N/I:L/A:N
CVSS v4
5.3
Weakness
CWE-754
Assigned by
sirt@juniper.net

Dates

Published
2026-07-09
Last modified
2026-08-25
Sources
NVD

Affected products

  • Juniper Junos23.2, 23.4, 24.2, 24.4, 25.2
  • Juniper Lc4800all versions
  • Juniper Lc4802all versions
  • Juniper Lc9600all versions
  • Juniper Mpc10e-10call versions
  • Juniper Mpc10e-15call versions
  • Juniper Mpc11all versions
  • Juniper Mx304all versions

As listed in the NVD configuration data. Not a statement about your estate.

References