PatchSiren

PatchSiren cyber security CVE debrief

CVE-2026-57031 Juniper Networks CVE debrief

CVE-2026-57031 is an Improper Check for Unusual or Exceptional Conditions vulnerability in the packet forwarding engine (PFE) of Juniper Networks Junos OS on MX Series. This allows adjacent subscribers to bypass configured firewall filters. The issue affects Junos OS on MX with MPC10/11, LC4800/9600/4802, and MX304 in various version ranges. Specifically, the vulnerability impacts devices with MPC10/11, LC4800/9600, and MX304 configurations where subscribers are configured on static interfaces, leading to a bypass of protocol level and upstream bandwidth limitations. Users of Juniper Networks Junos OS on MX Series should verify their systems against the affected versions and apply patches or mitigations as recommended by Juniper. The vulnerability details are based on information provided by Juniper Networks and recorded in the CVE and NVD databases.

Vendor
Juniper Networks
Product
Junos OS
CVSS
MEDIUM 5.3
CISA KEV
Not listed in stored evidence
Original CVE published
2026-07-09
Original CVE updated
2026-08-25
Advisory published
2026-07-09
Advisory updated
2026-08-25

Who should care

Users of Juniper Networks Junos OS on MX Series, particularly those with MPC10/11, LC4800/9600, and MX304 configurations, should verify their systems against the affected versions and apply patches or mitigations as recommended by Juniper.

Technical summary

The vulnerability CVE-2026-57031 exists in the packet forwarding engine (PFE) of Juniper Networks Junos OS on MX Series devices. It allows adjacent subscribers to bypass configured firewall filters when certain conditions are met, specifically on devices with MPC10/11, LC4800/9600, and MX304 with subscribers configured on static interfaces. This results in neither protocol level nor upstream bandwidth limitation being enforced. Affected versions include 23.2 from 23.2R2-S1 before 23.2R2-S7, 23.4 from 23.4R2 before 23.4R2-S7, 24.2 before 24.2R2-S3, 24.4 before 24.4R2-S2, and 25.2 before 25.2R2.

Defensive priority

Medium priority given the vulnerability's CVSS score of 5.3 and the potential for adjacent subscribers to bypass firewall filters.

Recommended defensive actions

  • Verify the Junos OS version on MX Series devices and compare it against the affected version ranges.
  • Apply patches or updates provided by Juniper Networks for the affected versions.
  • Review firewall filter configurations to ensure they are properly enforced.
  • Consider implementing compensating controls to monitor and restrict traffic if patching is not immediately feasible.
  • Perform a thorough review of network configurations to identify potential exposure.
  • Track and monitor network traffic for unusual patterns that could indicate exploitation.
  • Schedule regular security audits to ensure compliance with recommended mitigations.

Evidence notes

The CVE record was published on 2026-07-09T22:17:08.827Z and was last modified on 2026-07-10T15:16:45.443Z. The NVD entry is currently in the 'Received' status. The vulnerability details are based on information provided by Juniper Networks and recorded in the CVE and NVD databases.

Sources and references

Verified primary and authoritative sources

  • CVE-2026-57031 CVE Program record

    Publisher, destination, and source semantics verified

    URL: https://www.cve.org/CVERecord?id=CVE-2026-57031

    CVE Program - Official CVE Program record with source-provided CVE metadata.

  • CVE-2026-57031 NVD vulnerability detail

    Publisher, destination, and source semantics verified

    URL: https://nvd.nist.gov/vuln/detail/CVE-2026-57031

    NIST National Vulnerability Database - Official NIST NVD detail page and source-specific vulnerability assessment.

Supplemental references

Methodology and review provenance

AI-assisted synthesis based on stored public vulnerability evidence. System validation, approval state, and publication status do not by themselves establish human review of this revision. PatchSiren helps prioritize defensive review and does not prove exposure or remediation on any system.