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JunosOperating system · Juniper

CVE-2020-1670

MEDIUM · 6.5 CVSS v3.1 Published 2020-10-16
Mitigation only
No fix yet — a mitigation exists. There is no fixed release. A documented workaround reduces exposure in the meantime.
See remediation →
70/100
Remediation priority · Elevated
No privileges Zero-click

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
On Juniper Networks EX4300 Series, receipt of a stream of specific IPv4 packets can cause Routing Engine (RE) high CPU load, which could lead to network protocol operation issue and traffic interruption. This specific packets can originate only from within the broadcast domain where the device is connected. This issue occurs when the packets enter to the IRB interface. Only IPv4 packets can trigger this issue. IPv6 packets cannot trigger this issue. This issue affects Juniper Networks Junos OS on EX4300 series: 17.3 versions prior to 17.3R3-S9; 17.4 versions prior to 17.4R2-S11, 17.4R3-S2; 18.1 versions prior to 18.1R3-S10; 18.2 versions prior to 18.2R3-S4; 18.3 versions prior to 18.3R2-S4, 18.3R3-S2; 18.4 versions prior to 18.4R2-S4, 18.4R3-S2; 19.1 versions prior to 19.1R2-S2, 19.1R3-S1; 19.2 versions prior to 19.2R1-S5, 19.2R2-S1, 19.2R3; 19.3 versions prior to 19.3R2-S4, 19.3R3; 19.4 versions prior to 19.4R1-S3, 19.4R2; 20.1 versions prior to 20.1R1-S3, 20.1R2.

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis · high confidence

A denial of service vulnerability in Juniper EX4300 switches allows specially crafted IPv4 packets entering through an IRB interface to cause high CPU load on the Routing Engine, potentially disrupting network protocols and traffic. Only IPv4 packets from within the local broadcast domain can trigger this issue.

MitigationUpgrade Junos OS on EX4300 switches to a fixed version (17.3R3-S9, 17.4R2-S11, 18.1R3-S10, 18.2R3-S4, 18.3R2-S4, 18.4R2-S4, 19.1R2-S2, 19.2R3, 19.3R3, 19.4R2, 20.1R2, or later) within a scheduled maintenance window.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

NVD · CPE data
JunosOperating system
Affected:= 17.3= 17.4= 18.1= 18.2= 18.3= 18.4= 19.1= 19.2= 19.3= 19.4= 20.1

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Adjacent
Complexity
Low
Privileges
None
User interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
High

CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.

dbcve checks

Work through these to decide whether this CVE applies to you.

  1. Identify the device model
    Run 'show chassis hardware' or 'show system information' to confirm the device is an EX4300 switch
    Affected if Device is an EX4300 model
  2. Check the Junos OS version
    Run 'show version' and compare the firmware version to the affected list: 17.3, 17.4, 18.1, 18.2, 18.3, 18.4, 19.1, 19.2, 19.3, 19.4, 20.1
    Affected if Installed version matches any of the listed affected versions
  3. Verify IRB interface configuration
    Run 'show configuration interfaces irb' to check if any IRB interfaces are configured
    Affected if IRB interfaces exist in the configuration
  4. Confirm IPv4 is enabled on IRB
    Run 'show configuration interfaces irb | display set' and look for 'family inet' or 'unit X family inet' statements under IRB units
    Affected if IPv4 family (family inet) is configured on any IRB unit

A user is affected if they have an EX4300 running a Junos version from 17.3 to 20.1 with an IRB interface that has IPv4 configured, as packets entering that IRB can trigger the high CPU condition.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

From vendor data
Mitigation available No clean upgrade yet — mitigate in the meantime
Mitigation

Upgrade Junos OS on EX4300 switches to a fixed version (17.3R3-S9, 17.4R2-S11, 18.1R3-S10, 18.2R3-S4, 18.3R2-S4, 18.4R2-S4, 19.1R2-S2, 19.2R3, 19.3R3, 19.4R2, 20.1R2, or later) within a scheduled maintenance window.

Fix this in Junos Scoped from the published advisory
  • Consultation4.0 h
  • Implementation6.0 h
  • Testing6.0 h
  • Review / QA3.0 h
19.0 hours of engineering $3,320
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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2020-1670 in production — separate from our analysis above.

No notes yet

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What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
  • Verified mitigations, workarounds, and config changes
  • Version or environment caveats, and links to real fixes
  • No weaponised exploit code, or anything meant to cause harm
  • No spam, self-promotion, credentials, or personal data