CVE-2026-57031: An Improper Check for Unusual or Exceptional Conditions vulnerability in the packet forwarding engine (PFE) of

Routine

MEDIUM 4.7MITIGATE

CVE-2026-57031 is a medium-severity flaw (CVSS 4.7) affecting junos. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

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.

Why this priority

No elevated risk signals yet

No fix is published yet: follow the downgrade or mitigation steps.

Risk facts

CVSS score	4.7 (Medium)
Attack vector	Adjacent network
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	0.2% (top 87%)
CISA exploited list	No
Weakness	CWE-754
Published	2026-07-09
Last modified	2026-10-25

Publisher (CNA): Juniper Networks, Inc. · Vendor: juniper

Last updated 2026-10-25 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-07-09 22:17 UTCPublished CVE record published
2026-10-25 15:10 UTCUpdated Record last modified

juniper junos MITIGATE

Affected: 23.2 r2-s1 · 23.2 r2-s2 · 23.2 r2-s3 · 23.2 r2-s4 · 23.2 r2-s5 · 23.2 r2-s6 · 23.4 r2 · 23.4 r2-s1

Fixed in: no fixed release known

Safe to downgrade to: a release before 23.2

Check your OS release

cat /etc/os-release; uname -r

Debian / Ubuntu

sudo apt update && sudo apt full-upgrade

RHEL / Amazon Linux / Fedora

sudo dnf upgrade --refresh

Windows

Install the latest cumulative update from Windows Update

If no patch exists yet

OS downgrades are not safe. Apply the vendor mitigation from the advisory and restrict exposure.

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2026-57031?

junos: mitigate or apply the listed mitigation. Exact commands for each OS are on this page.

Is CVE-2026-57031 being exploited?

CVE-2026-57031 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2026-57031 affect?

CVE-2026-57031 affects junos. Severity is medium (CVSS 4.7). 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 w

How urgent is CVE-2026-57031?

Priority 20/100. No elevated risk signals yet.

Software pages

Juniper Junos vulnerabilities

Related CVEs

CVE-2026-57023 HIGH 7.5 MITIGATE An Improper Validation of Specified Quantity in Input vulnerability in the TCP proxy plugin of Juniper Network
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CVE-2026-57021 MEDIUM 5.3 MITIGATE An Out-of-bounds Write vulnerability in the http-gatekeeper (http-gk) of Juniper Networks Junos OS on SRX Seri
CVE-2026-57022 MEDIUM 5.9 UPGRADE An Improper Check for Unusual or Exceptional Conditions vulnerability in the Packet Forwarding Engine (PFE) of
CVE-2026-57030 MEDIUM 5.9 MITIGATE A Concurrent Execution using Shared Resource with Improper Synchronization ('Race Condition') vulnerability in

References

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