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JunosOperating system · Juniper

CVE-2020-1638

HIGH · 7.5 CVSS v3.1 Published 2020-04-08
Mitigation only
No fix yet — a mitigation exists. There is no fixed release. A documented workaround reduces exposure in the meantime.
See remediation →
84/100
Remediation priority · High
Remotely reachable 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
The FPC (Flexible PIC Concentrator) of Juniper Networks Junos OS and Junos OS Evolved may restart after processing a specific IPv4 packet. Only packets destined to the device itself, successfully reaching the RE through existing edge and control plane filtering, will be able to cause the FPC restart. When this issue occurs, all traffic via the FPC will be dropped. By continuously sending this specific IPv4 packet, an attacker can repeatedly crash the FPC, causing an extended Denial of Service (DoS) condition. This issue can only occur when processing a specific IPv4 packet. IPv6 packets cannot trigger this issue. This issue affects: Juniper Networks Junos OS on MX Series with MPC10E or MPC11E and PTX10001: 19.2 versions prior to 19.2R1-S4, 19.2R2; 19.3 versions prior to 19.3R2-S2, 19.3R3; 19.4 versions prior to 19.4R1-S1, 19.4R2. Juniper Networks Junos OS Evolved on on QFX5220, and PTX10003 series: 19.2-EVO versions; 19.3-EVO versions; 19.4-EVO versions prior to 19.4R2-EVO. This issue does not affect Junos OS versions prior to 19.2R1. This issue does not affect Junos OS Evolved versions prior to 19.2R1-EVO.

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 exists in the Flexible PIC Concentrator (FPC) of Juniper Networks Junos OS and Junos OS Evolved. When a specific IPv4 packet destined to the device itself reaches the Routing Engine (RE) through control plane filtering, it causes the FPC to restart, dropping all traffic through that FPC. Repeatedly sending this packet enables a sustained DoS attack. IPv6 packets cannot trigger this issue.

MitigationApply the vendor-supplied patches (upgrade to 19.2R1-S4/19.2R2, 19.3R2-S2/19.3R3, 19.4R1-S1/19.4R2, or 19.4R2-EVO as appropriate for the platform). As an interim control, ensure strict edge filtering blocks unknown or suspicious IPv4 traffic destined to the device before it reaches the control plane.

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:= 19.2= 19.3= 19.4
Junos Os EvolvedOperating system
Affected:= 19.2= 19.3= 19.4

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
Network
Complexity
Low
Privileges
None
User interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
High

CVSS:3.1/AV:N/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 Junos OS version
    Run 'show version' or 'request system version' command on the device
    Affected if The version is 19.2, 19.3, or 19.4 (any variant within these major.minor releases) on either Junos or Junos OS Evolved
  2. Verify FPC presence and status
    Run 'show chassis fpc' to list Flexible PIC Concentrators and their operational status
    Affected if Any FPC is online and processing traffic - the vulnerability causes FPC restart which drops traffic through that FPC
  3. Check for IPv4 control plane filters
    Run 'show configuration | match filter' and review input filters applied to loopback (lo0) or other interfaces accepting traffic destined to the device itself
    Affected if IPv4 input filters exist on the loopback interface or management interfaces that permit IPv4 packets to reach the Routing Engine
  4. Confirm IPv4 traffic handling to RE
    Review the device configuration for 'lo0' interface family inet address assignment and verify 'protocols' or 'firewall' filter configurations that process IPv4 traffic
    Affected if The device is configured to accept and process IPv4 packets destined to its own IP addresses (loopback or management IPs)

The device is affected if it runs Junos 19.2/19.3/19.4, has active FPCs, and accepts IPv4 traffic destined to the Routing Engine through control plane filtering.

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

Apply the vendor-supplied patches (upgrade to 19.2R1-S4/19.2R2, 19.3R2-S2/19.3R3, 19.4R1-S1/19.4R2, or 19.4R2-EVO as appropriate for the platform). As an interim control, ensure strict edge filtering blocks unknown or suspicious IPv4 traffic destined to the device before it reaches the control plane.

Fix this in Junos Scoped from the published advisory
  • Consultation2.0 h
  • Implementation4.0 h
  • Testing3.0 h
  • Review / QA1.0 h
10.0 hours of engineering $1,750
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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-2020-1638 in production — separate from our analysis above.

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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